| 1 October 2003
New method for dating pottery
Researchers at the University of Bristol (England) have developed the first direct method of dating ancient pottery, through analysis of animal fats preserved inside the ceramic walls. The new technique will allow more accurate determination of the age of pottery and, by extension, the age of associated artefacts and sites.
Although chemical analysis has, in the past, been used on residues found on the surface of pottery and shards, contact with the soil was always likely to produce corrupt data. Now research carried out by Richard Evershed, Ph.D and colleagues from the University has discovered that lipids (animal fats) are preserved through absorption into the material, in large enough quantities to allow radiocarbon dating. “Lipids are absorbed because most interesting pottery of any respectable age is unglazed,” says Evershed. “We’re taking a piece of pot and grinding it to a powder, and then extracting lipid that’s penetrated right down into the fabric.” A technique called capillary gas chromatography isolates the lipids. Purified compounds are then radiocarbon dated using an accelerator mass spectrometer at the Oxford University Radiocarbon Accelerator Unit.
Pottery is essential for dating archaeological sites. Although organic material can be dated by radiocarbon techniques, the results are not always reliable. Wood, for instance, can decompose over time; and animals often move bones around a site. Ceramics, on the other hand, have a long and stable lifespan. Later pottery can be easily dated by typology, but earlier ceramic material can be much harder because of its crude appearance. In the earlier research that led to the development of the new technique, Evershed’s team found the first direct evidence that people were dairy farming in Britain as long as 6,000 years ago. The prominence of fats in material from Neolithic, Bronze and Iron Age sites is consistent with their wide range of uses in the ancient world: lubricants, waterproofing agents, cosmetics, ointments, perfumes, varnishes, etc.
The researchers have now analyzed 15 pieces of pottery ranging in age from 4000 BCE to the 15th Century CE. These were blind-dated using the new method and then compared with verified dates. In all cases there was good correspondence of blind and validated dates. Evershed and his colleagues now plan to study mummies. “A lot of mummies were exported out of Egypt by the Victorians, and they often applied modern treatments to preserve them.” The researchers hope to distinguish between modern treatment and the original embalming agent.
According to Evershed, his method could be used to date any material that has preserved organic compounds. “You could even isolate individual amino acids by this preparative GC approach, but no one’s tried that. That’s the next step.” Evershed’s findings were featured ‘Analytical Chemistry’, the journal of the American Chemical Society.
Source: American Chemical Society (29 September 2003)
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