conservation of cultural materials from

Archives and Museum Informatics 13: 291–323, 1999/2001.© 2001 Kluwer Academic Publishers. Printed in the Netherlands.

291

Conservation of Cultural Materials fromUnderwater Sites

DONNY L. HAMILTONNautical Archaeology Program, Texas A&M University, USA

Abstract. Underwater archaeology is the only branch of field archaeology that is dependent uponthe conservation laboratory for its ultimate success. In fact, in underwater archaeology the activitiesof the conservation laboratory are considered to be a continuation of the field excavations with therecording of basic data along with the stabilization, preservation, and study of the recovered materialbeing major objectives. Commonly used procedures for conserving ceramics, glass, bone, ivory,wood, leather, and the various metals are discussed. Observation and insights are presented on theapplicability of the different processes for conserving various materials.

Introduction

There has been a dramatic increase in all aspects of underwater archaeology overthe past decade. With this increased activity comes the responsibility to conservethe recovered materials – in other words to document, analyze, clean, and stabilizethem. In order to deal with the material properly, archaeologists and conservatorsshould know the history of the various conservation techniques frequently used.It is safe to say that relatively few procedures are utilized for the conservation ofwaterlogged cultural material and most are much the same as they were ten yearsago. Some of the newest conservation techniques require very specialized equip-ment that is out of the financial range of most laboratories; thus these techniquesplay a minor role in conservation. It is impossible to discuss in the limited spacehere all the procedures in use today for conserving waterlogged cultural material,but the core of conservation techniques and their inherent limitations need to beunderstood by all archaeologists. Readers interested in a more thorough introduc-tion to the subject are referred to Plenderleith and Werner (1977), UNESCO (1968),Hamilton (1976, 1996), Pearson (1987a), and Cronyn (1990).

Conservation of archaeological material is not just a set of procedures and treat-ments; it extends far beyond that. Often the conservator is the first and, in the caseof some very fragile items, may be the only person to see the actual artifact beforeit falls apart. The conservator’s responsibilities are those of archaeologist, mender,caretaker, and recorder of the artifacts that come into his or her care. Conservation,like archaeology is not just a set of techniques, it is a state of mind that holds adeep concern for the integrity of the artifacts, the context in which they are found,

292 DONNY L. HAMILTON

and what they represent as remnants of history. Archaeological conservation, there-fore, should always include documentation, analysis, cleaning, and stabilization ofan object. The objectives of cleaning and stabilization are to protect artifactual,faunal, and other archaeological materials and to prevent their reacting adverselywith the environment after recovery (Hamilton, 1976: 1). The term “preservation”usually refers only to cleaning and stabilization, but it is often used interchangeablywith conservation. In contrast, “restoration” refers to the repair of damaged objectsand the replacement of missing parts. A specimen may undergo both conserva-tion and restoration, but in many cases restorations are not attempted. Regardless,restoration should never be initiated without conservation.

Before discussing specific conservation procedures, it is important to point outan obvious fact concerning the excavation of an underwater or waterlogged site.Proper artifact preservation is one of the most important considerations during theplanning stage, before the site is excavated. Invariably, considerable material, muchof it organic, will be recovered and planning for artifact conservation must startearly.

Current Conservation Procedures

In the conservation of archaeological material, be it siliceous, organic, or metallic,from waterlogged sites, some authorities have found it convenient to separatethe conservation of material from freshwater sites from the conservation ofmaterial from marine sites. Yes, there are differences in deterioration and corrosionprocesses, but the fact remains that any laboratory set up to handle the conservationof material from marine sites is more than capable of handling every problem thatmight be encountered from any other type of site. A laboratory set up exclusivelyfor the conservation of freshwater material (Singley, 1988), however, cannot handlethe multitude of problems presented by the artifacts from the saltwater site. In theinterest of brevity, the conservation of the material from the two environments arediscussed together, but the emphasis is placed on the conservation of material frommarine sites. Where pertinent, specific differences and considerations are provided.In the majority of the cases, the two most overwhelming problems confronting theconservator responsible for conserving archaeological material from underwatersites are the conservation of iron and wood. This is especially true when dealingwith shipwreck sites. For this reason, the conservation of metals and organicremains are discussed first, followed by ceramics and glass. Much of what ispresented is based on first-hand experience and is concerned only with the timeframe and material associated with historic sites in the Americas.

Conservation of Metals Recovered from Marine Sites

The conservation of metal artifacts from a marine site, and to a lesser degree metalartifacts from a freshwater site, is not very similar to the conservation problems

CONSERVATION OF CULTURAL MATERIALS 293

presented by metal artifacts from most land sites. When artifacts are recoveredfrom the sea, especially warm areas such as the Caribbean and the Mediterranean,they are commonly encrusted with thick layers of calcium carbonate, magnesiumhydroxide, metal corrosion products, sand, clay, and various forms of marine lifesuch as shells, coral, barnacles, and plants. The term “encrustation” refers tothe conglomerations that may contain one or more artifacts. Such conglomera-tions may range from the size of a single coin to masses weighing severalthousand pounds containing hundreds of individual objects made of many differentmaterials. In the process of dealing with encrusted metal artifacts, which are inmost cases iron, one will encounter artifacts of other metals along with ceramics,glass, and various organic materials such as wood, leather, and bone. Thus, theconservation of encrustations with their concealed contents is analogous to anexcavation square within a site. Any laboratory that processes these encrustationshas the responsibility to preserve and stabilize the artifacts as well as conservationtechnology permits and to recover as much archaeological data as possible. Consid-erable information exists in the form of associations recoverable only by “in situ”observations made by the conservator. Extensive records have to be maintainedwhich include notes on the encrustation; the objects it contains; and the preser-vation techniques used; as well as color, black and white, and X-ray photographs.Casts have to be made of disintegrated objects and of significant impressions left inthe encrustations. One must detect such things such as potsherds, cloth fragments,spikes, straps, animal bones that are inevitably encased in the encrustation. Evenless obvious remains like impressions of seeds and insects, such as impressions ofcockroaches found in several encrustations from the 1554 Spanish Plate Fleet, mustbe detected and recorded. In other words, the conservator is in a unique position tosupply the archaeologist with valuable evidence and to provide the laboratory withbasic conservation data for research.

A typical example of an encrustation from a marine site exemplifies theproblem. In Figure 1 is just one of several large encrustations recovered from thesite of the “San Esteban”, one of the three ships of the 1554 Spanish Plate Fleetwrecked off Padre Island, Texas. This single piece contains two anchors, a wroughtiron, hooped barrel gun with its wooden undercarriage, three breech blocks, anda multitude of smaller objects. It is over four meters long and weighs over twotons. A laboratory must have sufficient space and equipment to take a piece likethis, mechanically clean it, properly recover and conserve the encased specimens,and possibly cast a number of natural molds of disintegrated objects. It may evenbe necessary to prepare the encased artifacts for display. The laboratory has tohave forklifts, chain hoists, large vats, specialized D.C. power supplies, hundredsof kilograms of chemicals, thousands of liters of deionized (DI) water among otherresources to perform the job. The laboratory must be prepared to take an encrusta-tion like that depicted in Figure 1, as well as hundreds of smaller encrustations andturn out an array of stabilized artifacts such as those depicted in Figure 2.


Figure 1. Large encrustation over 3 meters long and weighing over a ton containing twoanchors, a bombardetta gun, and over a hundred additional artifacts from one of the 1554Plate Fleet shipwrecks.

CONSERVATION OF IRON

The conserved wrought iron artifacts in Figure 2 are from the 1554 Fleet wrecks offthe coast of Padre Island, Texas. The wrecks from this fleet are the oldest verifiedships thus excavated in the Americas and serve as excellent examples for demon-strating techniques used to conserve some of the oldest iron artifacts recoveredfrom a marine site in the New World.

Iron recovered from a marine environment presents the conservator with hisbiggest problems. Iron, therefore, will be used to exemplify the basic require-ments of metal conservation in marine archaeology. Once iron has been recoveredfrom a marine environment, the corrosion process is accelerated, unless certainprecautions are taken, such as keeping artifacts wet after recovery. Quite oftenmany artifacts are not conserved until months or even years after recovery, so theymust be properly stored until treatment can begin. If iron is exposed to the air orplaced in an uninhibited aqueous solution, the ferrous compounds can oxidize toa ferric state occupying a greater volume and causing the surface of an artifact toscale off. Just this process alone can disfigure a piece and eventually destroy it.The greatest damage, however, is caused by various iron chlorides (both ferrousand ferric) found in iron recovered from marine environments. Hydrated ironchlorides, on exposure to moisture and oxygen, hydrolyze to form ferric oxide orferric hydroxide and hydrochloric acid. The hydrochloric acid in turn oxidizes theuncorroded metal to ferrous chloride and hydrogen, or ferric chloride and water.


Figure 2. Wrought iron artifacts from the 1554 Plate Fleet conserved by electrolytic reduction.One anchor, three hooped barrel gun tubes, and 12 breech blocks for the gun tubes.

This corrosion cycle continues until there is no metal remaining. For specifics ofiron corrosion, the interested reader is referred to Argo (1981), Gilberg and Seeley(1981), North (1982), and North and MacLeod (1987: 79–80). Because of thehigh chloride levels in the iron, electrolytic reduction is the only practical way ofconserving iron from marine sites; however, it is a safe practical way of conservingmetal artifacts from most archaeological environments.

Storage Prior to Treatment

Generally speaking, all metal objects should be kept submerged in tap water withan inhibitor added to prevent further corrosion. Alkaline inhibitive solutions suchas a 5% solution of sodium carbonate or 2% sodium hydroxide are most often used,but they must be checked regularly to keep the pH of the solution high (Hamilton,1976: 21–25). It is important that any adhering encrustation or corrosion layersshould be left intact until the objects are treated because they form a protectivecoating that retards corrosion. If iron artifacts are left encrusted, they can usuallybe stored in plain tap water for long periods. If the encrustation is removed, then analkaline solution is required to prevent the iron from corroding. If properly stored,the conservation can proceed in an orderly fashion with no need to rush the process.


