1982-introduction and summary

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ALAN D. FRANKLIN

National Bureau of Standards

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11

introduction

The seminar on Ceramics as Archaeological MaLen·

a!, of which these are the proceedings, was held at the

National Bureau of Standards and the Smithsonian

Institution, 29 September th rough 1 October 1980. It

was one of a continuing joint series by the Conserva

tion Analytical Laboratory of the Smithsonian and

the National Measurement Laboratory of the Bureau

of Standards on the general subject of the Applica

tion of the Materials and Measurement Sciences to

Archaeology and Museum Conservation.The seminar was intended not only to develop and

exemplify as much as possible the use of a materials

science approach to archaeological problems, but al

so to show the connection between those problems

and the way in which the technical studies are con

ducted. Although in the interest of clarity for a read

ing audience these proceedings are not arranged this

way, the seminar was planned around, and the result

ing papers do reflect, three areas of discussion: (1)

physical science studies whose ultimate goal is to re

veal information on ancient ceramic technologies and

the organization of ceramic production or to cast

light on the function of ancient ceramics; (2) studiesof composition, both chemical and mineralogical, or

other methods of "fingerprinting" the materials in

volved for the investigation of provenience, sources

of raw materials, and trade or exchange patterns; and

(3) standardization of the physical and chemical

measurements involved.

In presenting these proceedings, the editors felt

that a logical arrangement for the volume would be

by material and by disciplinary approach; the table

of contents reflects this. While the seminar by no

means exhausted its subject matter, the editors hope

that it did include some of the most significant work

now going on, an d that this volume will serve to

stimulate and to act as a reference for interdiscipli

nary studies that combine the efforts of physical and

archaeological scientists.

Summary

Archaeometric research involves the physical and

biological sciences applied to problems in archaeolo

gy. The research must be centered around archaeo

logically defined questions and must produce infor

mation that advances archaeological understanding

. In his paper, F. R. Matson states that "itis

essentialto ask the question, 'What is one trying to learn from

the study of ancient pottery?' " W. D. Kingery re

cords the need, in research on ceramics as archaeo

logical material, to address the questions of When,

Where1 How, By Whom, and Why a particula r cera-



mic was made. The Where, When, and Ho w involve

largely problems in characterization an d material

science study of the ceramic as a material. Study of

these problems, once defined within an archaeologi

cal context, is an appropriate activity fo r a physical

scientist or measurement specialist working closely

with archaeologists. An example might be the work

of a chemist who determines the elemental composi

tions of ceramics in an effort to define relations

among them, relations that in turn might shed lighton their origins or on mechanisms of trade and ex

change. Another example is a materials scientist

studying physical properties that in turn may give

clues to the firing conditions under which the ceramic

was formed.

Why and By Whom involve problems of process

and function. No t only do these have a much more

strongly anthropological character, but also they in

volve questions of ceramic technology, a familiarity

with how and why ceramics have been prepared in

general, and how the process interacts with the final

properties. These proceedings deal mainly with the

questions of When, Where, and How; however, thequestions of Why and By Whom were to some extent

considered in the discussions during the seminar. In a

general way, it was recognized that the active partici

pation in archaeometric research by ceramic tech

nologists, people familiar with ceramic production

processes and ceramic function, is relatively rare an d

should be encouraged.

Problems of Characterization and Materials Science

Studies

The seminar was organized to concentrate on the

physical problems of interpreting ceramics. Th e in

terpretation of material residues found at archaeological sites, however, requires the participation of

other scientists, such as ethnoarchaeologists, as well.

