Thermoluminescence dating simple definition
The TL laboratory at Daybreak was established in 1977 to make TL available to the art community in general. Studies at Oxford back in the 70s on Romano-British pottery indicated that when all quantities entering the age equation are measured, the TL date of a single potsherd will typically fall within 15 per cent of the known date.
Most mineral materials, including the constituents of pottery, have the property of thermoluminescence (TL), where part of the energy from radioactive decay in and around the mineral is stored (in the form of trapped electrons) and later released as light upon strong heating (as the electrons are detrapped and combine with lattice ions).Luminescence is emission of light by a substance not resulting from heat; it is thus a form of cold-body radiation.It can be caused by chemical reactions, electrical energy, subatomic motions or stress on a crystal, which all are ultimately caused by Spontaneous emission.Much stoneware is not so hard as porcelain and may be sampled by drilling.The clay cores from lost wax metal castings may readily be tested.This is adequate for the purposes of authentication where the question is whether the piece was fired in antiquity or recently; it will not differentiate, say, between a classic Greek terra cotta and a Roman copy.
In some categories of objects, from China, for example, the actual age is quite precisely known for short-lived styles, and it is possible to work "backwards" to get information about the environment in many parts of the world, and some other parameters not usually measurable for art objects.
Drilling, the usual method of sampling, introduces some uncertainty.
It is also rare that any information about the radiation from the burial soil can be obtained, as art objects are usually thoroughly cleaned.
A leaflet from Daybreak describing the TL technique in more detail and giving a bibliography will be provided to interested persons.
The phenomenon of thermoluminescence was first described by the English chemist Robert Boyle in 1663.
It was employed in the 1950's as a method for radiation dose measurement, and soon was proposed for archaeological dating.