Reviewed by Charles C. Kolb, Division of Preservation and Access, National Endowment for the Humanities, 1100 Pennsylvania Ave. NW, Washington, DC 20506 USA
Pollard, Professor and Head of the Department of
Archaeological Sciences at the University of Bradford, is a recognized
authority on the application of chemical techniques to archaeological problems.
Heron, Lecturer in Archaeological Sciences at Bradford, specializes in
organic analysis, gas chromatography and mass spectrometry, and chemical
and geophysical prospection. They have the appropriate credentials and
expertise to prepare this eloquent, highly informative and current synthesis
in which they consider some of the major techniques employed in archaeological
chemistry. This compelling and unique volume is designed as a treatise
for archaeologists who need current information about chemical techniques
and procedures and for physical scientists who are asked to analyze archaeological
materials.
The book provides essential background on the procedures
and the applicability of those techniques of particular value to provenance
studies of obsidian, ceramics, glass, metals, and organic materials such
as resins and amino acids. The reader should not confuse the bookís title,
organization, or contents with Gofferís Archaeological Chemistry (1980),
and the volume is dissimilar in scope to Hendersonís (1989) edited compendium.
Pollard and Heronís work is based upon the premise that archaeological
chemistry requires a thorough understanding of chemistry and archaeology,
and often related disciplines such as biochemistry and geochemistry. Published
only in a 390-page paperback edition by The Royal Society of Chemistry,
it contains ten chapters, five appendices, and a twelve-page subject index.
Each chapter has its own references (560 total entries), and the illuminating
narrative is supplemented by 97 figures and 21 tables. Chapters 3 through
9 focus upon specific categories of material culture and integrate raw
material occurrences, historic background on fabrication, and analytical
methods, accompanied by valuable case studies demonstrating that science
has and can play a significant role in archaeological studies.
In the ěForewardî Colin Renfrew points out that
archaeological science is a discipline which is growing rapidly in scope
and maturity because of an advancements in scientific procedures and an
increased awareness of the problems of interpretation. The initial chapter,
entitled ěThe Development of Archaeological Chemistryî (19 pp., 63 references),
provides a brief historical context for the subsequent chapter, ěAnalytical
Techniques Applied to Archaeologyî (61 pp., 92 references), a largely non-mathematical
summary of some of the many analytical techniques used in modern archaeological
chemistry. Each subsequent chapter presents an historical perspective and
some of the underlying science of the techniques selected.
In Chapter 2, the authors consider atomic structure,
analytical spectroscopy, procedures, considerations (multi-elemental analyses,
quantitative versus qualitative uses), alternative analyses, and problems
(detection limits, element enrichment by the burial environment, etc.).
Optical Emission Spectroscopy (OES), now largely outmoded, older and newer
instrumentation in Atomic Absorption Spectrometry (AAS), and Inductively
Coupled Plasma Emission Spectrometry (ICP-AES), which has begun to replace
AAS for multi-element analyses, are detailed. They also characterize Inductively
Coupled Plasma Mass Spectrometry (ICP-MS) and Laser Ablation Inductively
Coupled Plasma Mass Spectrometry (LA-ICP-MS).
Techniques using X-rays, including Auger Electron
Microscopy (AES), X-ray Fluorescence (XRF), X-ray Photoelectron Spectroscopy
(XPS or ESCA [Electron Spectroscopy for Chemical Analysis]), and Energy
Dispersive X-ray Fluorescence (EDXRF) are delineated. The authors report
that Wavelength Dispersive X-ray Fluorescence (WDXRF) has relatively little
applicability to archaeological materials except ceramics. Analytical Electron
Microscopy (AEM), Transmission Electron Microscopy (TEM), and Particle-
or Proton-induced X-ray Emission (PIXE) analyses are defined.
Although Neutron Activation Analysis (NAA) was developed
during the 1950s, it had by the 1980s become the standard analytical method
used for producing multi-element analysis at the ppm level and has major
applications in the study of coins and ceramics. Hyphenated techniques
such as Inductively Coupled Plasma Mass Spectrometry (ICP-MS) are seen
as especially useful in environmental applications to measure isotopes
of heavy elements in plant materials and body fluids. Thermal Ionization
Mass Spectrometry (TIMS) is only mentioned.
