Measuring the intensity of the luminescence can determine how much time has passed since the last time the object was heated.
The light is proportional to the amount of radiation absorbed since the material was last heated.
This usually occurs when the items are heated to 350 degrees Celsius.
Therefore, in archaeology, thermoluminescence dating works best for ceramics, cooking hearths, incidentally fire-cracked rocks, and deliberately fire-treated rocks, such as flint or chert.
When collecting samples for thermoluminescence dating, several samples from different vessels should be taken, not smaller than 1 gram.
Samples should not be exposed to heat and powdery examples should not be exposed to bright light.
When the sample is heated in the lab, it releases thermoluminescence light.
The intensity of the thermoluminescence light is proportional to the time that has passed from the last clock resetting event, which for ceramics correspond to when it was baked.
Natural radioactivity causes latent thermoluminescence to build up so the older an object is, the more light is produced.
Therefore, thermoluminescence dating is actually determining the last time a crystal was heated and electrons were released.
Thermoluminescence dating is generally not very accurate.
The accuracy of thermoluminescence dating is only about 15% for a single sample and 7 to 10% for a suite of samples in a single context.
Unfortunately there are no affordable direct methods for dating pigments, except in some cases as we will see later.