Archaeology and Archaeological Chemistry in Israel

During a recent sabbatical year (1994–95), I had the good fortune to be appointed a Fulbright Lecturer for Israel, with major teaching responsibilities at the Shenkar College of Textile Technology in Ramat-Gan, The Hebrew University in Jerusalem, and the Weizmann Institute of Science in Rehovoth. Most of my work was carried out at the two Edelstein Centers, one for the History of Science, Technology and Medicine at the Hebrew University, and the other for the Analysis of Middle Eastern Artifacts and Related Objects at Shenkar College. The superb library holdings at the former provided the background for the research at the latter. In addition to my lecturing and textile research, I spent time at the Israel Antiquities Authority with Tamar Schick, who was engaged in examining the objects excavated from the "Cave of the Warrior", a major neolithic site in the Judean desert where an enormous burial shroud covered with red pigment, bowls, weapons, and other woven objects were uncovered. I also spent some time at the Israel Museum with Alisa Baginsky (Fig. 1) and Avigail Sheffer, textile conservators who in collaboration with Shenkar College published the definitive work on the textiles excavated from the Fortress of Masada. Masada, the supreme symbol of Israeli resistance and freedom, was the site of the Roman siege of the remnant of those who carried out the Jewish uprising in 70 CE. Numerous garments from that era were excavated from the site over the past several decades, and the textiles had to be characterized and the dyes on them analyzed (1, 2).

Figure 1. Alisa Baginsky displaying fragment of an ancient textile at the Israel Museum

Synthetic Medieval Blue Pigments in Italy

The second semester of my sabbatical took me to Italy, where I examined, transliterated, and translated medieval recipes for blue pigments found in manuscripts in a variety of Italian libraries: the Biblioteca Nazionale Centrale and the Biblioteca Casanatense, both in Rome; the Biblioteca Riccardiana and the Medicean Laurentian Library (Fig. 2), both in Florence; the library at Lucca in Tuscany; and the Monastery of San Lazzaro, in Venice. During a previous sabbatical year, I had engaged in a collaborative research project with New York University professors Norbert Baer and Manfred Low, which consisted of an examination of the blue pigments mentioned extensively in medieval artists' manuals found in other parts of Europe: Trinity College Library in Dublin, the Bodleian Library at Oxford, the British Museum in London, and the Bibliothèque Nationale in Paris. The recipes varied from some rather straightforward methods of making copper acetate to more mysterious "silver blue" recipes for which, as Cyril Stanley Smith has said, "the chemistry escapes us." The proliferation of these recipes is understandable in light of the fact that the only two blue pigments available to the medieval artist (between the eighth and the sixteenth centuries) were the very expensive azurite and ultramarine (3).

Figure 2. The courtyard of the Medicean Laurentian Library at Florence. This distinquished library, housed on the second floor (background), contains one of the largest collections of rare medieval Italian manuscripts on medical and artistic subjects.

Recipes for making artificial blue colors are very old. They are embedded in the literature of a technical tradition dating from the 3rd century CE that managed to survive five centuries of "dark ages" to reemerge in the late 8th or early 9th century in two Latin manuscripts, which contain recipes for making blue pigments from both copper and silver. In reproducing these early recipes, I tried to seek out materials that would be as close as possible to those available to the medieval artist or craftsman. My working thesis was that these compounds would be relatively common copper compounds readily identifiable by standard X-ray powder diffraction methods. It was therefore with great surprise that, after carrying out the instructions in several of the recipes, I found that the X-ray diffraction patterns of the products did not match anything in the powder diffraction file. It was necessary to perform single-crystal X-ray crystallography so that I could obtain the cell dimensions of one "silver blue" compound that turned out to be tetra-m-acetato-bisdiaquocopper(II) (4). Another elusive compound made from elemental copper, vinegar, and lime was identified as calcium acetate copper acetate hexahydrate, Ca(C₂H₃O₂)₂ · Cu(C₂H₃O₂)₂ · 6H₂O. This latter compound was the deepest, truest blue compound I made (Fig. 3), but its value as a pigment is doubtful because of its high solubility in water. The color also becomes considerably diminished when the compound is ground to a fine powder (5).

Figure 3. Results of a medieval pigment synthesis. The dark blue pigment is calcium acetate copper acetate hexahydrate.

Other blues with intriguing crystalline forms are still unidentified, including a beautiful blue with a morphology resembling rosettes (Fig. 4). Could it be that the medieval artist was such a good synthetic chemist that, to this day, we have failed to synthesize and characterize compounds produced many centuries ago? The mystery surrounding the blue pigments remains unsolved. Part of the problem is dealing with mixtures rather than with pure compounds; the blue crystals must be separated from the surrounding colorless matrix in order to be analyzed, and I have not yet been able to do this. In addition, I have some new and interesting recipes from my most recent foray into the Italian libraries that may cause the mystery to deepen.

Figure 4. An unidentified blue pigment (rosettes) made from a medieval recipe. These rosettes were produced by mixing "strong vinegar, lime, and sal ammoniac (ammonium chloride)" in a copper pot, then storing them under hot horse dung for fifteen days.

