Volume 43 | Number 1 | Fall 2012

Striking Gold

Fall 2012 Issue

Using a powerful scanning electron microscope at the Idaho State University Center for Archaeology, Materials, and Applied Spectroscopy (CAMAS), ISU anthropologist and research scientist David Peterson is helping shed light on the making of gold by nomadic horsemen nearly 4,000 years ago on the Eurasian steppe grasslands of present-day Russia.

About 1850-1700 B.C., at the beginning of the Late Bronze Age in Russia's Middle Volga River Region, herders began to settle in small villages and buried their dead in burial mounds known as kurgans.

Peterson discovered that ornaments from these graves were decorated using a technique called depletion gilding. Late Bronze Age inhabitants of the Middle Volga covered pendants with a foil no more than one-tenth of a millimeter thick made of an alloy of gold and silver known as electrum. While the overall gold content of the foil is less than that of the silver, through depletion gilding ancient Eurasian metallurgists were able to manipulate the concentration of gold on the outer surface to make the ornaments look like solid gold.

What is even more remarkable is the incredibly small amount of gold they needed to do this, Peterson said. Through the application of heat and naturally occurring chemicals, silver was depleted from the outer five micrometers of the foil covering one pendant, which made it appear as though it was made of pure gold (a micrometer is one thousandth of a millimeter). The gold-enriched surface is so microscopically thin that its thickness could only be measured by looking at a section cut through it with a scanning electron microscope.

"Finding the use of this technique in the Russian steppes is fascinating because it's an example of the use of a remarkable technology simply for ornamentation, more than a thousand years before gilding techniques were perfected in ancient Greece and Rome," Peterson said.

Prior to Peterson's findings, this gilding method had only been identified and published in one other instance in the Old World, hundreds of miles to the south in Mesopotamia. Although discovered first in artifacts from the Andes, this gilding method was used much earlier in Mesopotamia and the Eurasian steppes.

Peterson began research in this area of Russia with colleagues at the Institute of History and Archaeology of the Volga in Samara, Russia at Hartwick College in Oneonta, N.Y., while he was a graduate student. He received minute samples of the kurgan gold from his Russian colleagues Pavel Kuznetsov and Oleg Mochalov, who allowed him to remove small sections from three foil-covered pendants.

After examining the samples at the ISU Center for Archaeology, Materials, and Applied Spectroscopy, Peterson concluded that corrosion-based depletion gilding was applied to the foil on one of the pendants, and that a depletion gilding process may have been used on the other two, which are from a burial in a different Srubnaya kurgan cemetery at Nizhnyaya Orlyanka in Russia.

ISU Photographic Services/Susan Duncan