Luminescence Techniques
Luminescence techniques makes use of electrons trapped between the valence and conduction bands in the crystalline structure of certain types of matter. They rely on optically sensitive electron traps, which are responsible for luminescence, which have been exposed to natural light before they were covered by any overlying layers in a material. These electron traps empty as they are exposed to light and the components of the materials used by the artist are completely reset. Once a material is covered by other layers, it is no longer exposed to light. This means the electron traps are filled with electrons produced by ionization due to natural nuclear radiation. It can be said that the luminescence clock begins counting time whenever these traps are emptied. In conservation, this means that when the materials of a work of art saw daylight last can be dated.
There are three main stimulated luminescence methods: 1) Thermoluminescence, 2) Optically Stimulated Luminescence and 3) Infrared Luminescence Stimulated. These techniques can date geological material, preparation (ground) materials, and some colors.