managing change: preserving history

ISSN:1369 7021 © Elsevier Ltd 2007APRIL 2007 | VOLUME 10 | NUMBER 450

The paintings, books, documents, and other riches found in our

museums, libraries, and archives appear for the most part to be

relatively inert and statically fixed in time and place. In reality,

this is an illusion: slowly over time the many materials used to

make these artifacts inevitably change and degrade, leading in

some cases to considerable loss of information and value. The

changes in materials in such collections can take tens, hundreds,

or even thousands of years and in some cases can be

imperceptible to the naked eye. These changes also affect

modern digital storage materials such as CDs and DVDs and

in some modern materials, such as plastics or synthetics, the

changes can be very rapid and the associated irreparable loss of

information and value rapidly becomes significant. Unfortunately,

for example, many important 20th century works of art made

from polymer-based materials have already shown significant

signs of decay. It is essential in all cases that we understand the

degradation processes at play and take steps to minimize them.

Here we will explore how science and technology are helping us

manage the changes in the materials that make up our cultural

heritage.

Much of our cultural heritage is preserved in museums, libraries, and archives and the artifacts therein give us unique insights into the lives of people long gone and methods of working with materials long forgotten. We describe a few of the riches to be found in the collection of The National Archives, UK. We identify some of the decay processes that are at play and show how modern scientific tools allow us to study the mechanisms and kinetics of these decay processes. Also, we discuss how conservation ethics and the associated constraints on sampling make the study of these artifacts particularly challenging. Ultimately, of course, the collective aim of scientists, curators, and conservators is to understand the fabrication of these objects better and to find the best conditions for their storage and display in order to preserve them for future generations.

Nancy Bell1* and David McPhail2

1*The National Archives, Kew, Richmond, Surrey, TW9 4DU, UK

2The Materials Department, Imperial College, London, SW7 2AZ, UK

1*E-mail: [email protected]; 2e-mail: [email protected]

Managing change: preserving history

mailto:[email protected]

mailto:[email protected]

APRIL 2007 | VOLUME 10 | NUMBER 4 51

Many different words are used to describe the interventions used

in this complex and multifaceted area. The terms ‘conservation’,

‘preservation’, and ‘sustainability’ are commonly used, for example,

and represent different aspects of the process of managing change.

‘Conservation’ is usually narrowly defined and involves active

intervention with objects to ensure chemical and physical stability

through a specific treatment or repair. In contrast, ‘preservation’ is

more holistic and involves mitigating the physical and chemical risks

to artifacts in order to prevent or retard decay. Clearly, it is important

to manage the change in objects as best we can but at the same time

allow access. Achieving a balance between access and preservation

involves, on the one hand, making our cultural heritage available to

the public, for example by placing exhibits in display cases, and, on the

other hand, ensuring its preservation for future generations to study

and enjoy, i.e. maximizing both the artifacts’ survival and accessibility1.

This is a very difficult task and is made even more so because we can

seldom rely exclusively on a single technique, approach, or model.

However, in more recent years, the potential of science and technology

to help ‘manage change’2, that is to retard decay and deterioration

in cultural artifacts, has been recognized. Indeed, a wide range of

scientific disciplines including materials science, chemistry, engineering,

and environmental science now have an important role to play in

identifying and solving collection-based problems.

Science has always had an important role to play in the

interpretation and preservation of material culture. Modern

analytical tools also allow us to conduct a detailed inspection of the

microstructure of materials. This in turn reveals further dimensions to

the materials employed and the technology used to create the object

(Fig. 1). Analytical testing also has an important role to play in the

interpretation of artifacts and, rather like forensic analysis, is being

used to explore questions of authorship or authenticity.

