ANCIENT GLYPTIC ART – GEM ENGRAVING and GEM CARVING

GEM ARCHAEOLOGY

lyptic art, the craft of gem carving, dates at least to the the 7th millennium B.C., developing into a highly sophisticated industry in the Indus Valley Civilization from the mid-fourth to late second millennium B.C. As in other civilized societies, whether ancient or modern, gems engraved as sealstones and personal signets were not only ornamental adornments, but also were objects of indispensible utility, which, impressed into wax or clay, represented a legal signature, or personal identification, not unlike a driver's license or ID card today, or notarial imprimatur on business and bureaucratic transactions. The "device" or engraved part of a gem customarily was cut to read backwards in the stone, so that the engraving, such as a signature or right-facing portrait, would read right in the impression. An especially pretty or interesting-looking stone might be reserved for carving by only the best carver or only for the most important patrons. Pyrgoteles, for example, was the only gem cutter authorized to engrave the likeness of Alexander the Great in the rare gemstone, smaragdos (a green-colored stone from which the term for the modern beryl variety "emerald" is derived).

Art historians, archaeologists and connoisseurs have examined ancient texts—anonymously carved Mesopotamian inscriptions, Theophrastus's On Stones, Pliny the Elder's Natural History—as well as archaeological literature to inform our current understanding of the importance of gems and glyptic art in antiquity. From these texts scholars have inferred the gem varieties that were known in antiquity, their origins, and enhancement techniques that may have been applied to them intentionally by the ancient lapidary to improve or otherwise alter their appearance. The iconography or subject matter depicted in engraved gems, or intaglios, has been the primary focus of study.

Gemological and analytical study has been limited. Instead, the material attributes published on ancient gems have been reported anecdotally in successive journals, papers, and books, repeating for centuries erroneous interpretations of corrupt texts or observations based on sight alone, without the benefit of analytical verification.

Peri Lithon, or On Stones, written in the fourth century B.C. by Theophrastus, is the most important text about gems of the Classical world. It is the earliest scientific treatise on any subject extant in western literature, and is the antecedent of our modern scientific system of classification. Although it survives only as a fragmentary book, On Stones presents a taxonomy of the gems known in ancient times, describing their origins, physical properties, and magical or other special attributes. Gemological study offers an illuminating perspective on the ancient literature and a re-assessment of archaeological literature, enabling correction of some inaccurate information and clearer rendering of opaque passages, particularly concerning gemstone origins and the nature of accidental alterations effected through burial, for example, or treatments applied intentionally to gems by the ancient lapidary.

Various analytical techniques are used in gemstone identification, when standard gemological techniques prove inconclusive. A technique that has been employed for many decades is powder X-Ray Diffraction (powder XRD) analysis. Identification of an unknown sample is accomplished by comparing its crystalline structure against a reference base of known minerals.

Raman spectroscopy is being used increasingly to identify gemstones, employing a reference base of known gem spectra for comparison with unknown samples. Both qualitative techniques, such as X-Ray Fluorescence spectroscopy, and quantitative techniques, such as electron microprobe analysis, are useful in treatment detection and provenance studies, respectively.

ARCHAEOMETRY | GEM PROVENANCE STUDIES | GEMSTONE ORIGINS

any gems and their sources are described in ancient texts, notably Peri Lithon, by Theophrastus. The Periplus Maris Erythraei is a seafarer's first-hand chronicle describing the routes of trade, ports of call, and goods acquired during a merchant ship's long journey originating at a Red Sea port, venturing down the east coast of Africa and across the open sea to India's Malabar Coast and, finally, home again. The Periplus probably was written sometime between the first century B.C. and the first century A.D. Although fragmentary, it is one of the most important ancient texts that offers first-hand insight into the scope of trade and sea travel in the late Classical world. The brief account includes gemstones in the inventory of exotic goods acquired.

Ancient and archaeological references do no offer sufficient details to infer with certainty the identity of all the gems known in ancient times or their specific sources. In fact, very few of the gem localities that were exploited in antiquity are known today with certainty. Sometimes, however, the gemstones themselves can offer clues about their origins. Some gems, such as garnets, have a distinctive chemical composition and crystalline structure that make possible associating them with their sources. Other gems contain characteristic internal features, or inclusions, that tend to link them with a high degree of probability to a particular gem-producing region. The characteristic angular three-phase inclusions often observed in Colombian emeralds, are a well-documented example.

GEMSTONE ENHANCEMENT | TREATMENT RECIPES APPLIED IN ANTIQUITY

he treatment or enhancement of gemstones and treatment detection is an important topic in gemology today, but it has been largely overlooked in relation to gems of the ancient world. Although gemstone treatments in antiquity do not rival the sophistication of some of the techniques employed to enhance gems today, detection of them is no less challenging. Archaeological and ancient literature describe treatment techniques that ancient lapidaries employed to produce imitations or to improve the appearance of natural gemstones; however, empirical evidence that corroborates the textual references have been examined infrequently.

Some gem enhancement techniques used today, such as heating, sugar-treatment, quench-crackling, and dyeing, have been passed down over many centuries, the techniques changing little since antiquity. The pyrotechnology developed to deepen the color or intensify the banded patterns of quartzes is quite old, and is one of the most sophisticated and earliest technological achievements of the Indus Valley civilization, dating to the seventh millennium B.C. Controlled heating, for example, is a simple technique that changes purple amethysts into pale grayish green prasiolites or, with further heating, into yellow citrines, which are quite rare in nature.