Mechanical Cleaning

The mechanical cleaning process is one of the most important part of conservingthe large, encrusted iron artifacts. It is during this phase that most of the obser-vations on over-all associations are made. Where possible, X-rays are used todetermine the content of each encrustation and the condition of many of theencrusted objects. The X-rays also serve as a guide in extracting the artifacts fromthe encrustation and to determine the presence of molds. Some have proposedusing chemicals and even electrolytic reduction to remove the encrustation. Chem-icals are generally a very slow, ineffective process which can be damaging to anymetal artifact, and both chemicals and electrolytic reduction will destroy any moldsthat might be present. Well directed hammer blows on chisels are generally mosteffective in removing encrustations. However, for many objects, especially fragileobjects and ceramics, pneumatic tools are somewhat more efficient and precise.The small pneumatic air scribes manufactured by Chicago Pneumatic, which inessence are miniature, hand-held jack-hammers, are some of the most versatiletools for mechanically cleaning encrusted metal artifacts.

When mechanically cleaning encrusted iron artifacts, natural molds of formeriron artifacts are commonly encountered. The older the site, the more natural moldsof corroded iron artifacts will be found. If the objective is to recover the fullrange of artifacts at the site, these natural molds have to be cast in epoxy. Becauseencasing marine encrustation does not form on iron artifacts in fresh water, castingplays a minor role in their conservation.

Casting

The importance of casting the natural molds left by corroded iron artifacts cannot be over emphasized. It is a critical part of conservation that is often over-looked when dealing with encrusted iron artifacts from a marine site. Extensivecasting must be done, otherwise, a considerable amount of data on the full artifactassemblage will be lost. For instance, the majority of the small iron artifacts fromPort Royal, Jamaica which date from 1692, and the 1554 Plate Fleet ships offPadre Island have completely corroded. All that remains of them is a void withinthe encapsulating encrustation. These artifacts can still be recovered by breakinginto a strategic area of the encrustation, cleaning out the void, filling the void withepoxy, and then using a pneumatic air scribe to remove the marine encrustationsurrounding the epoxy cast. It is through casting the natural molds inside encrusta-tions that we were able to recover the complete array of small iron tools present atboth sites. In Figure 3 are two keys, a hammer, a cleaver, a door lock, and a socketedchisel, which are just a few of the hundreds of epoxy casts of iron tools from PortRoyal. Note that the handles on the hammer and the cleaver are the original woodwith the hammer head and the cleaver blade are epoxy casts. Wood will outlast ironin the sea, if it is covered with sediments to protect it against the various organismsthat will attack it.


Figure 3. Epoxy casts of iron tools from Port Royal, Jamaica. From top to bottom and leftto right: a hammer with the original wood handle, a cleaver with the original wood handle, adoor lock, two keys, and a socketed chisel.

In many instances some artifacts will have undergone a substantial amount ofcorrosion, but not enough to form a natural mold. In other instances part of theartifact is a mold, and other parts contain metal. In these cases, the voids arefilled with epoxy and after extracting the piece, a flexible mold has to be madeof the entire object so a good cast can be made of it. The sound iron artifacts thatare recovered have to undergo other conservation treatments, such as electrolyticreduction.

Electrolytic Reduction Cleaning of Iron

Iron, when it is recovered in a sound condition, can be conserved successfully. Ofthe techniques available for conserving iron from marine sites, none is as widelyused as electrolytic reduction but as widely misunderstood. The ease of set up andmaintenance, and the economy of an electrolytic unit, along with the versatility ofelectrolytic cleaning, make it one of the conservator’s most valuable tools. Unfor-tunately, too many conservators view electrolytic reduction as primarily a strippingprocess (Cronyn, 1990: 191) and are not aware of its full potential. Electrolyticreduction has been the most successful way of treating iron from a marine environ-ment. The process can be used for most metal objects, as long as they have asound metallic core. See Hamilton (1976: 30–49) for a detailed discussion ofthis technique. It can be selected exclusively for the mechanical cleaning actionproduced by the evolved hydrogen, for the reduction process or, as usually is thecase, a combination of the two. Efficient electrolytic reduction, however, involvesmore than wiring up artifacts for electrolysis. One must be familiar with electrodepotentials and pH, and how these variables relate to metal reduction, corrosion,passivation, and immunity (North, 1987: 223–227; Hamilton, 1976: 40–49). Thesefactors are particularly crucial when dealing with chloride-contaminated metals


from a marine environment. This is not to say that satisfactory results cannot beobtained by the novice, but rather that a good knowledge enables the conservatorbetter to understand and control processes in the electrolytic cell and to anticipateand correct adverse conditions.

Electrolytic reduction involves connecting an artifact to the negative terminalof a D.C. power supply, placing it in a vat containing an electrically conductivesolution called an electrolyte, such as 2–5% sodium hydroxide, and surroundingthe object with expanded steel mesh that is connected to the positive terminal of theD.C. power supply. In the reduction process some of the positively charged metalliciron ions in the corrosion compounds are reduced. In addition, the negativelycharged corrosive chloride ions and other anions are eliminated from the objectas they migrate toward the positively charged anode. Other procedural factors thatmust be considered are the equipment, such as type of power supply, terminal wiresand clips, anode material, vat, and the experimental variables such as the manner inwhich the electrolytic cell is set up, the electrolyte selected, chloride monitoring,electrode potentials, electrolyte pH, and current densities. In general, maximumreduction of the ferrous corrosion compounds is achieved if sodium hydroxide isused as the electrolyte and the current density kept low. As long as a low amperagerate is used during the initial stages, the corrosion layer and the original surface ofthe object can often be preserved. High current densities will strip off the corrosionlayers. For artifacts from a freshwater environment, electrolytic reduction has noparticular advantage other than convenience, and sodium carbonate is adequate forthe electrolyte.

Sodium Sulfite Treatment

The alkaline sulfite treatment was developed by North and Pearson (1975) tostabilize marine recovered cast iron, but it can be used on wrought iron. Generallyspeaking, the treatment is used to convert iron corrosion products to magnetite oniron artifacts that are too badly corroded for electrolytic reduction. Bryce (1979:21) found that the treatment is effective on iron objects that are moderately toheavily corroded, but they must have a metallic core; otherwise, the iron objectbreaks up.

Once the objects have been mechanically cleaned, they are immersed in a solu-tion of 0.5 M (20 g per liter of water) of sodium hydroxide and 0.5 M (126 g perliter of water) of sodium sulfite (North and Pearson, 1975: 5). Tap water can beused for the first one or two baths but deionized or distilled water should be usedin the final baths. The solution is mixed and the object placed in it as quickly aspossible to minimize contact of the solution with the air and the container shouldbe filled as full as possible to avoid any oxidation of the solution. The container,which for small objects may be a glass or polyethylene jar, is placed in an oven andkept heated to a temperature of 60 ◦C. The sulfite solution is changed several timesuntil the chlorides are removed from the metal. This may take a week or severalmonths. The solution does not attack any residual metal so there is no danger of too


many baths. When iron artifacts are immersed in this hot, reducing solution the ironcorrosion compounds are converted to magnetite and the chlorides are transferredto the solution, where they are discarded with each bath change. The iron objectscome out of the treatment with a very black surface coloration. Because the solutionis strongly alkaline, contact with the skin should be avoided.

While this treatment has been effective for conserving iron recovered from amarine environment, the main drawbacks of the process are that it has to be carriedout in an air-tight container, the solution must be kept heated, and it is difficultto determine when the chlorides have been removed from the iron and the treat-ment can be stopped. This treatment, like most conservation treatments, cannot behurried.

Hydrogen Reduction of Marine Iron

Hydrogen reduction of iron, both cast and wrought, recovered from a marineenvironment is sometimes used because of its potential of treating large artifactssuch as cannons and a large number of artifacts quickly. In hydrogen reductionthe objects are placed in a special furnace with hydrogen gas, or a mixture ofhydrogen and nitrogen, and heated to a temperature of 300 to 1,000 ◦C (Barkman,1977: 155–166). During the treatment, all the moisture is driven out of the arti-fact and the chloride corrosion compounds are volatilized. The hydrogen reducesthe iron corrosion compounds to a lower oxidation state and combines with theoxygen in the corrosion products, to form water, which is driven off by the heat.This treatment, while successful, has several drawbacks. First it requires ratherexpensive and sophisticated equipment that is outside the financial capabilities ofmost laboratoriesespecially for larger objects. The corrosive nature of the gasesproduced in the process have a detrimental effect on the equipment. Second, thereis the problem of the changes in the metallurgical characteristics of the metal whenheated to the temperatures necessary to drive off the chlorides if care is not taken(Tylecote and Black, 1980). This treatment is not enthusiastically endorsed as itwas for a period in the 1970s, but it is still commonly employed by some labora-tories to treat numerous artifacts such as cast iron shot. It is a treatment that can besuccessfully used, but caution should be exercised.

Treatment Following Stabilization

After iron objects have been treated by any of the techniques discussed above, it isimperative that their surfaces be covered with a protective coating to insulate themetal from the effects of moisture, chemically active vapors, and gases. For ironartifacts, the application of at least three coats of 20% tannic acid is recommendedbefore applying a final sealant. When tannic acid is applied to the surface of iron, achemical reaction converts the surface of the metal to ferric tannate, which is morecorrosion resistant than metallic iron (Farrer et al., 1953). It also gives the metal anaesthetically pleasing black color. Although some use the tannic acid coating as the


final step, I recommend that an additional sealant be applied over it for maximumprotection.

It is very important that any final sealant or coating provides a protective mois-ture barrier and prevents corrosion. In general, the sealant selected should be: 1)impervious to water vapor and gases, 2) natural-looking so that it does not detractfrom the appearance of the artifact, 3) reversible, and 4) transparent or translucentso any corrosion of the metal surface can be quickly detected. Immersion in moltenmicrocrystalline wax is one of the best sealants for both wrought and cast iron.Polyurethane coatings are also used (Hamilton, 1976: 55; North, 1987: 231) as wellas a clear drying zinc phosphate-based anti-corrosion primer followed by severalcoats of high durability, clear, matt polymethyl methacrylate acrylic lacquer (Northand Pearson, 1975: 177). With the exception of microcrystalline wax, all present aproblem if there is ever need to retreat the artifacts. The wax is easily removed byplacing it in a vat of boiling water.