Scientific and technological research is also helping us to decide

how best to display and store artifacts, as there is always a dynamic

interaction between the object and the environment around it. For

example, textiles and adhesives commonly used inside display cases

are routinely tested to ensure that they will not produce an adverse

reaction if they come into contact with the artifacts on display. If

objects are not kept in optimum conditions, decay mechanisms are

sometimes accelerated. Materials expansion and contraction arising

from variations in humidity and temperature will cause paint layers to

dislodge, while unchecked light levels will soon fade textiles and light-

sensitive photographic images, prints, and drawings.

Conservation scienceConservation science, termed ‘heritage science’, is a field of activity

that has emerged in the last three decades. Conservation science brings

together science, conservation, and heritage under one rubric and is,

therefore, a discipline operating in the area where the sciences, arts,

and humanities overlap. For some years, conservation science has been

viewed as an adaptive science, where scientists working in other fields

have brought expertise to this domain. As the discipline has evolved,

however, it has attracted a new breed of scientists working exclusively

in this arena who are developing tools and methods appropriate to

conservation, as well as supporting pure research, and thus developing

a distinct new brand of science3.

Working in the heritage science sector is fascinating, and while

the objects we study and problems we face are always engaging,

there are very distinct challenges. For example, we generally have

little or no information about the materials and techniques that were

used to make the object. The provenance of the materials used is

often unknown and the environmental history, including previous

conservation treatments, is sometimes undocumented. The materials

will often be a complex mixture of crystalline and glassy phases

containing defects and voids, and the surfaces will often be crazed

and cracked (Fig. 2). Often the objects are multilayer composites

Fig. 1 Detail of a 16th century illumination of Cardinal Wolsey (Magdalen

College, Oxford, Ms. 223). Illuminations were used as illustrations in

manuscripts/books before the age of printing. This exacting miniature artwork

was executed on parchment using finely ground pigments held in a binder such

as gum arabic and applied with a very fine brush. Here we see the lively hand of

the illuminator at work, with pencilled under-drawing still visible underneath

the thin blue washes applied in the sky area. In contrast, other elements of the

image are rendered with thickly applied pigment. Expensive gold pigments add

shading and richness. Understanding the process and the types of materials

used to execute works of art is central to the work of conservators. Noninvasive

analysis of the materials, e.g. pigments, informs our understanding of how

objects were made and used.

Managing change: preserving history APPLICATIONS

APRIL 2007 | VOLUME 10 | NUMBER 452

of materials: for example, photographs contain materials based on

cellulose and proteins, while DVDs contain equally complex layers

of materials such as polycarbonates, acrylic lacquers, and dyes. The

complexity of these structures and the lack of knowledge often

surrounding them present us with a challenging detective story that we

need to unravel using all the evidence available together with state-

of-the-art scientific analysis tools (Fig. 3). This situation is in sharp

contrast to that presented by a modern silicon wafer, where we have

an almost complete knowledge of all aspects of the microstructure,

processing, and properties. And, unlike other scientific research based

on destructive sampling, conservation science is firmly situated within

an ethical framework precluding the sampling of objects. Historically,

this has limited the application, for example, of destructive analysis

techniques and those involving the application of a vacuum to samples.

Approaches to analysis in conservation scienceRecent advances have involved the development of a range of

microinvasive or noninvasive technologies and these are making a new

Fig. 2 Materials science and engineering is concerned with the relationship between microstructure, processing, and properties. The study of materials in collections

such as The National Archives is particularly challenging because of the lack of knowledge about the raw materials, the processing conditions, and the environmental

history of the artifacts, together with the consequent complexity of the microstructure.

Fig. 3 This micrograph (25x) shows the (surface) of a pigment layer as found in the drapery of the figure in the lower left corner (Fig. 3a). X-ray fluorescence

(XRF) confirmed the presence of both azurite and ultramarine pigments. Often these two pigments were used in combination for reasons of economy without

compromising the visual impact. (a) Detail from the Annunciation (Magdalen College, Oxford Ms. 223).

