Appendix: the Thermoluminescence Tests

Extract

Thermoluminescence (TL) applied to the dating and authenticity testing of ancient ceramics is a well established technique.

Thermoluminescence is the light given out by non-conducting crystalline materials as a result of exposure to radiation and subsequent heating. In pottery the crystalline inclusions, such as quartz and feldspars, are responsible for the TL. The radiation results from minute quantities of radioactive impurities in the pottery itself and in its immediate environment. The TL signal measured in the laboratory is related to the time elapsed since either the formation of the crystalline inclusions or since they were last fired to a temperature of about 500°C or above. The dating of pottery by TL is therefore only possible due to the removal during firing by man of the effect of previous radiation over geological time. The TL signal is then proportional to the age of the pottery. When a ceramic is fired to a temperature which is not sufficient to remove the effect of previous radiation, the TL signal is normally in saturation, i.e. addition of a laboratory radiation dose prior to heating does not enhance the TL signal. In such cases, TL cannot be used to determine the authenticity or otherwise of the object.