The processes discussed here are adequate to handle the majority of iron arti-facts but there remains considerable room for improvements in the conservation ofiron.

CONSERVATION OF CUPROUS METALS

For this paper, the nonspecific term “cupreous metals” is used for copper and thealloys such as brass and bronze where copper predominates. In general it matterslittle what the specific copper alloy is, for it is usually treated in the same way.Special care needs to be taken when treating any copper alloy that contains a highpercentage of lead or tin, both of which are amphoteric metals and dissolve inalkalies. There are a number of chemical treatments for copper, bronze, and brass,but most are not satisfactory for cupreous metals from marine sites.

In a marine environment the two most commonly encountered copper corrosionproducts are cuprous chloride and cuprous sulfide. However, the mineral alterationsin the copper alloys are more complex than those of just copper. If a cupreousobject containing cuprous chlorides in its corrosion products is exposed to the air, itcorrodes by a process referred to as “bronze disease” where the cuprous chlorides,in the presence of moisture and oxygen, hydrolyze to form hydrochloric acid andbasic cupric chloride. The hydrochloric acid then attacks the uncorroded metalto form more cuprous chloride. The reaction continues until no metal remains.The conservation of chloride-contaminated cupreous objects requires that 1) thecuprous chlorides be removed, 2) the cuprous chlorides be converted to harm-less cuprous oxide, or 3) the chemical action of the chlorides be prevented. Thefollowing conservation treatments accomplishes one or more of these objectives.

Electrolytic Reduction Cleaning of Cupreous Metals

Electrolytic reduction of cupreous metals is an efficient method of removing thechlorides from cupreous artifact and is carried out in the same manner as described


for iron. The two alkaline electrolytes, 2% sodium hydroxide or 5% sodiumcarbonate, used on iron, as well as 5% formic acid can be used. If formic acidis chosen, stainless steel must be used for the anode; otherwise, mild steel is used.In contrast to iron, electrolytic cleaning of cupreous metals requires only a fewhours to a few days.

The main disadvantage of electrolytic reduction cleaning of copper alloys isthe tendency for copper to plate on the surface of the metal. This is especiallydistracting if either brass or bronze is being cleaned. It is sometimes difficult toremove the plated copper, but a short bath in 10% formic acid, and polishing withbaking soda is usually effective. Depending on the degree of chloride contami-nation, electrolytic reduction may not be required and satisfactory results can beobtained with alkaline rinses.

Alkaline Rinses

For cupreous artifacts with reasonably low chloride contamination, it is possible torinse the chlorides out in repeated alkaline baths and in the process cause littleor no alteration to any patina present. It is essential that the cuprous chloridepresent in the metal be removed to prevent any future outbreak of bronze disease.Cuprous chloride, however, is insoluble in plain water, a fact seemingly ignoredby some conservators (Patton, 1987: 43) and cannot be removed by washing inwater alone. Cuprous chloride is soluble in an alkaline solution where the hydroxylions of the alkaline solution react chemically with the cuprous chloride to formcuprous oxide and hydrochloric acid. The alkaline solution then neutralizes thehydrochloric acid. Successive changes of the alkaline solution continue until thechlorides are removed. The object is then rinsed in several baths of deionized wateruntil the pH of the last bath is unaltered.

Until recently, 5% sodium sesquicarbonate was used as the alkaline rinse solu-tion (Oddy and Hughes, 1970), but everyone who has used the treatment hasfound that it often results in an enhancement of the color of the patina and insome instances blackened the surface. Weisser (1987: 106) recommends using5% sodium carbonate instead. He found that it dissolved out less copper fromthe piece being treated and there was less alteration in the coloration of thepatina.

Benzotriazole

The use of benzotriazole (BTA) has become a standard part of any conserva-tion treatment of copper or copper alloy, following any stabilization process andpreceding any final sealant (Green, 1975; Sease, 1978). For artifacts from a fresh-water site, it may be the only treatment required; it being used to prevent any futurecorrosion or discoloration of the patina. For artifacts from a marine environmentother treatments, such as alkaline rinses or electrolytic reduction, usually have toprecede the application of BTA. The purpose of the BTA is to prevent the cuprous


chlorides left in the metal from reacting and to keep the cupreous metal fromtarnishing.

The best results are obtained when the cupreous artifact is immersed in 1–3%benzotriazole solution for 24 hours. The BTA is usually dissolved in water, butethanol can also be used. See Green (1975), Hamilton (1976), and Sease (1978) foradditional information. The benzotriazole forms an insoluble, complex compoundwith cupric ions. Precipitation of this insoluble complex over the cuprous chlorideforms a barrier against any moisture that could activate the cuprous chloridesresponsible for bronze disease. The treatment does not remove the cuprous chloridefrom the artifact, it merely forms a barrier between the cuprous chloride and themoisture in the atmosphere. For artifacts heavily contaminated with chloride, thetreatment may have to be combined with one of the other treatments describedabove. Use of this method alone is not always successful; however, it should be partof any treatment of copper or copper bearing alloys. Because BTA is a suspectedcarcinogen, contact with the skin should be avoided and the powder should not beinhaled.

Final Treatment and Sealant

Following electrolytic or chemical cleaning, the objects are put through a series ofhot rinses in deionized water. Because copper tarnishes in water, Pearson (1974:302) recommends washing in several baths of denatured ethanol. If a water rinse isused any tarnish that develops can be removed with 5% formic acid or by polishingwith a wet paste of sodium bicarbonate (baking soda). After rinsing, cupreousobjects should be treated with BTA as described above. After drying in acetone, theartifact is coated with a protective coating of clear acrylic. Many conservators useIncralac, which is an acryloid resin with BTA incorporated into it. Alternatively,benzotriazole can be mixed with Acryloid B-72 or polyvinyl acetate and brushed onthe artifact. I have found that Krylon Clear Acrylic Spray #1301, which is AcryloidB-66 resin dissolved in toluene, is satisfactory. Krylon is recommended for ease ofapplication, durability, and availability. Microcrystalline wax can be used, but inmost cases has no special advantage over acrylics.

CONSERVATION OF LEAD AND LEAD ALLOYS

Once recovered from the sea, the corrosion products of objects of lead or leadalloys such as pewter, are stable. They may be unsightly or even disfiguring, butthey do not take part in chemical reactions that attack the remaining metal, as isthe case with iron, copper, and copper alloys. The artifacts need to be cleanedonly for aesthetic reasons and to reveal surface details under the corrosion layers.A number of techniques are used (Lane, 1979). Old pewter, being an alloy of leadand tin needs to be treated as tin, which is the more anodic and chemically sensitivemetal. Therefore, no acids or sodium hydroxide should be used on it. Most of the


pewter plates recovered from the excavations at Port Royal, Jamaica, as well asmost of the lead pieces, were conserved by electrolytic reduction.

Electrolytic Reduction Cleaning of Lead

This treatment is carried out in the same way as described for iron; however,considerable care must be taken when alkaline electrolytes are used as lead willdissolve in them unless the D.C. electrical current is flowing to the artifact. Thepower must never be turned off when lead or pewter objects are in electrolysis.For this reason, an electrolyte of sodium carbonate is often used, for if the currentstops, a layer of lead carbonate is formed on the lead, preventing further attack.However, more metal reduction is possible with sodium hydroxide. After treatinglead and pewter objects with alkaline electrolytes, the conservator should rinsethem in several baths of dilute sulfuric acid (four drops of 15% sulfuric acid perliter of water) until the pH ceases rising (Plenderleith and Werner, 1977: 269–270).Any residual acidity from the sulfuric acid rinses is then removed by immersion insuccessive baths of cold deionized water until the pH remains constant with that ofthe water.

Chemical Treatment of Lead

Because of the ease of treatment and the availability of the chemicals, the mostwidely used treatment for lead from any archaeological environment is the acidtreatment described by Caley (1955). The lead is immersed in 10% hydro-chloric acid, which removes lead carbonates, lead monoxide, lead sulfide, calciumcarbonate, and ferric oxide. If lead dioxide is present, it is removed by soakingthe object in 10% ammonium acetate. Care should be taken with the ammoniumacetate for it can etch the metal. For most lead objects, the ammonium acetate stepis not required. This treatment is good for lightly corroded specimens and it giveslead surfaces a pleasing appearance. The surface detail that is preserved by thistreatment varies with the degree of corrosion when recovered. In practice, Caley’smethod has been superseded by electrolytic reduction, when there is a concern toconvert lead corrosion back to a metallic state. However, for the general cleaningof lead, without a lot of hands-on labor, it remains a much used and acceptabletechnique provided that all residue from the HCl is removed.

Sealant

Following the conservation treatment and rinsing, lead and pewter objects shouldbe dried with hot air or dehydrated in a water miscible solvent such as acetone.Then they should be sealed by immersion in hot microcrystalline wax or sprayedwith an acrylic spray as described for copper.


Storage of Lead Objects

Lead is particularly susceptible to organic acids, such as acetic, humic, and tannicacid. Lead artifacts, therefore, should not be stored in oak cabinets or drawers.Because the vapor from wood can initiate corrosion, lead should be stored in sealedcontainers or polyethylene bags.

CONSERVATION OF SILVER

After iron, silver suffers the most damage from a saltwater environment. Thickencrustations form around the metal and objects undergo considerable attack bysulfate reducing bacteria. Accordingly, the most commonly encountered corrosionproducts on silver and silver alloys in a marine environment are silver sulfide andsilver chloride. Both compounds are stable mineral forms and do not take part inany further corrosive action with the remaining silver. Therefore, like lead, silvercorrosion products need to be removed only for aesthetic reasons and to revealdetail hidden by the corrosion layers. Base silver alloys with copper, however,differ because copper corrodes preferentially and forms cuprous chloride, whichcontinues to corrode the copper component of the silver. In these cases the silveris treated as if it were copper. For marine recovered silver, there are a number oftreatments available (MacLeod, 1987; MacLeod and North, 1979) but the mainalternatives are 1) electrolytic reduction and 2) alkaline dithionite, both of whichconvert the silver corrosion products back to metallic silver.