SELECTED READING—ARCHAEOLOGICAL REFERENCES

J. Boardman, The Greeks Overseas: Their Early Colonies and Trade. Rev. edn. (London: Thames & Hudson, 1999)

L. Casson, Travel in the Ancient World. 1974 New edn. (Baltimore: Johns Hopkins Univ. Press, 1994)

——, Ancient Trade and Society. (Detroit: Wayne State Univ. Press, 1984)

D. Collon, First Impressions: Cylinder Seals in the Ancient Near East. (London: British Museum Publications, 1987)

A. Furtwängler, Die antiken Gemmen. 3 vols. Reprint of the 1900 edn. (Amsterdam: A. Hakkert, 1964-1965)

R. J. Forbes, Studies in Ancient Technology. Vols. 1, 3, 7. (Leiden: Brill, 1964, 1965, 1966)

J. M. Kenoyer, Ancient Cities of the Indus Valley Civilization. (Karachi: Oxford Univ. Press, 1998)

Periplus Maris Erythraei. Trans. Lionel Casson. The Periplus Maris Erythraei (Princeton: Princeton Univ. Press, 1989)

P. R. S. Moorey, Ancient Mesopotamian Materials and Industries, The Archaeological Evidence. (Oxford: Clarendon, 1994)

A. L. Oppenheim, "Mesopotamia in the Early History of Alchemy," Revue d'Assyriologie 60.1. (1966: 29-45)

Pliny the Elder, Natural History. Loeb Classical Library, trans. D. E. Eichholz. (Cambridge: Harvard Univ. Press, 1989)

Theophrastus, On Stones. Trans. Earle R. Caley, and J. F. C. Richards. On Stones. Introduction, Greek Text, English Translation, and Commentary. (Columbus: Ohio State Univ., 1956)

SELECTED READING—GEMOLOGICAL and ANALYTICAL REFERENCES

K. Nassau, "Miscellaneous Gemstone Treatments-Parts 1-3." Lapidary Journal 39.2-4 (1985: 254-62/30-40/16-23)

——, Gemstone Enhancement. London: Butterworths, 1984)

——, "The Early History of Gemstone Treatments," Gems & Gemology 20.1 (1984: 22-33)

J. Ogden, Jewellery of the Ancient World. (London: Trefoil, 1982)

E. J. Gübelin and JI Koivula, Photoatlas of Inclusions in Gemstones, volume 2. (Basel: Opinio Verlag, 2006)

——, Photoatlas of Inclusions in Gemstones, volume 1, 4th edn. (Basel: Opinio Verlag, 2004)

P. C. Keller, Gemstones of East Africa. (Phoenix: Geoscience Press, 1992)

——, Gemstones and Their Origins. (New York: Van Nostrand Reinhold, 1990)

R. T. Liddicoat, Handbook of Gem Identification. 12th edn. (Los Angeles: The Gemological Institute of America, 1993)

M. Sax, with C. Cavey, A. Jobbins, and G. Seidmann, "Recognition and Nomenclature of Quartz Materials with Specific Reference to Engraved Gemstones." Jewellery Studies 7 (1996: 63-72)

. Summers, Ancient Mining in Rhodesia and Adjacent Areas. Museum Memoir No. 3. (Salisbury: Trustees of the National Museums of Rhodesia, 1969)

L. Thoresen, ed., On Gemstones: Gemological and Analytical Studies of Ancient Intaglios and Cameos. Forthcoming.

O. Untracht, Jewelry Concepts and Technology. (Garden City: Doubleday, 1982)

R. Webster, Rev. P. G. Read, Gems: Their Sources, Descriptions and Identification. 5th edn. (Boston: Butterworth-Heinemann, 1994)

Chromium-bearing chalcedony is a rare gem material of vivid, emerald-green color. Its earliest use appears to have occurred around the first century BC/AD. Through the second century AD this gem material circulated widely throughout the Roman Empire. Gem cutters favored using this material for ringstones worn by women and children, with bucolic scenes among the favorite subjects depicted. Sometime in the second century A.D., or slightly later, chrome chalcedony disappeared from use and was not "discovered" again until 1955 in Zimbabwe. A small number of other sources of chromium-bearing chalcedony have been reported since the mid-1980's. The first century AD Roman intaglios shown here with their impressions are from the Michael Shubin Collection. Photograph by Lisbet Thoresen.

Three-phase inclusions, like the one shown here, are characteristic of Colombian emeralds. A halite crystal and an amorphously-shaped droplet of liquid is trapped inside an irregularly-shaped negative crystal. Photomicrograph by John I. Koivula.

"Zebra stripes" or "soap scum" pattern in an inclusion, like the one shown here, is caused by polysynthetic twinning, a phenomenon that is diagnostic for amethyst and no other gem variety. The "zebra stripe" inclusion in this gem, the yellow variety of crystalline quartz known as citrine, proves that it is not a natural citrine, but attained its color through heat-treatment of amethyst. The intaglio in which this inclusion was observed dates either to the first century AD or is a post-Classical copy after an ancient intaglio. FG 2350, Antikensammlung, Staatliche Museen zu Berlin. Photomicrograph by Lisbet Thoresen.

The large chip in this profile view of an ancient sealstone carved from agate is clear evidence that the seal's dark-colored bands were produced through treatment. Sugar-treatment is one of the oldest treatment techniques employed by lapidaries to deepen the color and contrast in agates, onyx and sardonyx. From the Michael Shubin Collection. Photograph by Lisbet Thoresen.