Chromatographic techniques - gas or liquid chromatographic
(GC or LC) for organic and biological material - developed rapidly over
the past several years. There is also a wide range of hyphenated techniques,
including CG-MS and LC-MS; High Performance or High Pressure Liquid Chromatography
(HPLC) is the most commonly used form of the latter. Other techniques include
infrared and resonance procedures such as Infrared Microspectroscopy (IR),
Electron Spin Resonance (ESR), Nuclear Magnetic Resonance (NMR), Thermogravimetry
(TGA), Differential Thermal Analysis (DTA), and Differential Scanning Calorimetry
(DSC).
Chapter 3, ěObsidian Characterization in the Eastern
Mediterraneanî (23 pp., 56 references), elucidates how source attribution
of archaeological materials might be confirmed on the basis of chemical
composition. The origin and formation of several forms of obsidian (trachitic
obsidian is not discussed), and classifications (peralkaline, calcalkaline,
calcic, and alkaline) are elaborated. A case study concerns the sources
located in the eastern Mediterranean and neighboring regions, and employing
petrographic thin section studies, trace element analyses, wet chemistry,
OES, and NAA. Although a wide array of other analytical, geochemical, dating,
and magnetic approaches have been used, NAA and XRF are by far the methods
of choice, although Fission Track Dating may be used to determine the age
of the flows. There is a critical need for additional research on the intensity
of magnetization, saturation magnetization, and low field susceptibility
in order to delineate parent obsidian flows. The primary aim of obsidian
provenance studies is to assess economic and social factors underling the
movement of materials. The authors demonstrate clearly why obsidian characterization
has been one of the most successful applications of archaeological chemistry.
In Chapter 4, ěThe Geochemistry of Clays and the
Provenance of Ceramicsî (45 pp., 51 references), the authors elucidate
the structural chemistry of clays; review the basic structure of silicate
minerals, silicate mineral groups and classification, clay minerals and
deposits; and firing behavior, dehydration reactions, and phase diagrams.
The general principles of trace element geochemistry are considered, and
they comment appropriately that the chemical and mineralogical alteration
of the ceramic in its burial environment are largely unappreciated in provenance
studies. Problems of the natural variability of the clay beds, clay selection
and mixing, levigation and processing, the addition of temper, and the
firing cycle are noted. The representativeness of samples and assumptions
about quality controls employed in antiquity are seen as important variables.
NAA, XRF, and ICP-AES or ICP-MS are considered as appropriate analytical
techniques. There is an minimal consideration of thin section analysis
and ceramic petrology; for a comprehensive elucidation of chemical techiques,
readers should consult Jones (1986) and Neff (1992). The case study employs
specimens from Roman Britain and Gaul, using AAS and XRF studies to suggest
the provenance of Gaulish Rhenish wares and Trier terra sigillata.
Chapter 5, ěThe Chemistry and Corrosion of Archaeological
Glassî (47 pp., 78 references), begins with definitions of glass and the
structure and chemistry of archaeological glass. The section on the history
and chemistry of glazes is inadequate. The authors comment that ěthe traditional
archaeological view that colour can be simply related to the presence of
various ëcolouring agentsí can only be regarded as a very crude guideî
(p. 173). Coordination chemistry, crystal field theory, and redox reactions
are important aspects of glass analyses. The decay of Medieval window glass
is taken as a case study. IRRS (Infrared Reflection Spectroscopy), Infrared
Microspectroscopy, Auger Electron Spectroscopy, and ELS are used to determine
the composition of the surface layer, and analyses by XRD, AAA, and electron
microscopy are noted. The authors conclude that the weathering behavior
of Medieval glass is dictated primarily by chemical composition and that
ěreasonable agreementî exists between accelerated corrosion studies and
the analysis of archaeological specimens (p. 189).