Electrolytic Reduction

The electrolytic cleaning of silver takes advantage of the reduction action of elec-trolysis by removing chloride and sulfide ions from silver chloride and silversulfide, and by reducing the silver in the corrosion compounds to a metallic state.Possible electrolytes include 5% sodium carbonate, 2% sodium hydroxide, and 5%formic acid; however, maximum metal reduction is achieved with an electrolyteof sodium hydroxide. During the process, the current density must be very low toachieve maximum reduction (Charlambous and Oddy, 1975). This can be accom-plished in most instances by regulating the D.C. power supply so that three volts areestablished in the cell (Pearson, 1974: 299). When using a formic acid electrolyte,only inert anodes such as stainless steel No. 316 or platinized titanium should beemployed. Mild steel is recommended over stainless steel when sodium hydroxideis used. Both electrolytes have their application depending upon the nature of thesilver corrosion products.

Alkaline Dithionite

The alkaline dithionite treatment (MacLeod and North, 1979) is similar to that ofalkaline sulfite described for iron. It is a relatively cheap, simple and rapid method


of consistently reducing silver corrosion products to metallic silver. In this treat-ment, if the silver objects are covered with marine encrustation, they are immersedin 10–12% hydrochloric acid to remove any encrustation layer consisting of sand,shell, calcium carbonate, copper, and, in some cases, iron corrosion compounds.The acid treatment, which may last from a day to a week, continues until allevolution of gas ceases.

After the hydrochloric acid treatment, the silver is rinsed thoroughly in tap waterto remove all residual encrustation. If necessary, any stubborn spots are removedmechanically. The silver is then sealed in a solution of alkaline dithionite that isprepared by first mixing 40 g of sodium hydroxide per liter of water. Once thesodium hydroxide dissolves, 50 g of sodium hydrosulfite are added to the solutionand the silver is then immersed quickly to eliminate the possibility of the solutionoxidizing from exposure to atmospheric oxygen. The container for the solutionshould be completely full to eliminate any air space and capable of being sealed sothat it is air tight.

During the treatment, the container is agitated on a regular basis to keep thesolution mixed and to expose all surfaces of the specimens to the solution. Afterapproximately one week, the silver artifacts are removed and rinsed in deionizedor distilled water until the pH of the rinse water remains unchanged.

The alkaline dithionite treatment will effectively reduce the silver corrosionproducts to a gray, metallic silver which can be polished with a wet baking sodapaste or a fiberglass brush to a silvery luster.

This alkaline dithionite treatment has been a very effective way of convertingbadly mineralized silver back to metallic silver. The technique has been used toconserve a large number of silver coins from several Dutch East India Companyships (MacLeod and North, 1979) and I have used it to separate and consolidate astack of five silver plates from a 1691 Spanish wreck that were encrusted together.In addition to being a recommended treatment for reducing silver, it is also beenvery effective for converting badly mineralized copper buttons and brass rings backto a metallic state.

Rinse and Sealant

Following electrolysis or any chemical cleaning, the specimens should bethoroughly rinsed in deionized water. If an alkaline electrolyte or chemical wasused, the rinsing should be more intensive. The silver is dried with hot air ordehydrated in acetone and coated with clear acrylic lacquer such as Krylon ClearAcrylic 1301.

GOLD AND GOLD ALLOYS

Gold is a very noble and inert metal that does not corrode; therefore, gold andhigh gold alloys do not require any treatment. The copper and/or silver corrosion


compound of low alloy gold are treated by the same techniques described for thosetwo metals.

Conservation of Wood

Being of organic origin, wood normally decays under combined biological andchemical attack when buried in the ground and submerged in water. It can, however,survive for prolonged periods when in either a very dry or a waterlogged environ-ment. When wood is deposited in an underwater site, it undergoes a complicateddeterioration process (Grattan, 1982, 1987), but we can generalize certain factsfrom the published data. First, however, for conservation purposes, it is veryimportant to know whether the wood is hardwood or softwood, and in manyinstances even the species because each species possesses unique characteristics.Hardwoods, such as oak, are broadleaf Angiosperms that have vessel pores. Soft-woods, or Gymnosperms, such as pine, are needle bearing trees or conifers thatlack vessel pores. After long periods in wet soil, peat bogs and marine sites,bacterial action causes a degradation of the cellulosic components of cell walls ofall wood. In general, water soluble substances such as starch and sugar disappearfrom wood first, along with mineral salts, coloring agents, tanning matters andother bonding materials. In time, through hydrolysis, cellulose in the cell wallsdisintegrates, leaving a lignin network to support the wood. As the cellulose andlignin disintegrate, the wood becomes more porous and permeable to water andthe cell cavities and intermolecular spaces fill with water. The remaining ligninstructure of the wood cells and the absorbed water preserve the shape of the wood.As long as the waterlogged wood objects are kept wet they will retain their shape. Ifthe wood is exposed to the air, the excess water evaporates and the surface tensionof the evaporating water will cause the weakened cell walls to collapse, causingconsiderable shrinkage and distortion.

Live trees contain a lot of water. After the tree is cut, the wood looses moistureuntil it reaches an equilibrium with its local environment. In the process of airdrying, the wood shrinks and the dimensions of the wood used to make artifactsis reflective of the cured, dried wood. Waterlogged wood swells from its manu-factured size. Once recovered and treated, the treated wood will shrink to varyingdegrees depending upon how it was treated. Some shrinkage is acceptable and, infact desired, for the waterlogged wood has swelled, but the degree of shrinkagemust be within acceptable bounds. Proper conservation will control the amount ofshrinkage. In practice, a particular conservation technique is often selected becauseit is known that the wood treated by it will shrink a desired amount (Patton, 1987:43).

Waterlogged wood is commonly conserved by a process that involves eitherremoving the excess water by replacing it with a material that consolidates andconfers mechanical strength to the wood or the excess water is removed by amethod that will prevent any shrinkage or distortion of the wood. The most


commonly used of the many treatments for the conservation of waterlogged woodare polyethylene glycol, acetone/rosin, and sugar, which are examples of the firstalternative above. Various forms of dehydration and freeze drying are examples ofthe second alternative.

If the wood is recovered from a freshwater environment, it usually contains anegligible amount of soluble salts. If the wood is from a marine environment, thewater bulking the cells is full of soluble salts. Prior to any of the conservationtreatments described below, it is necessary to take the wood through a numberof freshwater baths to remove the bulk of the salts. Otherwise, a precipitate ofcrystallized white salt can form on the surface of the treated piece. Except for theneed to remove most of the soluble salts that might be present, there is no differencebetween the conservation of wood recovered from a marine environment or a fresh-water environment. Another consideration in the treatment of marine wood is thepresence of teredo worms and their calcareous tunnels. Teredo worm infestationcan be so extensive that the wood has a mushy, spongy consistency. In fact, thecalcareous burrows of the teredo may be all that is holding the wood together.There is a wide range of conservation treatments for wood (Grattan and McCawley,1987). Depending upon the circumstances, the choice of treatment may be basedon nothing more than aesthetics. Different treatments result in different colors ofwood, provide differing susceptibility to fluctuation of humidity, different storagerequirements, different shrinkage rates, differing degrees of flexibility, the abilityto glue composite pieces together, and the affect the treatment chemicals haveon any composite wood/metal artifact. The treatment accorded is based on theseconsiderations, thus every conservator has to have a range of treatments available.

POLYETHYLENE GLYCOL (PEG) METHOD

The PEG method was the first method for treating waterlogged wood that wassimple to carry out and economically efficient. It continues to be used widely.Although the PEGs have some of the physical properties of waxes, they are distin-guished from true waxes by the fact that they are freely soluble in water and alcohol(ethanol, methanol, isopropanol). Polyethylene glycols are synthetic materialswhich have the generalized formula HOCH2·(CH2OCH2)n·CH2OH (Pearson,1979: 51). The low molecular weights (300–600) are liquids, the intermediatemembers are semi-liquids or have the consistency of Vaseline (1,000–1,500) andthe higher molecular weights (3,250–6,000) are wax-like materials. The lowerthe molecular weight, the smaller the size of the molecules, the more easily itpenetrates and the more hygroscopic it is. The higher molecular weight PEGshave large molecules, do not penetrate as well, and are less hygroscopic. PEGsof different molecular weight have different applications, depending on the speciesand condition of the wood undergoing the treatment.

During the PEG treatment, the excess water in the wood is removed and thewood is bulked in one operation. There are any number of variations in the treat-


ment, most of which involve heating the solution. Smaller objects can be placedin a ventilated, heated oven where the temperature is gradually increased until,over a period of time it reaches 52–60 ◦C (125–140 ◦F). Larger vats have to usecirculation pumps and various means of heating the solution. Small increments ofPEG are added to the heated solution to increase its concentration. The size of theincrements depends on the species of wood and its condition. The increments canbe as low as a fraction of a percent, but in general tend to be in the range of 1–2%.When using PEG in water it is necessary to use a fungicide to prevent mold growth.

Because water is obviously much cheaper than any of the various alcohols(ethanol, methanol, isopropanol) it is generally used as the solvent when largepieces of wood are treated with PEG. In most instances smaller pieces of woodcan be treated in an alcohol/PEG solution. When alcohol is used as the solvent, thewaterlogged wood is generally dehydrated and then increments of PEG are addedat the rate determined for that piece. In general, alcohol/PEG treated wood is lighterin color, lighter in weight, and the treatment takes less time, and there is no needfor a fungicide.

PEG treated wood tends to be relatively heavy, especially when water andlower molecular weight PEG is used. It can be flexed, but it is difficult to gluetreated pieces together. In general, the treatment is not recommended for compositewood/metal artifacts, for PEG is corrosive to most metal, especially iron. In addi-tion, any metal component can be adversely affected by long emersion in heatedwater, especially when PEG is present. Although some conservators have usedPEG on composite pieces, it is not recommended. See the acetone/rosin treatmentbelow.