APPLICATIONS Managing change: preserving history

(a)

Properties

Processing Microstructure

MaterialsScience


range of analyses possible. Usually a hierarchical approach to analysis

is used, starting with noninvasive techniques such as optical and

optical interference microscopy. For example, the Zygo® white light

interferometer yields digital maps of surface morphology (Fig. 4) and

can be used to monitor the evolution of topographical features as a

function of time4. Such optical techniques are air-based, noncontact,

and have an open architecture so that whole objects may be inspected;

indeed, the apparatus can usually be taken to the object itself.

The next set of techniques is more sophisticated, but also air-based

and nondestructive. Raman spectroscopy is one technique that can

be used to identify organic pigments and Fourier transform infrared

spectroscopy attenuated total reflection (FTIR-ATR) is now routinely

used in many conservation studies for materials identification (Fig. 5).

Particle induced X-ray emission (PIXE) is another chemical analysis

technique with parts-per-million sensitivity in favorable cases. PIXE can

be operated with the object in air a few millimeters from a vacuum

window and has been used for a wide range of studies spanning

archaeometry and conservation5. PIXE can also be operated with a

sample from the object under vacuum and in this case a better lateral

resolution may be achieved. PIXE only introduces a modest level of

damage, which is seldom perceptible to the naked eye (Fig. 6). The

environmental scanning electron microscope (ESEM) embraces similar

concepts to avoid the damaging effects of high or ultra-high vacuum.

SEM energy dispersive X-ray spectroscopy (EDX) has proved a highly

useful technique to distinguish between corrosion products and

manufacturing impurities6.

There are other techniques that are only used if the information

they produce is essential, for example techniques that require a small

sample to be removed from the object being studied and/or that

consume the sample as the measurement is taken. Sometimes analysis

has to be conducted in a high or ultra-high vacuum, which is also

undesirable as the vacuum can produce irreversible reactions associated

with out-gassing and dehydration. Such analyses would be the last to

be conducted and indeed should only be initiated if the information

is essential, preferably using didactic material. While destructive

vacuum-based analytical techniques are far from ideal for cultural

heritage studies, they have the power to reveal information at very

high resolution and sensitivity. For example, using secondary ion mass

Fig. 4 The Zygo® microscope operates on the basis of white light interferometry and generates a digital map of the topography of a surface. The instrument is air-

based and has a large sample stage suitable for the imaging of a wide variety of objects. The example shown is an image of a cover glass for a container. The glass

has undergone atmospheric corrosion, moisture has penetrated the glass and alkali ions have migrated out to the surface where they have reacted with atmospheric

gases to form sulfates, carbonates, and formates.

Fig. 5 A letter written by an individual purporting to be Jack the Ripper. [The

National Archives, UK MEPO 3/142 (253).] FTIR-ATR analysis was used to

identify the smudges on this letter that were once thought to be blood but

are now thought to be an etching ground. [MEPO3-142 Pt. 2 (253), October

1888.]



spectrometry (SIMS) depth profiling it is possible to measure ultra-

slow reaction rates proceeding at less than 1 nm per day, equivalent

to a millimeter of decay every 3000 years (Fig. 7). For sputter depth

profiling, an area typically 100 µm x 100 µm has to be analyzed to

a depth of a micron or so. SIMS also has the sensitivity to measure

changes in surface composition at the level of a part per million thus

obviating the need for accelerated aging experiments in this system,

and therefore detecting changes long before they become visible to

the human eye7.