The archaeometric study of ceramic specimens in

volves characterizing the specimens with respect to

chemical composition, physical properties, and

microstructure, along with the examination of stylis

tic details, in order to discern with as much certainty

as possible relations among the specimens. In this

way it is hoped to determine the source clays from

which a set of specimens was made, or determine that

various sets of specimens are products of the same

workshop or potter and therefore probably can be

used to delineate exchange mechanisms. As Kingery'sanalysis suggests, the credibility of the relations de

dL!ced can be increased in a number of ways. One is

to include data of very different sorts, such as chemi

cal composition together with microstructure and

stylistic detail. A second is to work with specimens of

weU-known provenience, thus bringing to bear as

12

much archaeological information as possible. A thi

is to quantify the observations an d make the me

surements as accurate as possible. This was th e su

ject of the paper by De Atley, Blackman, an d Oli

who investigated the problems involved in using ele

tron microprobe analysis for quantitative bu

chemical analysis of ceramics. Finally, the base of th

comparisons should be made as broad as possibl

This last point was discussed in detail by Lemoi

an d Picon, who pointed out the need fo r a local ne

work or data base on all the possible sources, or

least the most probable ones, when trying to loca

the origins of a given ceramic. This in turn sugges

the very great value of absolute measurements, or

least measurements made in all laboratories relati

to the same standards, so that measurements fro

one laboratory are interchangeable with those

other laboratories. By this means the data base f

one study by one laboratory may be expanded by u

ing data from the others.

The paper of G. Harbottle addressed the questi

of standardization and interlaboratory comparis

for chemical characterization by neutron activati

analyses. The use of common standard reference m

terials by all laboratories would be ideal and may

necessary if precision levels of 5 percent or better

the concentrations of significant elements are r

quired by the archaeological problems. In additio

joint studies by several laboratories of cases of pa

ticularly serious disagreement may be needed

achieve this level of agreement. The difficulty at th

moment is that no fully certified common standar

have been available. Several laboratories ha

created working standards, e.g., the Asaro-Perlm

Pottery Standard and the six U.S. Geological Surv

Rocks used by Harbottle et al. at Brookhaven, an

agreement on their composition is gradually bein

reached. A great deal of work would be required

calibrate each laboratory's working standards wi

respect to a common certified standard, and th

practical utility of doing so is still very much a matt

of discussion. Adequate standards for other me

surements are also lacking. Compendia of ceram

microstructures, especially for scanning electro

microscopy, could be very valuable. An examp

might be the microstructure of calcite reformed b

hydration and carbonation of primary calcite decom

posed during the firing process. The range of usef

patterns could be very large, but a trial collection operhaps 50-100 was suggested as a test.

In a somewhat parallel vein, it is not always ap

preciated that all measurements contain a bi t of un

certainty. Not only must the archaeologist recogniz

this uncertainty in the archaeometric data with whic

he is provided and temper his expectations and inte

Alan D. Frank !



pretations accordingly, but also the archaeometrist

has a responsibility to ascertain the uncertainty and

to report it with the data.

In addition to recognizing the limits of precision

inherent in physical measurement, it is also necessary

to recognize the limits to absolute knowledge of a

given class of ceramics imposed by sampling. No

given collection of pieces or sherds can ever be stated

to "represent" a class of ceramics in the sense that a

random sample properly selected from the total

population of such sherds would. Every archaeological collection must be presumed to have some un

known bias. I t is a perfectly valid procedure to com

pare properties of two archaeological collections us

ing statistical tests - such as Student's t-test for

means or the F-test for variances- and to conclude

that at a certain confidence level the collections do

not represent randomly drawn samples from the

same normally distributed population. It must be

kept in mind, however, that the reasons why they do

not may always include, not that they are not drawn

from the same population, but that they were not

randomly drawn, owing to the uncontrollable acci

dents in the archaeological processes of assemblingthe collections. Furthermore, there is no guarantee

that the population is normally distributed. Such

problems were considered in the paper of Lemoine,

Walker, an d Picon and the ensuing discussion. The

fact that the chemical analyses are usually made on

only a very small specimen taken as inconspicuously

as possible from the piece or sherd accentuates the

problem, since ceramics are often not very homogeneous.

Th e firing processes used by the potter con

tribute to the ceramic's microstructure, bu t other

variables as well have important effects. The role of

calcium in the development of the microstructu re received particular attention in this seminar, especially

in the papers of Maniatis et al., Tite et al., an d Stim

mel et al. Tite et al. developed in detail the apparent

control exercised in Greek Attic pottery and Roman

terra sigillata over the porosity of both body an d slip.

