Fire and water reveal true age of ancient relics

Fire and water are all that is needed to unlock the internal clocks' of archaeological remains and accurately reveal their age, say scientists. The research, published online today in Proceedings of the Royal Society A, will help archaeologists date remains that are thousands of years old, and also reveal where other techniques go wrong.

Dating methods are of paramount importance in the earth and environmental sciences, palaeontology, archaeology, and art history. Fired clay material such as bricks, tile and ceramics represent an important sample of the remains unearthed at archaeological digs, but they are notoriously hard to date accurately. Carbon 14 dating, which can be used on bone, does not work with ceramics, and those techniques that do exist are extremely complex.

Now a team of scientists from the Universities of Manchester and Edinburgh have found a surprisingly simple way to get around this issue.

From the moment they are fired, ceramics begin to absorb moisture from the environment which causes them to gain mass. Using a technique they call rehydroxilation dating' researchers led by Dr Moira Wilson from the University of Manchester found that heating a sample of the relic to extreme temperatures causes this process to be reversed all the moisture it has gained since it was fired is lost again.

The more weight a sample loses during heating, the more moisture there was to start with, and so the older the relic. After heating, Wilson and her team used an extremely accurate measuring device to monitor the sample as it began to recombine with moisture in the atmosphere. They then used a law to predict how long it would take for all the water lost in heating to be reabsorbed, and so reveal the true age of the sample.

To test their new technique the scientists teamed up with the Museum of London and tried it out on samples of know age. They successfully dated brick samples from the Roman, medieval and modern periods, and the method was so accurate that it looks to become the way in which such artefacts are dated in the future, according to Wilson.

So far, the technique has been used with specimens that are as much as 2000 years old, but has the potential to be used on much older artefacts, says Wilson, even those dating back 10,000 years.

What's more, the technique has revealed a flaw in previous dating verdicts. When clay objects are submitted to extreme temperatures, and moisture removed, this internal clock' is reset. That means that objects that have been subjected to extreme heat, such as those dating back to the WWII Blitz are often, in truth, much older.

The technique has far reaching implications. 'As well as the new dating method, there are also more wide-ranging applications of the work, such as the detection of forged ceramic,' says Wilson. 'The method could also be turned on its head and used to establish the mean temperature of a material over its lifetime, if a precise date of firing were known,' she adds, which could make the method a useful tool for climate change studies.