Another Function of Chemistry at the Interface: Deauthentication

An artifact or a work of art takes on greater value if it can be ascribed to a major artist or dated to an earlier age. Such potential value has attracted some very clever forgers who have sometimes managed to keep one step ahead of the scientific methods used to unmask them. Such methods can only be used to unmask, or "deauthenticate", an artifact; they can never be used to prove that an artifact is genuine. There are two general methods used to deauthenticate: content analysis and age-dating. The former relies on the fact that the content of an artifact must be consistent with the age from which it comes; the latter requires that the material of which an artifact is made must at least predate the age of the artifact itself. Two examples of the use of these methods follow.

The Archaic Mark

An ongoing project that I have been involved with deals with the application of small-particle analysis techniques to the study of pigments used in medieval manuscripts. One of these manuscripts, the Archaic Mark, Ms. 972 from the University of Chicago Special Collections, is a book of decidedly modest quality but of undeniable interest to philologists. An unpublished description of the manuscript notes that some readings find parallels in the early Codex Vaticanus, but that others are unique. One scholar was so dazzled by the textual evidence that he thought the Archaic Mark might contain the text of the Gospel of Mark in a more primitive form than any other known manuscript. On the other hand, others have suggested that its rare text may have been taken from a 19th century printed version of the Greek gospels, and some have even questioned the authenticity of the manuscript.

The problem of the Archaic Mark is quite complex. Its miniatures are based on the cycle in a late 12th-century gospel book in the National Library in Athens, codex 93. There exists also a set of fragmentary gospels in the Hermitage Museum in St. Petersburg that must have been made by the same scribe and illuminator because the similarities in script, initials, and painting style can hardly be fortuitous. Analysis of the ubiquitous blue pigment found in the Archaic Mark by FT-IR indicates that its identity is an iron, or Prussian, blue (Fig. 5). The iron blues are the first of the artificial pigments with a known history and an established date of first preparation. The color was made by the Berlin colormaker Diesbach in or around 1704. Moreover, the material is so complex in composition and method of manufacture that there is practically no possibility that it was synthesized independently in other times or places. This fact, in addition to the evidence indicating that both the Archaic Mark and the St. Petersburg gospel fragment were copies of the Athens codex 93, suggests that these manuscripts originated some time much later than their purported 12th-century fabrication. Furthermore, neither of these manuscripts has a genealogy that can be traced prior to about 1930, a fact suggesting that their origin may very well be during the flurry of Athenian forgeries that came to the market in the 1920s (6).

Figure 5. "The Soldiers Gaming for the Garments of Christ" from the Archaic Mark (Chicago Ms. 972). This purported 12th-century manuscript was found to contain large amounts of Prussian blue, an 18th-century pigment, thus throwing into doubt its date of origin. Used with permission of the Department of Special Collections, University of Chicago Library, Chicago, IL 60637.

The Shroud of Turin

The Shroud of Turin, a linen cloth alleged to be the burial shroud of Jesus Christ, has been unequivocally historically traced to mid-14th century possession by the House of Savoy in southern France. This 4.3 ¥ 1.1-m linen cloth bears straw-colored "negative" body images of a man who was crucified and scourged by a whip of Roman design. The body image (Fig. 6) is bracketed the entire length of the cloth by parallel burn and scorch marks from fire damage incurred in 1532. Waterstains from extinguishing this fire are also evident.

Figure 6. The Shroud of Turin: detail of the facial image. Aside from the question of the dating of the linen textile of the shroud, the origin of the image itself is controversial. Some scholars contend that the image was painted onto the shroud with iron(III) oxide; others believe that it originated from the decomposition of blood from the body that was enclosed therein. 1978 Vernon Miller. Used by permission.

In 1978 an international group of investigators, the Shroud of Turin Research Project (STURP), carried out several on-site investigations of the shroud and concluded that the image was not a painting, but rather that the body-image chromophore was an oxidation product of the cellulose of the linen fibers, and the blood images were blood-derived materials produced from contact of the cloth with a wounded human body. An independent investigation by Walter McCrone yielded the opposite conclusion: that the image on the shroud was a painting composed largely of iron(III) oxide with the addition of a considerable amount of cinnabar, HgS (7). Since it was clear that science could never authenticate the shroud as the burial cloth of Jesus, but could positively deauthenticate it, STURP strongly recommended and supported a radiocarbon dating test. Consequently, three laboratories independently radio-dated samples from the shroud by the accelerator mass spectroscopy (AMS) method and reported a reasonably precise 14th century date, in apparent agreement with the known historic record (8). Unfortunately, the recommended detailed sampling protocol that would assure both precision and accuracy was not followed. Subsequent FT-IR and scanning electron microprobe data showed that the samples taken for radiocarbon dating were not representative of the bulk of the nonimage portions of the Shroud (9) These inherent uncertainties in the radiocarbon date led a group of Russian scientists to question the accepted radiocarbon date. Working on the hypothesis that conditions comparable to those suffered by the shroud in the 1532 fire at Chambéry can produce a large error in radio-dating due to large kinetic isotope effects, this group devised a laboratory model to simulate the fire conditions of 1532. Their results showed that radiocarbon dates of experimental textile samples incubated under fire-simulating conditions are subject to significant error due to incorporation of significant amounts of 14C and 13C atoms from external (modern) combustion gases into the textile cellulose structure. Taking this fire-induced carboxylation of the textile fibers into consideration, the Russian group concluded that their correctional calculations modified the conventional radiocarbon date of the shroud to the 1st or 2nd century CE (10).