The slip was rendered dense and impervious by the

use of a noncalcareous clay, while the body was made

porous an d open in structure by use of a calcareous

clay. Chemical analysis of the clay fractions using the

electron microprobe showed some change in concen

tration of elements other than calcium in going from

body to slip. Tite felt the calcium carbonate involved

was an integral part of the clays rather than added infinely ground form, since he has found in separate

experiments that finely ground calcium carbonate

was ineffective in producing the open structure. The

possibility was considered in the discussion that the

difference in calcium content might have resulted

from levigation of a single clay, with the slip being

Introduction and Summary 13

produced from the fine fraction and the body from

the heavy. Harbottle and R. B. Heimann both report:

that this possibility is discussed in forthcoming publi

cations.

Calcareous clays produce these open-structured

high-fired ceramics even though carbon dioxide re

lease is over before serious vitrification begins. Tite

suggested that the carbon dioxide release separates

the particles of the various minerals forming an open

structure which is then captured by the cementing

action of the vitrification.Tite noted that the impervious nature of the slip on

the Greek Attic pottery might account for the failure

of the iron ions in the slips to reoxidize during the

final, oxidative phase of the ancient firing schedule,

whereas the iron in the porous body would reoxidize.

This suggestion, which would account for the black

slip on a light-colored body, first appeared as the

explanation of how the black and red glazes were

achieved on Attic painted vases in the book by

Joseph Noble, The Techniques of PaintedAttic Pot-

tery, in 1965. Tite suggested that this might not be the

whole story, however, since the red slip on Roman

terra sigillata was observed to reduce readily, but toreoxidize only with difficulty. In noncalcareous

clays, as in the slips, the iron oxides in the reduced

state may form magnetite, which is difficult to oxi

dize, whereas in the presence of calcium, iron-bear

ing silicates are formed and these reoxidize readily.

Maniatis invoked exactly the same explanation to

account for the difference in behavior of calcareous

versus noncalcareous clays with firing in Mossbauer

experiments. The noncalcareous clays appeared to

form large particles of ferric oxides when fired in air,

whereas the calcareous clays did not.

Stimmel et al. also use the notion of the open struc

ture produced in fired ceramics by the presence ofcalcium to explain why the use of burnt shell temper

in North American Indian pottery did not result in

popping, even though the firing temperature ap

parently exceeded that at which calcium carbonate

decomposes.

The determination of the firing conditions,

especially temperature, was one of the major themes

of the seminar. Matson pointed out that an interna

tional meeting was held in Berlin during 1977 on

"Ceramic Firing Techniques and their Determination

through Experimental Archaeology." Papers by

Maniatis an d Tite dealt with specific techniques for

determining firing temperatu res.In general, two methods are used. The sherd may

be examined and its properties compared to a series

of similar materials fired at various temperatures.

These standards form a sort of temperature scale,

an d the unknown's place is found along the series.

Alternatively a structure-sensitive property or prop-



erties may be monitored while the sherd is reheated,

and the firing temperature derived from the discon

tinuity observed when the original firing temperature

is reached and the structure begins to change. In both

cases, the firing atmosphere and firing time, or rate,

can influence the results and since these conditions

during the original firing are unknown, an undeter

minable uncertainty is introduced. Also, changes oc

curring during burial can produce false estimations

of the firing temperatures.

Problems ofFunctions and Process

A few problems involving archaeological inferences

upon archaeometric data were very briefly con

sidered in the discussion periods. These topics in

clude the nature of firing chamber s used and the vari

ability of output from a given facility; the study of

workshops in economic terms; and the historical

study of the development of ceramic technology.

