SAS Bulletin

Volume 20   Number 1/2   January /June 1997

Archaeological Chemistry.

A. Mark Pollard & Carl Heron. The Royal Society of Chemistry, RSC Paperbacks, Cambridge, UK, 1996. xv + 375 pp. £ 22.50, $46.00 (paper). ISBN 0-85404-523-6.

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.

    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.

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