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Another important technique in testing samples from a historic or archaeological site is a process known as Thermoluminescence testing, which involves a principle that all objects absorb radiation from the environment.This process frees electrons within elements or minerals that remain caught within the item.Its use is now common in the authentication of old ceramic wares, for which it gives the approximate date of the last firing.An example of this can be seen in Rink and Bartoll, 2005.This is commonly done by measurement of the alpha radioactivity (the uranium and thorium content) and the potassium content (K-40 is a beta and gamma emitter) of the sample material.Often the gamma radiation field at the position of the sample material is measured, or it may be calculated from the alpha radioactivity and potassium content of the sample environment, and the cosmic ray dose is added in.Where there is a dip (a so-called "electron trap"), a free electron may be attracted and trapped.The flux of ionizing radiation—both from cosmic radiation and from natural radioactivity—excites electrons from atoms in the crystal lattice into the conduction band where they can move freely.

Ultraviolet light emitted by the sample is detected for measurement.Thermoluminescence dating (TL) is the determination, by means of measuring the accumulated radiation dose, of the time elapsed since material containing crystalline minerals was either heated (lava, ceramics) or exposed to sunlight (sediments).As a crystalline material is heated during measurements, the process of thermoluminescence starts.Therefore, at that point the thermoluminescence signal is zero.As time goes on, the ionizing radiation field around the material causes the trapped electrons to accumulate (Figure 2).