Scientists at the University of Manchester announced last week a breakthrough in the dating of ceramic (pottery) objects. Called rehydroxylation dating, “the method relies on the fact that fired clay ceramic material will start to chemically react with atmospheric moisture as soon as it is removed from the kiln after firing. This continues over its lifetime causing it to increase in weight – the older the material, the greater the weight gain.” Initial tests on materials up to 2,000 years old have been accurate within a decade. If this method proves reliable in dating earlier objects, it could be quite useful in solving, for instance, the current debate over 10th-9th century BC pottery in Israel. One problem with this method for archaeological sites is that the “internal clock” of the pottery is “reset” if the temperature reaches 500 degrees Celsius. Thus the pottery from areas destroyed by fire would only date to the year of the destruction and not to the date of creation.
The results of the report are covered in a popular article by Science Daily, or you can read the original article (pdf) in the Proceedings of the Royal Society A (alternate link here). The paper’s abstract:
The majority of ceramics are found in archaeological deposits and are extremely difficult to date. The typical method of using radiocarbon dating used for bone or wood cannot be used for ceramic material because it does not contain carbon, and luminescence dating is far too complex. Scientists from the Universities of Edinburgh and Manchester have discovered a new method of ceramic dating which is published in Proceedings of the Royal Society A..
Their new ‘rehydroxylation dating’ method stems utilises the fact that fired clay ceramics start to react chemically with atmospheric moisture as soon as it is removed from the kiln. The ultra-slow recombination of moisture appears to be generic in fired-clay ceramics and obeys a precise power law, which acts as an ‘internal clock’. Rehydroxylation dating enables scientists to date brick samples from Roman, medieval and modern periods.