Researchers at the University of Bristol have developed a new method of dating pottery -- that was used to cook.
The approach involves carbon-dating animal fat residue recovered from the pores in such vessels, the team explains. Previously, archeologists would date pottery either by using context information -- such as depictions on coins or in art -- or by dating organic material that was buried with them. This new method is much more accurate, however, and the team explains it can be used to date a site even to within a human life span.
Being able to directly date archaeological pots is one of the "Holy Grails" of archaeology," says Professor Richard Evershed from the University of Bristol's School of Chemistry, who lead the research.
"This new method is based on an idea I had going back more than 20 years. We made several earlier attempts to get the method right, but it wasn't until we established our own radiocarbon facility in Bristol that we cracked it."
Really old pottery, for example those made and used by stone-age farmers, is pretty tricky to date. Some are pretty simple and not particularly distinctive, and there is no context to date it against. So archeologists use radiocarbon dating, or 14C-dating, to analyze bones or other organic material that was buried with the pots. This is an inexact measurement and less accurate than dating the pots directly. Raw clay or fired pots, however, can't be dated this way.
Professor Evershed's idea was to analyze fatty acids from food preparation -- which can be dated -- that were protected from the passage of time within the pores of these pots. The team used spectroscopy and mass spectrometry to isolate these fatty acids and check that they could be tested.
As an experimental proof of concept, they analyzed fat extracts from ancient pottery at a range of sites in Britain, Europe, and Africa with already precise dating which were up to 8,000 years old, with very good results.
"It is very difficult to overstate the importance of this advance to the archaeological community," says Professor Alex Bayliss, Head of Scientific Dating at Historic England, who undertook the statistical analyses. "Pottery typology is the most widely used dating technique in the discipline, and so the opportunity to place different kinds of pottery in calendar time much more securely will be of great practical significance."
The new method has been used to date a collection of pottery found in Shoreditch, thought to be the most significant group of Early Neolithic pottery ever found in London. It is comprised of 436 fragments from at least 24 separate vessels and was discovered by archaeologists from MOLA (Museum of London Archaeology). Analysis of traces of milk fats extracted from these fragments showed that the pottery was 5,500 years old. The team were able to date the pottery collection to a window of just 138 years, to around 3600BC.
These people were likely linked to the migrant groups who first introduced farming to Britain from Continental Europe around 4000 BC, the team explains.
The paper "Accurate compound-specific 14C dating of archaeological pottery vessels" has been published in the journal Nature.