In Chapter 6, ěThe Chemical Study of Metals - the
European Medieval and Later Brass Industryî (43 pp., 61 references), the
authors evaluate procedures for tracing metal objects back to their ore
source using trace element analysis. Precise chemical provenancing of metal
objects is not in general possible due to high temperatures and extreme
reduction conditions involved in processing the ores and finished metal.
Among the factors considered in trace element composition are the mineralogical
and chemical composition of the ore source(s), the thermodynamics and kinetics
of the processes used, and human factors such as the mixing and recycling
of metals. Disputed and conclusive archaeological occurrences of brass
artifacts and an historical overview of English and German brass and zinc
production - calamine (cementation) and direct mixing - are presented.
Most work on European Medieval specimens employs AAS and XRF. Case studies
concern the ěDrake Plate,î brass tokens, brass scientific instruments from
seven European countries, and British clocks. Three problems are related:
1) the need for the non-destructive analysis, 2) inhomogeneous copper alloys
especially in cast objects, and 3) de-zincification from the surface of
brass objects due to electrochemical process in water (and burial context)
which produces erroneous results.
Chapter 7, ěThe Chemistry and Use of Resinous Substancesî
(32 pp., 84 references), introduces major concepts in analytical organic
chemistry, focusses upon the higher plant resins and related substances
although excluding other plant exudates (latex and gum), and details plant
and animal organic molecules (see my review of Biers et al., Lost Scents
..., 1994, in SAS Bulletin 19(1-2): 4-6, 1996). Direct evidence is difficult
to obtain, but preservation is favorable in anaerobic environments because
of the protection from atmospheric and photoxidation, and the reduced growth
of microorganisms. The chemistry of resins and terpenes (mono- through
sesquiterpenoids) is reviewed. GC and GC-MS techniques are seen as valuable
for the separation and characterization of individual molecular species,
and complementary analytical data is derived from IR and NMR. The analytical
goal to identify precise species-specific botanical source(s) is problematical,
since heating introduces chemical changes. The case study focuses on birch
bark and tar used as a tool-fabricating adhesive by Ötzi, the Alpine
ěIceman.î There is considerable potential in the use of IR, TLC (Thin Layer
Chromatography), NMR, and GC-MS for the analysis of liquids (milk, mead,
beer, wine, etc.), plant and animal lipid residues, waxes, resins, waxes,
psychoactive substances, alkaloids, and caffeine. Important work by Noreen
Tuross at the Smithsonian Institutionís Conservation Analytical Laboratory
is not cited.
The subsequent Chapter, entitled ěAmino Acid Stereochemistry
and the First Americansî (31 pp., 52 references), concerns the racemization
of amino acids in bones and teeth. Recent studies by Dillehay (1997) supercede
some background materials on migration hypotheses and dating and accuracy.
Pollard and Heron consider the structure of bone, stereochemistry, AAR
(Amino Acid Racemization) of aspartic acid, and the AMS (Accelerator Mass
Spectrometry) 14C dating method which has superceded AAR. The case study
includes California Paleo-Indian specimens where initial AAR dates were
seriously overestimated versus AMS dates. The degree of organic preservation
in bone is a major factor, ědepending on the level of collagen surviving
in the bone, significantly different ages can be obtained on different
amino acid fractions from the same boneî - a variance of 2500-8000 years
(p. 290). Readers may wish to assess the statement that ě... the age limit
of 14C dating still remains at around 30-40,000 years BPî (p. 297). The
authors also consider briefly the forensic use of aspartic acid calibration
data on teeth to assist in predicting the age of humans at death.
In Chapter 9, ěLead Isotope Geochemistry and the
Trade in Metalsî (39 pp., 44 references), the authors state that lead isotope
analyses are ěfraught with problems far more than have been encountered
with the study of other archaeological materials, with the possible exception
of glassî (p. 302). Among these are defining isotopic signatures, and the
mixing and recycling of copper resources. The geochemical background to
the technique and TIMS (Thermal Ionization Mass Spectrometry) are detailed.