Conclusion

Chemistry at the interface of history, art and archaeology is an interesting meld of disciplines that can help to solve old questions about archaeological artifacts and works of art. Within this context, the task of the archaeological chemist has become more complex than ever. Once the domain of analytical chemists turned "amateur archaeologists", effective work in this area demands increasingly sophisticated equipment by way of advanced instrumentation, increased knowledge of statistical software packages, increased interaction with members of related disciplines, and awareness of the ever-burgeoning literature of archaeometry, archaeology and anthropology. Chemists working in this area must be aware of the fact that analytical data can be completely meaningless unless they are interpreted within the matrix surrounding the artifact or sample being investigated.

Related Laboratory and Classroom Material

While the examples contained in this paper are not exhaustive of the innovative work taking place at this moment at the multidisciplinary interfaces of this effort, they are a representative sample of such work and provide an overview for the interested chemical educator. In addition, the bibliography for each of the areas discussed herein provides the reader with further material for study.

For those interested in pursuing the investigation of pigments in student laboratory activities, the ChemSource materials include an activity on synthesis of Prussian blue and making gouache paint (11). There is also an article on art, archaeology, and analytical chemistry in this Journal (12). Both of these appear in their entirety as supplements to this article (refer to Supplements link on this page).

Acknowledgments

Working at the interface of art and archaeology has afforded the added joy of being able to involve all of my students at every phase of my work. Chemistry majors have worked side by side with art majors in carrying out research plans and interpreting data, and much of what I report here has been the work of undergraduate students on both sides of the Atlantic. Many of my students have presented papers at national ACS meetings, and this is the aspect of the work of which I am particularly proud. No award is achieved in a vacuumit is the result of cooperative and supportive effort on the part of many. I am deeply grateful to my colleagues, friends, and especially to my students, for the interest and joy of learning that kept me going.

This paper was adapted from "Doing Chemistry at the Art/Archaeology Interface" (13).

Literature Cited

1. Sheffer, A.; Granger-Taylor, H. Masada IV: The Yigal Yadin Excavations 1963­1965; Final Reports; Israel Exploration Society, The Hebrew University of Jerusalem: Jerusalem, 1994; pp 149-282.

2. Koren, Z. C. In Archaeological Chemistry: Organic, Inorganic and Biochemical Analysis; Orna, M. V., Ed.; ACS Symposium Series 625; American Chemical Society: Washington, DC, 1996; pp 269-310.

3. Orna, M. V.; Low, M. J. D.; Baer, N. S. Stud. Conserv. 1980, 25, 53-63.

4. Orna, M. V.; Low, M. J. D.; Julian, M. M. Stud. Conserv. 1985, 30, 155-160.

5. Orna, M. V. In Archaeological Chemistry: Organic, Inorganic and Biochemical Analysis; Orna, M. V., Ed.; ACS Symposium Series 625; American Chemical Society: Washington, DC, 1996; pp 107-115.

6. Orna, M. V.; Lang, P. L.; Katon, J. E.; Mathews, T. F.; Nelson, R. S. In Archaeological Chemistry ­ IV; Allen, R. O., Ed.; American Chemical Society: Washington, DC, 1989; pp 196-210.

7. McCrone, W. Accounts Chem. Res. 1990, 23, 77-83.

8. Damon, P.; et al. Nature 1989, 337, 611-615.

9. Adler, A. D. In Archaeological Chemistry: Organic, Inorganic and Biochemical Analysis; Orna, M. V., Ed.; ACS Symposium Series 625; American Chemical Society: Washington, DC, 1996; pp 223-228.

10. Kouznetsov, D. A.; Ivanov, A. A.; Veletsky, P. R. In Archaeological Chemistry: Organic, Inorganic and Biochemical Analysis, Orna, M. V., Ed.; ACS Symposium Series 625; American Chemical Society: Washington, DC, 1996; pp 229-247.

11. "Synthesis of Prussian Blue and Making a Gouache Paint"; In Sourcebook V. 3.0, a Component of ChemSource, Vol. I; Orna, M. V. et al., Eds.; American Chemical Society: Washington, DC, 1997 (in preparation).

12. Beilby, A. L. J. Chem. Educ. 1992, 69, 437-439.

13. Orna, M. V. The Nucleus (Northeastern Section, American Chemical Society) 1996, LXXV(4), 9­13. Used with permission.

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