SUCROSE METHOD

Ever since waterlogged wood has been recovered and treated, there has been asearch for a less expensive, but dependable way to treat it. PEG provided oneoption, but even less expensive methods were needed. Back in the early 1970s,I was experimenting with sucrose treatments and one of my students, JamesParrent (1985), investigated the process in greater detail. The treatment procedureis exactly the same as described for PEG, except that sugar is used. The advantagesof using sugar are that its molecules are about the same size as the lower molecularweight PEG, they readily penetrate the wood; the treatment time is reduced, andthe sugar is much less hygroscopic than PEG of any molecular weight.

Before starting the conservation, all the adhering dirt should be removed, andthe bulk of any soluble salts should be removed. The wood is then placed in a 1–5% solution of sugar dissolved in water. Only refined white sugar (pure sucrose)should be used. The brownish colored, coarse grained unrefined sugar (Type Asugar) should be avoided, for wood treated in it is much more hygroscopic thanwood treated in refined, white sugar. With highly degraded wood it is possibleto start with a higher concentration of sucrose; however, if in doubt, start with a


1% weight/volume solution. Once the wood is saturated with a given x% sugarsolution the concentration is increased by 1% to 10% depending upon the condi-tion of the wood and the species of tree being treated. Usually, once the woodhas reached equilibrium at a 50% solution, increments of 10% can be made. Formost specimens, a 70% sugar concentration is all that is required for successfultreatment.

When the wood has reached equilibrium with the desired percentage of sugar,it is removed and allowed to undergo slow, controlled drying as it adjusts to theprevailing atmospheric conditions, as is the case in all the wood treatment describedhere. This will maximize the success of the overall treatment. The wood should bestored under conditions of less than 70% humidity.

In general, the results are comparable to that of the various PEG treatments, butat less expense. The advantages of the treatment are that the wood is dimensionablystable with less shrinkage than comparable PEG treated wood. It is less expensivethan PEG, it is soluble in water, and the small molecular size of the sugar shortensthe treatment time. The disadvantages are a heavy wood that does not flex, it hasa duller, matte surface, and there is a tendency for some surface checking. Thetreatment is not recommended for composite wood/metal artifacts since the metalmay corrode while submerged in a heated sugar/water solution. Finally, there isthe potential problem presented by having an edible artifact. Still, the problems ofinsects and rodents eating the sucrose treated wood can be eliminated with properstorage conditions.

Sugar or sucrose treatments remain a viable alternative for treating as econom-ically as possible large pieces of waterlogged wood, such as canoes and structuralparts of ships. Maintaining artifacts treated by sugar in a controlled atmosphere willensure the continued success of the conservation procedure. Artifacts thus treatedrequire no more or no less care than those treated with other preservatives. Thismethod constitutes an acceptable means of conserving waterlogged wood and isthe least expensive of the methods discussed here. Sugar was used successfully totreat a number of door frames and sills from Port Royal, Jamaica.

ACETONE/ROSIN METHOD

The acetone/rosin treatment was developed to overcome the difficulty that thehigher molecular weight PEGs had in penetrating the dense heartwood of well-preserved oak (McKerrell and Varsanyi, 1972). The treatment consists of replacingthe water in wood with pine rosin, also called colophony. The procedure for treatingwaterlogged wood with acetone/rosin (McKerrel and Varsanyi, 1972) is a simpleprocess. The treatment starts with removing any dirt that may be present and if thepiece was recovered from a marine site, the soluble salts should be rinsed out. Insome cases a pretreatment in dilute muriatic acid, which is the name for technicalgrade hydrochloric acid (HCL) may be warranted. The acid treatment is said toimprove the penetration of the rosin into the wood by breaking down the organic


acids in the wood and bleach the wood to a more natural or original color. However,based on my experience, I do not recommend pretreating the wood in hydrochloricacid. Caution is warranted, for wood treated with HCl shrinks more, the surfaceoften becomes checked and it is more prone to cracking after the conservationtreatment is completed. In general, HCl pretreatment can be detrimental to thewood, and its other supposed purpose of lightening the color of the wood does notoccur. I have found that the bleaching is only temporary and rarely affects the finalcolor of the treated piece. For marine recovered wood that has any degree of teredoworm infestation, the HCL will dissolve the calcareous tunnels and considerablyweaken the wood. This step should be considered optional and is not generallyrecommended.

If the acid pretreatment is not used, then the first step following the generalcleaning is dehydrating the wood completely in 3 successive baths of acetone, eachbath lasting 2–4 days depending on the thickness of the wood. This step of thetreatment is very important, for all the water must be removed before placing itin the saturated rosin solution. If any water is present in the wood, it will create abarrier for the rosin which is not soluble in water.

In the actual treatment process, the wood is placed in a sealed containercontaining a saturated solution of rosin dissolved in acetone. A saturated solu-tion of 67% rosin can be achieved in acetone at 52 ◦C. To insure that a saturatedsolution is present, an excess of rosin should be placed in the container so thatthere is a thick viscous layer along the bottom of the container. The object beingtreated should be suspended or supported above this thick undissolved rosin. Thewood should be placed into the rosin solution when it is at room temperature. Thewood and the rosin solution are then heated together to 52 ◦C by placing them in athermostatically controlled, explosion-proof oven. Raising the temperature of thebath after placing the wood in it creates less of a shock to the wood than if it wereplaced directly into a heated solution. Treatment time may last from two weeks toseveral months. McKerrel and Varsanyi (1972) suggest that objects 5–10 cm thickcould be treated in 4 weeks, while objects less than 5 cm thick require 2 weeks.After the wood is saturated with rosin, each piece is removed from the containerand the excess rosin is wiped off with a rag moistened with acetone. Because of thecost and danger of using the organic solvent, this treatment is usually used only onsmall, important objects, but with a little thought and ingenuity, larger objects canbe safely treated.

Of the conservation treatments available today, this one has a high successrate. It results in a warm-colored wood that is totally dry. Because the wood isimpregnated with rosin, it is less susceptible to changes in the relative humidity,and is, therefore, more independent of its storage environment. For this reason,the acetone/rosin treatment is preferred when good storage conditions can not beassured for conserved waterlogged wood. Other advantages of the acetone/rosintreatment are that it is light in weight, it is dry, it can be glued and repaired easilyif it breaks, it is strong, and it can be used on compound wood and metal objects,


such as rifles, for the rosin does not react with any of the associated metals. Thus, itis considered by many to be the treatment of choice for all composite wood/metalartifacts. Its disadvantages include the high cost of the organic solvents and therosin, and the flammability of the acetone. In cases where it is necessary to recon-struct a composite piece, and where it may be necessary to flex a piece of wood,acetone/rosin would not be an ideal choice because the treated wood will break ifit is bent. I have had much better success when the treatment was increased two tothree times longer than recommended. It should also be noted here that, while betterand quicker results are achieved with a heated solution, I have treated a numberof odd-shaped wood objects in an acetone/rosin solution at room temperature. Atroom temperature the rosin solution is less than 67%, but the treatments have beensuccessful.

Over the past 10 years, I have always preferred the various rosin treatmentswhen I wanted to be assured of success. Colophony rosin is soluble in ethanol andisopropanol. The saturated solution in these two solvents is less than 67% but bothhave been successfully used, in both heated and unheated treatments, to treat water-logged wood. Both are less volatile and flammable than acetone, and can be usedin polyvinyl chloride (PVC) containers. For example, a waterlogged Tower 1862Enfield rifle from North Carolina and a War of 1812 rifle from Lake Champlain,both composites of wood, iron and brass, were successfully treated in ethanol/rosinat room temperature in a PVC pipe. When room temperature treatments are used,regardless of the solvent, the treatment time should be increased considerably (6–12 months) to ensure the artifact is completely saturated with the rosin solution.The use of alternative alcohol solvents makes the rosin treatment more versatile,and the over-all success is similar. It is important that water-free alcohol or acetonebe used to ensure success.

DEHYDRATION

Treatment of waterlogged wood by dehydrating it through a series of alcohol bathsand freeze-drying are often employed, but is it important to remember is thatdehydration treatments can only be used on wood that has enough mechanicalstrength to support itself after conservation. This treatment is not applicable forbadly degraded wood. The main factor that keeps conservators from relying onboth much more is the cost of the solvents and the freeze drying equipment. Inmost cases, only relatively small objects can be treated in the freeze-drying unitscommonly found in conservation laboratories.

The early attempts at freeze-drying waterlogged wood were not too successful,for the surface of the treated wood was prone to surface checking. This problemwas solved by Ambrose (1975) when he pretreated the wood with PEG 400. Now,the standard freeze-drying treatment consists of cleaning the wood thoroughly andthen saturating it in 10–20% PEG 400. Ambrose (1975) recommended using 10%PEG 400, while Watson (1987: 274) states that a 20% concentration is preferable,


for this more concentrated solution prevents the formation of bacterial slime thatforms in the soaking bath. Conservators have developed a number of variations onthe freeze-drying treatment (Watson, 1987) which employ various combinationsand concentrations of PEG 400 and PEG 3350 (4000) pretreatments, dependingupon the condition of the wood. A PEG 3350 pretreatment will bulk the wood andmake freeze-drying treatment possible for wood that could not otherwise supportitself after treatment.

After being saturated with the PEG solution, the wood is frozen solidly in alow temperature freezer. The PEG in the wood prevents the formation of large icecrystals, which can disrupt the wood cells during the freezing stage. The frozenwood is then placed in the freeze-drying chamber and a low vacuum is maintainedduring the treatment. Under vacuum, the ice crystals sublime and the ice goesdirectly from a solid state to a gaseous state without an intervening liquid state,causing minimal shrinkage. The gas or water vapor that forms freezes and collectson the low temperature condenser in the freeze-drying unit. After a period of daysto weeks, depending on the size of the wood and the capacity of the freeze-dryingunit, all the water is removed from the wood and the PEG is left in the wood asa humicant and stabilizer. Freeze drying is often used to conserve small pieces ofwaterlogged wood. However, because it is a dehydration process, it often resultsin excessive shrinkage, especially if the wood is badly degraded. The techniqueremains an option for select pieces.

The treatments for waterlogged wood described above are the ones mostcommonly used on a daily basis by many conservation laboratories. There areothers that have not been as successful. Still, new, reliable techniques need to bedeveloped. We need new substances that are not hygroscopic that will penetratethe wood readily and will set up in the wood to prevent the cells from shrinking.Research is continuing on a number of substances that look promising.

