Scientists have found a way of dating archaeological ceramics - by defining how they react with moisture from the air.
The simple method promises to be as important for dating ceramic materials as carbon dating has become for organic materials such as bone or wood.
A team from the Universities of Manchester and Edinburgh has discovered the technique, which can be used on fired clay ceramics such as bricks, tiles and pottery.
Working with the Museum of London, the team has dated brick samples from Roman, medieval and modern periods with remarkable accuracy.
Their technique has been used to determine the age of objects up to 2,000 years old - and the team is confident that it will date ceramics 10,000 years old and more.
Researchers plan to look at whether it can be applied to earthenware, china and porcelain.
The method relies on the fact that fired clay ceramic material begins to react with atmospheric moisture as soon as it is removed from the kiln after firing.
This continues over its lifetime, causing the object to increase in weight. Researchers discovered a law that defines how this weight gain changes over time.
To determine the age of a ceramic object, a sample is weighed and then heated to around 500 degrees Celsius.
This removes the combined water from the sample, which is then weighed again. After that, the sample is exposed to moist air and the rate of mass gain accurately measured over a few days.
Using the law, it is possible from the weight gain to calculate the time needed for the object to regain the original weight - revealing its age.
The study, funded by the Leverhulme Trust and the Engineering and Physical Science Research Council (EPSRC), was published in the Proceedings of the Royal Society A.
This technique will allow us to discover a great deal about ancient artefacts by pinpointing their age. Our work is also scientifically important in showing that these everyday ceramic materials undergo long-term alteration over thousands of years, which can be described by a precise mathematical law.