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Analytical Chemistry

Dating Artifacts Nondestructively

ACS Meeting News: Plasmas and supercritical fluids could replace harsh acid and base soaks for cleaning archaeological relics

by Jyllian Kemsley
March 29, 2010 | APPEARED IN VOLUME 88, ISSUE 13

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Credit: Marvin Rowe/Texas A&M
A piece of 1,500-year-old Egyptian fabric shows no significant difference before (left) and after plasma treatment.
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Credit: Marvin Rowe/Texas A&M
A piece of 1,500-year-old Egyptian fabric shows no significant difference before (left) and after plasma treatment.

A new technique involving plasmas and supercritical fluids allows archaeologists to determine the age of artifacts without damaging them, reported Marvin W. Rowe, a chemistry professor at Texas A&M University, on Tuesday at the ACS national meeting in San Francisco.

Traditional radiocarbon dating techniques typically require removing a sample from an artifact. The sample is then cleaned by soaking it in strong acid, base, and acid again at 50 °C to rid it of contaminating organic material. Finally, it is burned before using accelerator mass spectrometry to look for 14C.

Rowe, in collaboration with University of Central Arkansas chemistry professor Karen L. Steelman, previously developed a technique to use oxygen plasma to oxidize carbon in artifacts to CO2 and then collect the gas and convert it to graphite for radiocarbon analysis (Am. Antiquity 2004, 69, 741). Now, they've extended the method to eliminate the harsh cleaning steps, instead using argon and oxygen plasmas to replace the acid soaks and a supercritical fluid composed of CO2 and methanol to replace the base.

The whole approach yields accurate dates with little visible change in material as fragile as 5,000-year-old eggshells and 2,000-year-old cloth and grass, Rowe said. Whole artifacts can also be analyzed intact, limited only by the size of the reaction chamber, he added.

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