Conservation science research at the National ArchivesThe National Archives (TNA)8 is the UK government’s official archive,

containing 900 years of history from the Domesday Book to the present

day, with records ranging from paper and parchment scrolls to recently

created digital files and archived websites. The collection is very

diverse and, while many may be familiar with national treasures such

as the Domesday Book (compiled in 1086) or Magna Carta (1215), less

familiar objects include curiosities such as the photographs of foremost

Fig 7 Ultralow-energy SIMS depth profiling can resolve the positions of atoms beneath the surface of a material with subnanometer precision. In this example,

four identical glass samples have been aged at room temperature for different periods of time under 55% relative humidity and SIMS has been used to monitor

the sodium in the glass. The near surface of the glass has lost sodium to the surface and the longer the aging process the greater the amount of sodium that has

been lost. The significance of this approach is that corrosion kinetics can be studied without the need for accelerated aging. This experimental methodology can be

combined with isotopic labeling where appropriate (e.g. D2O) and is transferable to a wide range of archive materials where ultra-slow corrosion processes are at

play. (Data courtesy of Sarah Fearn, Imperial College London.)

Fig. 6 PIXE microbeam images of the cross-section of a photograph. PIXE and Rutherford backscattering are used at the Surrey University Ion Beam Centre13 to

identify and quantify elements in photographic emulsions and backing paper. (Courtesy of Geoff Grime, Inma Gomez-Morilla, Chris Jeynes, Surrey Ion Beam Centre.)



British 19th century photographer Eadweard Muybridge (Fig. 8), whose

seminal studies on animal locomotion and zoetrope design led to the

development of motion picture film and cinematography.

Preserving the national memoryPreserving both an analogue and digital collection the size and scale

of TNA, with some 178 km of shelving and well over 10 million items,

is, in the first instance, about mitigating risk factors – an important

first step in any preservation program. The major risk factors to any

collection will vary according to the materials from which the object is

made and the mechanisms and kinetics of the decay processes, which

are inextricably linked to heat, water, light, and the action of gases

such as oxygen and sulfur dioxide. Clearly, it is essential to conduct a

systematic assessment of the risks to the objects in the archive before

one can sensibly decide how to manage the collection. Therefore,

TNA has embarked on a three-year risk assessment program following

models first developed by Robert R. Waller of the Museum of Nature in

Canada9.

TNA has for some years taken its responsibility for preserving

the collections seriously. In recent years, however, as the potential

of science to inform preservation policies and practice has been

appreciated, it has been deemed necessary to establish conservation

research formally. Currently, the primary focus of the research

program is concerned with developing an in-depth understanding of

the physical and chemical profile of materials, including parchment,

photographs, and some modern records made of plastics and

synthetics. Understanding the deterioration mechanisms in play and,

most importantly, the rates of decay of specific groups of materials

is imperative to achieving the main objective of reducing or slowing

deterioration. Moreover, an evidence base of how and when materials

degrade informs when resources or methods for reducing deterioration

should be put in place – in other words, managing change. The second

area of TNA research is directed toward technical examination, defined

as the use of scientific analysis to determine what objects are made of,

when, and how. Technical examination can add a historical dimension

and improve our interpretation of the collection.

Unfortunately, the limited resources available in the cultural

heritage sector preclude support for large numbers of scientists working

in state-of-the-art facilities. While dedicated research facilities able

to take a long-term approach to collection stewardship do exist, this

activity in the UK is largely concentrated in national museums but

seldom in libraries or archives. The importance of in-house expertise

to deliver practical and preventive conservation science, as well as to

improve our understanding of collections, cannot be overestimated.

Nevertheless, new streams of funding from the public and private

sectors are proving a useful catalyst for collaborative partnerships

with other cultural institutions and university science departments to

further extend our problem-solving capacity. Thus, TNA is developing

collaborative opportunities to investigate fundamental materials

science questions that will help us understand mechanisms and rates of

decay better.

A closer look at the Domesday BookUsing recent advances in noninvasive and microinvasive analytical

testing, a major interdisciplinary project has been launched to study the

Domesday Book (Fig. 9). In partnership with the School of Optometry,

Cardiff University, and specialists from the School of Conservation,

Copenhagen, our goal is to learn more than previously possible about

the making and meaning of this icon using a hierarchy of techniques

from the visual to the nanoscopic. Optical microscopy techniques are,

as a first step, enabling comparative analysis of the parchment used as

the writing support and a range of complimentary techniques, including

Fig. 8 The experiments of Eadweard Muybridge (1830-1904) in rapid action

photography are landmarks in photographic history. [COPY1-389(ii) f.58a

Bucking horse, by E. Muybridge, 1887.]