Leather Conservation

To be frank, there are no totally acceptable ways to treat waterlogged leather. Thecomplaints made by Jensen (1983) nearly a decade ago are still applicable today. Agood review of conserving waterlogged leather is presented in Jensen (1987) andsome of the more general applicable procedures are presented here.

All archaeological leather conservation is preceded by washing to remove anyingrained dirt. First try washing in water alone. If this is not successful, try alter-native methods. Leather may require a variety of mechanical cleaning techniques,depending on the condition of the leather and the particular cleaning problem. Softbrushes, water jets, and ultrasonic cleaners may be required. If chemical cleaning isnecessary to remove ingrained dirt, a small amount of non-ionic detergent (about a1% solution) or sodium hexametaphosphate can be used. Rinse well after washing.Do not use any chemicals that will damage the collagen fibers of the leather anddo not use any heated solutions. When conserving leather it often safer to select


a treatment that least affects the leather. For waterlogged leather, freeze dryingand solvent dehydration, as described for wood above, are often selected, withoutadding any additional lubricant.

One must always remember that it is often better to leave stains on the leatherin order to prevent damage that may occur while attempting to remove them. Forstain removal, particularly iron staining, 3–5% ammonium citrate and disodiumethylenediamine tretraacetate (EDTA) are used. Soak the leather in one of thesesolutions for 2–3 hours or until the stains are removed, monitor the process closely;then rinse the leather in running water or standing tap water until all chemicalresidues are removed. Check the pH of a standing bath of water containing theleather to determine complete removal of the chemicals. Always keep in mindthat chemicals used to clean rusts and mineral concretions may produce furtherhydrolysis of the proteinaceous collagen fibers, leather’s main constituent, and thatthey can remove tanning, coloring agents, painted decorations and other featuresthat are part of the diagnostic attributes of the leather object. Diagnostic attributesshould never be removed. Caution should be exercised when using any of thesechemicals on leather.

Dehydration Using Organic Solvents

This treatment is identical to the process of dehydrating wood by taking it througha series of baths of water miscible organic solvent. In most cases a sequence ofsolvents with decreasing polarity is used, e.g., a series of baths of x% H2O–x%isopropanol, a bath of 100% isopropanol, a bath of 100% ethanol or methanolfollowed by 100% methyl ethyl ketone, then 100% acetone and finally 100% ether.Slow desiccation of glutinous collagen fibers allows their surfaces to become lesssticky and less brittle, thus more flexible. This example is a very conservativemethod of treatment. In most instances fewer baths are used and for some leather,drying only through acetone is necessary. All residue of the drying solvents isremoved by air drying, sometimes using a vacuum. If necessary, a lubricant suchas PEG 400 can be added.

PEG Treatments for Waterlogged Leather

When treating leather with PEG 400, 540 Blend, 600, 1450, and 3350, it is recom-mended that you start with a dilute solution (1–10%) of PEG and gradually increasethe concentration through evaporation of the solvent or by adding PEG up to 30%–80%. This allows the water to evaporate as equal amounts of PEG replace the water.Heated solutions should not be used and PEG concentrations in excess of 30% arenot necessary.

Aqueous solutions of PEG are slower, but less expensive. Solvent solutions aremuch faster, considerably more costly, but produce a lighter leather with moreuniform shrinkage. Some conservators prefer alcohol treatments, while others think


that alcohol treatments cause the leather to shrink more than comparable aqueoustreatments. Both techniques are applicable in given situations.

Bone, Ivory

Both bone and ivory are composed of inorganic calcium phosphate associatedwith carbonate and fluoride and an organic tissue called ossein (Plenderleith andWerner, 1977: 149). In waterlogged archaeological sites, the ossein is decomposedby hydrolysis and is reduced to a sponge-like consistency. The surface of eithercan spall off and there is a tendency for it to split along the grain. Ivory willdelaminate around its circular rings. Quite often, archaeological bone and ivorycan only be cleaned, strengthened and stabilized; satisfactory restoration is oftenimpossible. The conservation of waterlogged bone from underwater sites involvesremoving insoluble and soluble salts, removing stains, and consolidating the bonewith synthetic resins.

REMOVAL OF SOLUBLE SALT

In many ways the problems of soluble salts and stain removal in bone conservationare similar to pottery. Bone, ivory, teeth, antler, are all porous, thus they will adsorbsoluble salts and stain easily. Treatment of structurally sound bone starts with theremoval of any surface dirt and then the removal of any soluble salts. The salts areremoved by going through rinses of tap water, rain water, and deionized water, asdiscussed under ceramics. Structurally unsound bone artifacts require much morecareful hands-on cleaning, and the specific process is dictated by the condition ofeach individual artifact. In some instances the bone is so delicate that it must beconsolidated before the rinsing is initiated. The removal of insoluble salts such ascalcium carbonate and various stains from bone/ivory can be a tricky process. Ingeneral the insoluble salts should be removed mechanically if possible. If this is notpossible, considerable thought should be given as to whether they should actuallybe removed.

Bone and ivory artifacts, because of the anisotropic nature of the material, arenot normally allowed to air dry. This is especially true for thin artifacts such as bonelice combs. Drying is best accomplished by taking the object through graded bathsof alcohol. After drying through acetone, the bone/ivory should be consolidated byimmersion in a dilute solution (5–10%) of PVA resin (V7 or V15) or in AcryloidB-72 resin dissolved in acetone.

STAIN REMOVAL

Stains present other problems, for in too many cases, bone/ivory artifacts aredamaged in the process of removing stains. In all cases, one should consider leavingthe stain on the object. In some instances, when the decision has been made to


remove iron stains, 5–10% oxalic acid, disodium EDTA, 5% ammonium citrate byitself and 5% ammonium citrate followed by 5% oxalic acid have been successfullyused. For sulfide stains, 5–10% hydrogen peroxide is used.

Unsound bone presents a multitude of problems. In most cases it is treatedwith localized applications of the acid with a brush or swab. If unsound boneis submerged in an acid solution, the evolution of carbon dioxide from thedecomposition of the CaCO3 will break up the specimen.

After cleaning any bone/ivory artifact with any chemical, all traces of that chem-ical must be removed by rinsing. The treatment then follows the same procedure aswhen rinsing soluble salts out of the artifact. Most bone is then treated by applyinga synthetic resin such as PVA or Acryloid B-72 in order to provide it with additionalmechanical strength and to seal it of from the moisture of the atmosphere.

Ceramics

Generally speaking, the conservation of ceramics recovered from archaeologicalsites is very straightforward and only minimal treatment is required (Olive andPearson, 1975; Mibach, 1975; Pearson, 1987b, 1987c). One of the main thingsthat needs to be determined first when one conserves ceramics is whether they areearthenware, stoneware, or porcelain. The latter two are fired at higher tempera-tures and are relatively impervious to liquids. Earthenware, which constitutes thebulk of the ceramics from any period, is fired at much lower temperatures and willadsorb liquids along with any soluble substances that may be in the solution; thus,earthenware pieces require more treatment.

All ceramics should be washed to remove all the adhering dirt. Well-firedpottery can be washed in a mild detergent, scrubbing the edges and surfaces witha soft brush. Care should be taken not to mar the surfaces or to remove traces offood, paint, pigments, and soot that is left on either surface. Fragile, badly firedpottery requires more care, but the procedure is the same. Fragile pieces, potterywith friable surfaces or flaking surfaces may require consolidation with a syntheticresin before treatment.

REMOVAL OF INSOLUBLE SALTS

Quite often at marine sites, archaeologists recover ceramics that have becomeencapsulated by the calcareous encrustation that forms around iron artifacts andthey can be partially covered by the various corals that can grow on the surfaceof ceramics exposed on the ocean’s bottom. In most cases the safest and mostsatisfactory method of removing insoluble salts from the surface of pottery ismechanically by hand. Most calcareous concretions can be removed easily whenwet by scraping with a scalpel, dental tool, or pneumatic chisels.

In limited instances, insoluble salts can be removed chemically, but one needsto be very judicious when chemicals are used. Hydrochloric acid, oxalic acid, and


ethylenediamine tetraacetate are commonly employed. Before using any acid onpottery make sure that the paste does not contain carbonate temper (shell, calciumcarbonate) for the tempering material will be removed, thoroughly weakening thebody of the ceramic. Simple precautions such as thoroughly wetting the sherd withwater before applying the acid will concentrate the action on the surface. Wellconsolidated sherds can be immersed in the acid until all gas evolution ceases –usually less than an hour – and repeated if necessary. Care must be exercised, forhydrochloric acid can discolor glazes, especially lead glazes, which will turn milky.After using any acid the sherds should be rinsed first in tap water, followed byrinses in either rain water or de-ionized water. They are then allowed to air dry.

Ethylene-diaminetetraacetic acid or ethylene-diaminetetraacetate (5–10%EDTA, tetra-sodium salts) is used to remove calcareous and iron deposits fromthe surface of ceramics without seriously affecting the iron content of the paste(Olive and Pearson, 1975: 64). In this treatment the sherds are immersed in thesolution and left until the deposits are removed. Periodically, the solution may haveto be replenished. In the process, the iron stains that are usually bound in with thecalcium salts are removed along with the calcium.

REMOVAL OF SOLUBLE SALTS

When pottery is recovered from freshwater sites there are seldom sufficient solublesalts (chlorides, phosphates, nitrates) in the body of the sherd to present a problemand no treatment other than rinsing off dirt and possibly consolidation of theearthenware is required. Pottery excavated from brackish and marine sites issaturated with soluble salts and in some cases the surfaces become covered withinsoluble salts such as calcium carbonate. The soluble salts must be removed forthe pottery to be stable because soluble salts are hygroscopic and they repeatedlydissolve and crystallize as the relative humidity rises and falls. The salts eventuallyreach the surface of the pot, crystallize and expand, exfoliating off the surfaceand crazing the glazes. The process can continue until it actually breaks up thepiece through internal stresses and fractures. In other cases, masses of needle-likecrystals can cover the surface of the sherds or pot, hiding all detail.

