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.
Then we need to correlate thermoluminescence light to radiation dose rate per year which the sample has received since its last clock resetting event.
Eventually, we will follow this formula to found out how many years old the sample is: Age (year) = accumulated dose / dose rate per year Thermoluminescence dating can be performed only in a specialized laboratory which will have a chemical section for the treatment of the samples with reagents and a radiation hazard restricted area.
Energy absorbed from ionizing radiation frees electrons to move through the crystal lattice, some of which are trapped at imperfections in the crystal lattice.
Later, heating releases the trapped electrons, producing light.
Samples should be placed in a polyethylene bag and sealed with electrical tape.
To test the date we need to measure the sample’s thermoluminescence light which is then correlated to the accumulated dose of ionizing radiation.
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.
Unfortunately there are no affordable direct methods for dating pigments, except in some cases as we will see later.