Fig. 9 Great Domesday, TNA. Great Domesday is made of 383 parchment folios

(~20 x 14.5 inches mm). The surface of the skin would have been smoothed

in preparation for writing. It is thought the text was written with a quill pen,

using ferro-gallo-tannate ink typical of the period. [E31-2-1 Great Domesday,

Wiltshire - Dorset 75.]


amino acid testing, are helping us to determine conclusively the species

of animal skin. Using just a few fibers of parchment, simple shrinkage

temperature testing gives us an indication of the deterioration of the

collagen present10. At the other end of the analytical spectrum, X-ray

diffraction performed at the European Synchrotron Research Facility is

being used to determine the structural integrity of the collagen11. It is

envisaged that the results will help to determine the condition of the

collagen, which will help us to monitor changes and calibrate current

standards of display and storage of the Domesday Book.

Photographs – behind the image Emerging technologies are also enabling fascinating and important

studies of cultural heritage, particularly when used in conjunction with

documentary sources. The interplay of art, technological, and economic

history is opening new avenues in our understanding of the processes

and materials used. While technical analysis has often been applied to

the study of paintings, analysis of other artifacts such as photographs

has yet to be fully exploited. Building on protocols established at the

Getty Conservation Institute12 and in collaboration with Imperial

College London, research is underway to understand the complexity

of photographic processes used in the last 150 years. The structures

are extremely complex multilayers and it has proved necessary to

sacrifice some small samples to yield a more complete understanding

of the system. Focused ion beam (FIB) milling has been used on small

areas to prepare cross-sections for subsequent analysis (Fig. 10). In

recent experiments, PIXE has been used to provide chemical maps of

a cross-section through a photograph (Fig. 6). The initial results have

been produced with the sample in vacuum, but it is planned to conduct

analyses on whole objects with the external beam. Another promising

technique is time of flight (TOF) SIMS.

Future workOver the last 30 years, the evolution of conservation science has

changed significantly the way we see, understand, and preserve cultural

heritage. Inevitably, future technological advances will catalyze new

thinking, inspire new approaches, and develop new science. Speculating

what changes lie ahead, or the impact they may bring, is always risky,

nevertheless the potential for creative collaborative partnerships between

disciplines to help us do things better is enormous and welcome.

There can be no doubt that advances in micro-invasive and noninvasive

materials analysis techniques will be of enormous importance to

conservation science, helping us to understand basic degradation

processes better and allowing us to monitor changes over time.

Conservation science provides a vital link connecting the material aspects

of the artifact to the hand that created it and the context that valued it.

The more we can understand what we see, the more we will value our

heritage and appreciate the importance of managing change .

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ldsctech/256/25602.htm)

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ldsctech/256/25602.htm)

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8. www.nationalarchives.gov.uk

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London (2002) 102, 100

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11. Kennedy, C. J., et al., Nano Lett. (2004) 4, 1373

12. www.getty.edu

13. www.surreyibc.ac.uk

Fig. 10 FIB secondary electron and ion images of a cross-section of a

photograph. The cross-section was prepared by ion beam milling but the

surface was first coated with a platinum bar to protect the material during this

procedure. The secondary electron and secondary ion (total ion) images reveal

the different contrast mechanisms in these two modes of analysis and highlight

different aspects of the multilayer structure. (Courtesy of Richard Chater,

Imperial College London.)


http://www.publications.parliament.uk/pa/ld200506/ldselect/ldsctech/256/25602.htm




http://www.nationalarchives.gov.uk

http://www.getty.edu

http://www.surreyibc.ac.uk

managing change: preserving history

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