Chronometric method of dating ceramic materials by measuring the stored energy created when they were first fired. It is based on the principle that ceramic material, like other crystalline non-conducting solids, contains small amounts of radioactive impurities such as potassium, uranium, and thorium, which emit alpha and beta particles and gamma rays causing ionizing radiation. This produces electrons and other charge-carriers (holes) which become caught in traps in the crystal lattice. Heating of the pottery causes the electrons and holes to be released from the traps, and they recombine in the form of thermoluminescence. The amount of thermoluminescence from a heated sample is used to determine the number of trapped electrons resulting from the absorption of alpha radiation. The quantity of light emitted will depend on three factors - the number of flaws in the crystal, the strength of the radioactivity to which it has been exposed, and the duration of exposure. An age determination technique in which the amount of light energy released in a pottery sample during heating gives a measure of the time elapsed since the material was last heated to a critical temperature. The older a piece of pottery, the more light produced. Accuracy for the technique is generally claimed at ?10%. It overlaps with radiocarbon in the time period for which it is useful, spanning 50,000-300,000 years ago, but also has the potential for dating earlier periods. It has much in common with electron spin resonance (ESR).