Generally speaking, soluble salts will not penetrate the body of porcelain andstoneware; but, in some cases, salts can be deposited below the glaze of either,where they can crack and in some cases lift off the surface glaze. Both porcelainand stoneware seldom require much conservation, but whenever in doubt, or whenthere is a possibility of salts penetrating the glaze, they should be treated in thesame way as the earthenware.

Soluble salts are easily removed by repeated rinsing in water; a running bathis quicker and more effective but is very wasteful. The old conservation trick ofplacing sherds in the reservoir of a toilet is a very effective way of rinsing out saltswith continuous changes of water and free labor. Once the level of the salts arebrought to the level of the local tap water, then deionized water may be used for a


final bath or two. When pottery is being rinsed in separate baths, the progress canbe monitored with a conductivity meter to determine when to change the baths andwhen the treatment is completed. Alternatively, silver nitrate can be used to test forthe presence of sodium chloride in a sample of the rinse water.

STAIN REMOVAL

Iron oxide stains are one of the more common stains encountered. If the decisionis made to remove them, local application of 10% oxalic acid with cotton swabson the surface of wet pottery is generally successful in removing iron stains fromstoneware and earthenware ceramics which contain iron oxide in the paste or glaze.In other cases the ceramics are submerged in the EDTA solution until the ironstains are removed. Five percent EDTA, disodium salt is recommended for use onpottery containing iron oxide in the glaze or paste because it dissolves less iron outinto solution. In all treatments, caution must be exercised to avoid overcleaning.Intensive rinsing after cleaning is required. Stains should be left unless there is anoverriding reason to remove them.

In marine sites, and even many wet land sites, black sulfide staining of ceramicglazes is very common. In fact, nearly all of the tin enamel ceramics such as delftand majolica excavated from the submerged town of Port Royal, Jamaica werebadly stained with sulfides. This type of staining is easily removed by immersing in10–25% by volume hydrogen peroxide solution for a short period of time – minutesto hours – until the stains disappear (Olive and Pearson, 1975: 65). The processshould be carefully monitored, especially on tin enamel wares (delft, majolica,faience), because the glaze on these ceramics is often crazed and the hydrogenperoxide solution can flow under it and the bubbles generated during treatment canlift off the poorly attached glaze. If the glaze is friable, and loose, the hydrogenperoxide should be applied with a cotton swab and observed closely. By blot-ting and reapplying the hydrogen peroxide, the stains can be removed. Hydrogenperoxide is also useful for removing organic stains. One note of caution: concen-trated hydrogen peroxide is potentially one of the most dangerous chemicals usedin conservation. Wear gloves at all times and use caution if concentrated solutionsare used to make the dilute working solutions, for it will burn skin very badly.

RECONSTRUCTION

When it is necessary to glue sherds together, a good reversible glue, such asAcryloid B-72 or PVA, should be used (Koob, 1986). In the past celluloid gluessuch as Duco have been used, but they have too short a serviceable life to be usedin conservation (Selwitz, 1988). A thick PVA solution in acetone, acetone/tolueneor acetone and amyl acetate can be used. Very friable and fragile sherds may haveto be consolidated in a dilute solution of the glue before they are glued or repaired.


Glass Conservation

Glass is usually the most stable of archaeological materials, but it can go throughsome complex disintegration processes (Brill, 1962; Moncrieff, 1975). In my ownexperience, I have found glass to be either no problem at all, or a complete disaster.Unfortunately there are few in between cases. Whether or not there are problemsdepends more upon the original composition of the glass than upon anything else.Ideally, glass should consist of 70–73% silica, 16–22% alkali or soda ash (sodiumcarbonate) or potash (potassium carbonate, usually derived from wood ash) and 5–10% flux, usually lime (calcium oxide). The alkali lowers the melting point of thesand and the flux facilitates the mixture of the components. As long as the mixtureis kept in balance, glass is stable. Problems arise when there is an excess of alkaliand too little flux in the glass mixture, for then it will be especially susceptibleto attack by moisture. In water, especially saltwater, the sodium and potassiumcarbonates can leach out leaving only a fragile, porous hydrated silica (SiO2)network. This causes the glass to craze, crack, flake and pit giving the surface ofthe glass a frosty appearance. In some cases there is an actual separation of layersof glass from the body.

There are considerable differences of opinion on what to do with unstable glass.Some advise that the only treatment should be to keep the glass in low relativehumidities so the glass does not react with any excess atmospheric moisture. Whilea RH range of 40% to 55% is usually recommended, it varies in relationship to thestability of the glass. The weeping or sweaty condition is sometimes made worse bythe application of a surface lacquer or sealant, for resin sealants are not imperviousto water vapor, and the disintegration continues under the sealant until the glassfalls apart. Other glass conservators try to remove the alkalinity from the glass tohalt the deterioration.

GLASS TREATMENT

From my underwater excavations of Port Royal, Jamaica I have found that themajority of the glass that we excavated has been stable and required little attention.Conservation problems are most often encountered with the early lead crystal,simple sulfide staining of leaded glass, and the cheap liquor bottles of the late17th and early 18th centuries, commonly called “Onion” bottles.

Historically, it took a while to formulate a stable lead glass. The early formu-lations were unstable and were very subject to crazing. When examples of earlylead glass were encountered in the Port Royal excavations, they were badly frac-tured. Conservation consists of rinsing the pieces thoroughly with de-ionized waterand then controlled drying through graded alcohol baths, followed by consoli-dation under vacuum, with dilute PVA or Acryloid B-72. Then hours are spentreconstructing the angular, fractured pieces.

The other problem often encountered with lead glass is its tendency to developa black lead sulfide film over its entire surface, in the same way as described for


the various tin enamel ceramics. In marine sites, lead stem ware and various cut,lead crystal pieces are solid black when recovered. A 10–15% hydrogen peroxidesolution, as described for ceramics, is used to remove the sulfide stain. Fragmentscan then be glued together with a good glue or when deemed necessary, a clearepoxy formulated for glass.

The ubiquitous liquor bottles of the 17th century are made of a very cheaplymade green soda glass that is unstable in sea water. During the deteriorationprocess, it develops a layer of dead, opaque glass that forms layers like an onionskin. In many cases the deterioration goes completely through the glass and thebottle literally falls apart in a matter of minutes upon exposure to air. In othercases, there is a residual layer of sound glass under the deteriorated glass and thepieces can be preserved by keeping then stored in freshwater until conservationcan be started. If required, mechanically clean the bottle of adhering encrustation.Do as much mechanical cleaning as possible without damaging the bottle. Thenplace the bottle in a bath of 2% sulfuric acid to remove any remaining calcareousdeposits and to neutralize the alkalinity of the glass. The bottle is then thoroughlyrinsed in de-ionized water. The bottles are then dried in several baths of ethanolor acetone and either a PVA or an Acryloid B-72 resin is applied under a vacuumto secure the layers of glass in place. The bottle should then be stored in relativehumidity of 40% or below to ward off any future breakdown of the glass.

GLASS RECONSTRUCTION

Glass can be repaired and reconstructed with the same glues as described forpottery, but clear epoxy resins are generally used because they adhere to thesmooth, non-porous glass more readily. They dry clearer and shrink less than thesolvent resins and are, therefore, less noticeable and develop stronger bonds. Theepoxy resins are, however, usually irreversible. It is exceptionally difficult and timeconsuming to fill the gaps left by missing pieces and it is also difficult to matchtransparent glass colors. Glass reconstruction should be left to a glass specialist.

Conclusion

This chapter has attempted to present the current state of conservation of archae-ological material from waterlogged environments as evidenced by the proceduresin common use. Various requirements and procedures have been discussed, butmany more were not. Time and space did not allow a thorough discussion ofeach technique; therefore, individuals interested in archaeological conservationshould consult the referenced sources and a trained conservator before attemptingthe procedures described herein. The preservation of antiquities should produceobjects that are chemically stable with an aesthetically acceptable appearance. Alltreatments should be reversible in the event that the object should require additionalpreservation.


Successfully conserved objects may still deteriorate in the future. Only if storedor displayed under optimum conditions can stability be assured. Metal artifacts, aswell as those made of organic or siliceous material can become chemically unstablefrom myriad causes and require periodic inspection and evaluation, as well aspossible retreatment. At our present stage of knowledge, perhaps it is most realisticto say that the objective of archaeological conservation is to delay reprocessing aslong as possible by proper storage and to make any necessary retreatment simpleand brief. Conserving the recovered artifacts is just one of the responsibilities.

Much more is contributed by the conservation laboratory than simply an arrayof stabilized artifacts. The conservation laboratory documents the associations,photographs the artifacts, makes preliminary identifications, conducts preliminaryresearch on the items, arranges or conducts various analytical tests, has woodsamples, bones, and other faunal material identified, and makes casts of artifacts,in addition to cleaning and stabilizing the material.

Clearly, detailed information can be lost if an attempt is made to process archae-ological material in inadequate facilities or in the field because many of the artifactsare completely converted to corrosion products or deteriorated. Although thesespecimens are not recoverable, their provenances can be recorded and measure-ments taken in situ can be shown in scaled drawings. Their presence is just asimportant as the artifacts that survive intact. Additional information is recoveredby casting the natural molds and impressions found of disintegrated objects. Occa-sionally, the only possible documentation is in the form of in situ photographsand measurements from which reconstructions can be made. At time, recordedobservations have to suffice.

The costs of conservation force some hard decisions. With the continuingincreases in the cost of utilities, equipment, chemicals, and labor, it is not econom-ically feasible to treat every artifact from a site. Large objects pose special problemsbecause of the equipment required to process them and the great expense inevit-ably involved. The decision as to what to treat or not to treat must be worked outwith the investigating archaeologist. Factors such as budget, facilities, and timeare important considerations. In lieu of total conservation, photographs, and scaleddrawings will have to suffice for the more common specimens and even for someof the less ordinary pieces.