The uncertainty in a firing temperature as deter

mined by either method described above appears to

be at least 50 o to 100 °C, about the same as the varia

tion to be expected within a kiln or other firing cham

ber. For the purpose of distinguishing whether thepottery was fired in a bonfire or in a kiln, this present

accuracy appears adequate. On the other hand, the

variability within a given production facility may be

of archaeological concern so that increased accuracy

may be useful. At present the determination of a fir

ing temperature is a fairly cumbersome process, and

it may not be feasible to do enough specimens to

make a study of variability possible.

The unfolding of the historical development of

ceramic technology in a given cultural setting is of

considerable archaeological interest. Development

with both time and place should be amenable to

study, given a broad enough area within which to

work. Such studies involve familiarity with ceramic

technology, its uses and functions, and its underlying

science. Kingery gave as an example the fact that in

the nineteenth century new refractories appeared,

chemically basic in nature. I t would be difficult to

understand this development and how it came about

without realizing that the rapidly developing steel in

dustry needed refractories that would not decompose

in contact with basic slags, as do silicate-rich, clay

based acidic refractories. Here there is an interaction

of historical development with deliberate problem

solving, and chemical as well as archaeological ques

tions are involved.

14

Patterns ofResearch

A number of questions concerning the way archae

metric research is managed or done were considere

The work of Robert Snyder (see "The Rebirth of X

ray Powder Diffraction," New York State College

Ceramics Technical Report, no. 144, 1980) exemp

fies the way computers are being used, or ca n

used, to improve vastly the quality and amount

data that can be obtained for archaeometric studie

Computers can take and process data more rapid

than the human hand, and so increase the quantiand reduce the time. Computers can make instr

mental corrections and compare masses of data o

jectively to mathematical and statistical function

and so increase the precision. Computers can m a kmany repeat determinations, improving the ratio

signal strength to noise, and so improve the sensiti

i t ~ . Relatively inexpensive desk-top minicomputer

with great program flexibility, are available an d ca

often be dedicated to several experiments simult

neously, an d many kinds of microprocessors exi

which can be built into specific pieces of equipmen

I t is a reasonable guess that almost all physical mea

urement of any sophistication will be done in thway a very few years from now.

By its nature, archaeometry is an interdisciplina

activity. With regard to ceramics, there is need t

combine the talents of archaeologists, ceramic tech

nologists, an d materials scientists drawing on chem

istry, physics, and mathematics. Two sorts of collab

orations can be envisaged. In one, the design an

operation of the research program is carried ou t by

team involving such combinations, preferable alway

with the archaeologist at the center. In the other, be

cause so many valuable measurements are now avai

able that are possible only with large, expensiv

equipment, at least some of the research is done alarge national facilities where the active collaboratio

of specialists in the use of the facility is necessary

The example that comes to mind is the use of chem

ical analysis by neutron activation. Very effectiv

collaborative teams have been operating at a numbe

of major research reactors. The same kind of patter

will probably have to develop around other large

scale facilities, such as various types of electro

m i c r o . s c o ~ e s , sophisticated forms of elemental analy

ses usmg IOn and electron-beam excitation, X-ray dif

fraction, particularly with high-intensity sources an

perhaps a high-t emperature capacity, and so forth.

.In these interdisciplinary teams, two participantm1ght always be necessary, one the archaeologist

whose expertise defines the problem, and the other a

new specialist, expert in the interpretation of cerami

artifacts. This latter person will need a solid back_

Alan D. Frankli



ground in materials science and a good knowledge of

ceramics and ceramic technology, and enough

archaeology to connect the ceramic science to the

archaeological problem. Training for such people

scarcely exists now and cleaFly represents a challenge

to the universities concerned with archaeological

science.

The successful conduct of research of this kind,

combining archaeology with materials science at an

advanced level, will also require some adjustment on

the part of agencies providing support for university

research. I t represents an application rather than a

development of materials science and as such is diffi-

cult to consider as the responsibility of the materials

science community. I t is considerably more expensive

than th e archaeological community is used to, and is

generally thought to be beyond the means of that

community. If, however, the power of materials

science is to be made available to archaeological sci-

ence, some form of a rapprochement between these

extremes will have to be made.

Introduction and Summary 15

1982-introduction and summary

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