Three fundamental assumptions are reviewed: 1) anthropogenic processing
produces no isotropic fractionation, 2) the extent of a ělead isotope field,î
and 3) the interpretation of lead isotope data. Bronze Age Aegean and Cypriot
lead isotope analyses are reviewed in the case study, but specialists conclude
that it is impossible to subdivide eastern Mediterranean ore deposits into
separate fields to resolve questions of provenance.
Chapter 10, ěSummary Wither Archaeological
Chemistryî (6 pp., 8 references), includes an historical overview emphasizing
nondestructive techniques, considers the archaeological relevance of chemical
applications, and predicts the future of archaeological chemistry. The
authors state that the analysis of archaeological material has, in general,
been regarded as a specialist pursuit (p. 341). Computerization and the
need for smaller sample amounts have resulted in major, recent changes
in analytical capabilities. The authors also evaluate why, in some cases,
the traditional scientific applications of archaeometry have not delivered
answers to the questions which are of interest to mainstream archaeologists.
Analytical techniques, sampling restrictions, equipment expense, materials
conservation, preservation environments (soil/groundwater/object interactions),
and political and scientific agendas are considered. Lastly, they state
that ěthe real restrictions to archaeological chemistry are in terms of
ideas rather than practicalitiesî (p. 344).
Although not designed to cover comprehensively the
techniques of archaeological chemistry, this well written handbook/textbook
written, in the main, for chemists and archaeologists takes its place with
the significant writings of Brill, Kingery, Rice, Smith, and Tylecote in
any professional library emphasizing archaeological science. The contents
are current and accurate although the chapters vary in length and coverage
- some are more scientifically oriented (Chapter 7) while others are, in
the main, historical in scope (Chapter 6). The majority of the references
are to the British literature and there is a lack of citations to important
publications and chapters in the multi-volume series of the American Chemical
Societyís Archaeological Chemistry, five volumes to date, or the Materials
Research Societyís Materials Issues in Art and Archaeology, four volumes
to date (see Kolb 1996). The volume also addresses issues about the future
of archaeological science raised by Renfrew (1992) and Tite (1991). This
work is without question a tour de force and is recommended highly to students
and professionals in the physical sciences and archaeology.
References
Biers, William R., Klaus O. Gerhardt & Rebecca
A. Braniff. 1994. Lost Scents: Investigations of Corinthian ěPlasticî Vases
by Gas Chromatography-Mass Spectrometry. Philadelphia: University of Pennsylvania
Museum Center for Archaeology Research Paper 11.
Dillehay, Tom D. 1997. Monte Verde: A Late Pleistocene
Settlement in Chile, Volume 2: The Archaeological Context and Interpretation.
Washington: Smithsonian Institution Press, Smithsonian Series in Archaeological
Inquiry.
Goffer, Zvi. 1980. Archaeological Chemistry: A Sourcebook
on the Applications of Chemistry to Archaeology. New York: John Wiley.
Henderson, Julian (ed.). 1989. Scientific Analysis
in Archaeology. Oxford and Los Angeles: Oxford Committee for Archaeology,
Institute of Archaeology and UCLA Institute of Archaeology.
Jones, R.E. (ed.). 1986. Greek and Cypriot Pottery:
A Review of Scientific Studies. Athens: British School at Athens Occasional
Paper 1.
Kolb, Charles C. 1996. Ceramic Studies in Archaeology.
CHOICE: Current Reviews for Academic Libraries 34: 571-583.
Neff, Hector (ed.). 1992. Chemical Characterization
of Ceramic Pastes in Archaeology. Monographs in World Prehistory 7. Madison:
Prehistory Press.
Renfrew, A.C. 1992. The Identity and Future of Archaeological
Science. In A.M. Pollard (ed.), New Developments in Archaeological Science.
Proceedings of the British Academy 77: 285-293. Oxford: Oxford University
Press.
Tite, M.S. 1991. Archaeological Science - Past Achievements
and Future Prospects. Archaeometry 31: 139-151.