As one learns the various conservation techniques, reads the textbook descrip-tions, and processes artifacts, it becomes necessary to improvise continually.Occasionally the most appropriate equipment or facilities are not available andit is up to the conservator to manipulate what is at hand to fulfill the necessaryrequirements. In the process, the skills of a conservator, as normally defined, mustalso include the qualities of an administrator, an electrician, a chemist, and even acarpenter, a mechanic, a welder, and particularly, an archaeologist. It is this lastrole, that of the archaeologist, that has often been ignored. The archaeologicalperspective brings to the field of conservation an outlook and an appreciation of thearchaeological record and material culture that otherwise might not be considered.


It is important that conservation laboratories working directly with archae-ological projects concern themselves with processing material in its exotic as wellas mundane forms with a primary objective of providing basic archaeological data.While waterlogged archaeological material is being processed, the establishedpreservation techniques are used, and new procedures can be tried on unimpor-tant or numerous objects. In this way, new techniques can be developed. Thedetailed records on the treatments accorded artifacts make it possible to evalu-ate the treatment of each object over a long period of time. Artifacts treated bydifferent and new procedures can be evaluated immediately and after a lapse ofseveral years. Through these procedures more realistic evaluations can be madeand more insights obtained and important contributions made to conservationscience. When a conservator is responsible for conserving archaeological artifactsfrom marine sites, contributions are made to both archaeology and conservation.During the conservation of archaeological material from waterlogged sites, espe-cially shipwrecks in a marine environment, as much basic archaeological data canbe contributed by the conservator and the conservation laboratory analyses as thearchaeologist and the field excavations. For this reason, the conservation should beas thorough as possible.

References

Ambrose, W.R., “Stabilizing Degraded Swamp Wood”, ICOM Committee for Conservation (Venice,Italy: 4th Triennial Meeting, 1975).

Argo, J., “On the Nature of Ferrous Corrosion Products on Marine Iron”, Studies in Conservation 26(1981): 42–44.

Barkman, L.G., “Conservation of Rusty Iron Objects by Hydrogen Reduction”, in F.B. Brown (ed.),Corrosion and Metal Artifacts, Special Publication 479 (Washington, D.C.: National Bureau ofStandards, 1977), pp. 156–166.

Brill, R.H., “A Note of the Scientist’s Definition of Glass”, Journal of Glass Studies 4 (1962): 127–138.

Bryce, T., “Alkaline Sulphite Treatment of Iron at the National Musuem of Antiquities of Scotland.The Conservation and Restoration of Metals”, Scottish Society for Conservation and Restorationof Metals (Proceedings of the Edinburgh Symposium, 1979), pp. 20–23.

Baley, E.R., “Coatings and Encrustations on Lead Objects from the Agora and the Method Used forTheir Removal”, Studies in Conservation 2 (1955): 49–54.

Charalambous, D. and W.A. Oddy, “The ‘Consolidative’ Reduction of Silver”, in Conservation inArchaeology and the Applied Arts (London, England: The International Institute for Conservationof Historic and Artistic Works, 1975), pp. 219–228.

Cronyn, J.M., The Elements of Archaeological Conservation (London, England: Routledge, 1990).Farrer, T.W., L. Blek and F. Wormwell, “The Role of Tannates and Phosphates in the Preservation of

Ancient Iron Objects”, Journal of Applied Chemistry (1953): 80–84.Gilberg, M.R. and N.J. Seeley, “The Identity of Compounds Containing Chloride Ions in Marine Iron

Corrosion Products: A Critical Review”, Studies in Conservation 26 (1981): 50–56.Grattan, D.W. (ed.), Proceedings of the ICOM Waterlogged Wood Working Group Conference. Inter-

national Council of Museums Committee for Conservation, Waterlogged Wood Working Group,Ottawa, Canada (1982).


Grattan, D.W., “Waterlogged Wood”, in C. Pearson (ed.), Conservation of Marine ArchaeologicalObjects (London, England: Butterworths, 1987), pp. 55–67.

Grattan, D.W. and J.C. McCawley, “Conservation of Waterlogged Wood”, in C. Pearson (ed.),Conservation of Marine Archaeological Objects (London, England: Butterworths, 1987),pp. 164–206.

Green, V., “The Use of Benzotriazole in Conservation”, in Conservation in Archaeology and theApplied Arts (The International Institute for Conservation of Historic and Artistic Works, 1975),pp. 1–15.

Hamilton, D.L., Conservation of Metal Objects from Underwater Sites: A Study in Methods,Miscellaneous Papers no. 4 (Texas Memorial Museum, Austin, TX: Texas AntiquitiesCommittee, Publication no. 1, 1976).

Hamilton, D.L. Basic Methods of Conserving Undewater Archaeological Material Culture (Wash-ington, D.C., U.S. Department of Defense Legacy Resource Management Program, 1996).

Jensen, V., “Water-Degraded Organic Materials: Skeletons in our Closets”, Museum 137 (1983),pp. 15–21.

Jensen, V., “Conservation of Wet Organic Artifacts Excluding Wood”, in C. Pearson (ed.), Conser-vation of Marine Archaeological Objects (London, England: Butterworths, 1987), pp. 122–163.

Koob, S.P., “The Use of Paraloid B-72 as an Adhesive: Its Aplication for Archaeological Ceramicsand Other Materials”, Studies in Conservation 31 (1986): 7–14.

Lane, H., “Some Comparisons of Lead Conservation Methods, Including Consolidative Reduction”,in Conservation and Restoration of Metals (Proceedings of the Edinburgh Symposium, 1979),pp. 50–66.

MacLeod, I.D., “Conservation of Corroded Copper Alloys: A Comparison of New and TraditionalMethods for Removing Chloride Ions”, Studies in Conservation 32 (1987): 25–40.

Macleod, I.D. and N.A. North, “Conservation of Corroded Silver”, Studies in Conservation 24(1979): 165–170.

McKerrell, H.R.E. and A. Varsanyi, “The Acetone/rosin Method for the Conservation of WaterloggedWood”, Studies in Conservation 17 (1972): 111–125.

Mibach, E.T.G., “The Restoration of Coarse Archaeological Ceramics”, in Conservation in Archae-ology and the Applied Arts (London, England: The International Institute for Conservation ofHistoric and Artistic Works, 1975), pp. 55–61.

Moncrieff, A., “Problems and Potentialities in the Conservation of Vitreous Materials”, in Conser-vation in Archaeology and the Applied Arts (London, England: The International Institute forConservation of Historic and Artistic Works, 1975), pp. 99–104.

North, N.A., “Corrosion Products on Marine Iron”, Studies in Conservation 27 (1982): 75–83.North, N.A. and I.D. MacLeod, “Corrosion of Metals”, in C. Pearson (ed.), Conservation of Marine

Archaeological Objects (London, England: Butterworths, 1987), pp. 68–98.North, N.A. and C. Pearson, “Alkaline Sulphite Reduction Treatment of Marine Iron”, ICOM

Committee for Conservation (Venice, Italy: 4th Triennial Meeting, 1975), pp. 1–14.Oddy, W.A. and M.J. Hughes, “The Stabilization of Active Bronze and Iron Antiquities by the Use

of Sodium Sesquicarbonate”, Studies in Conservation 15 (1970): 183–189.Olive, J. and C. Pearson, “The Conservation of Ceramics from Archaeological Sources”, in Conser-

vation in Archaeology and the Applied Arts (London, England: The International Institute forConservation of Historic and Artistic Works, 1975), pp. 63–68.

Parrent, J.M., “The Conservation of Waterlogged Wood Using Sucrose”, Studies in Conservation 30(1985): 63–72.

Patscheider, J. and S. Veprek, “Application of Low-Pressure Hydrogen Plasma to the Conservationof Ancient Iron Artifacts”, Studies in Conservation 31 (1986): 29–37.

Patton, R. “The Conservation of Artifacts from One of the World’s Oldest Shipwrecks, the Ulu Burun,Kas Shipwreck, Turkey”, in J. Black (ed.), Recent Advances in the Conservation and Analysis ofArtifacts (London, England: Summer Schools Press, 1987), pp. 41–49.


Pearson, C., “The Western Australian Museum Conservation Laboratory for Marine ArchaeologicalMaterial”, The International Journal of Nautical Archaeology and Underwater Exploration 3(2)(1974): 295–305.

Pearson, C. (ed.), Conservation of Marine Archaeological Objects (London, England: Butterworths,1987a).

Pearson, C., “Conservation of Ceramics, Glass, and Stone”, in C. Pearson (ed.), Conservation ofMarine Archaeological Objects (London: Butterworths, 1987b).

Pearson, C., “Deterioration of Ceramics, Glass and Stone”, in C. Pearson (ed.), Conservation ofMarine Archaeological Objects (London, England: Butterworths, 1987c), pp. 99–116.

Pearson, C., “The Use of Polyethylene Glycol for the Treatment of Waterlogged Wood – Its Pastand Future”, in Conservation of Waterlogged Wood (Netherlands National Commission forUNESCO, 1979), pp. 51–56.

Plenderleith, H.J. and A.E.A. Werner, Conservation of Antiquities and Works of Art. Revised Edition(London, England: Oxford University Press, 1977).

Sease, C., “Benzotriazole: A Review for Conservators”, Studies in Conservation 23 (1978): 76–85.Selwitz, C., “Cellulose Nitrate in Conservation”, Research in Conservation 2 (The Getty Conserva-

tion Institute, 1988).Singley, K., The Conservation of Archaeological Artifacts from Freshwater Environments (South

Haven, MI: Lake Michigan Maritime Museum, 1988).Tylecote, R.F. and J.W.B. Black, “The Effect of Hydrogen Reduction on the Properties of Ferrous

Materials”, Studies in Conservation 25 (1980): 87–96.UNESCO, The Conservation of Cultural Property with Special Reference to Tropical Conditions

(Paris, France: UNESCO, 1968).Watson, J., “Suitability of Waterlogged Wood from British Excavations for Conservation by Freeze-

Drying”, in J. Black (ed.), Recent Advances in the Conservation and Analysis of Artifacts(London, England: Summers Schools Press, 1987), pp. 273–276.

Weisser, T.D., “The Use of Sodium Carbonate as a Pre-Treatment for Difficult-to-Stabilize Bronzes”,in J. Black (ed.), Recent Advances in the Conservation and Analysis of Artifacts (London,England: Summers Schools Press, 1987), pp. 105–108.

conservation of cultural materials from

Documents