Thermoluminescence

• Basic principle

Certain crystals such as quartz, feldspar or zirconium, accumulate natural and cosmic radiation from their environment over the course of time. If they are heated to a very high temperature, they release this accumulated energy in the form of light. Once re-cooled, the accumulation starts again, and the counter is reset to zero. (source Wikipedia)

• Practical use

By heating the crystals found in pottery materials, the energy charge that has accumulated over geological time is released. The light emitted by subjecting a sample to high temperatures can be measured, and it is proportional to the time passed between the two operations. Taking into account the natural level of radiation of the medium, the location where the sample was found, and the nature of the crystals concerned, a precise dating of the sample is obtained. This technique can be used as effectively to date hearth, furnace and kiln material as it is to date lava, and generally any medium possessing sensitive crystals and having been subjected to high temperatures in the past.

• Limitations of this method

The measurement could be distorted by an unknown event which might have heated the sample to a high temperature, such as a fire. For the dating of a potter's kiln, the result will reflect the last use of the kiln. In addition, an accidental exposure of the sample to a radioactive source would scramble the calculations definitively.

The crystals are naturally limited in their capacity to store the natural radioactivity, and beyond a certain threshold, they no longer react. The maximum measurable age is approximately 700,000 years.

• Our methods

Taking a small sample of argillaceous matter from the piece, such as feldspar crystals or quartz, and heating it to 500° C, as is done in the creation process of all types of terrracotta, resets the natural time clock. Just a few grams are enough for an effective sample. This sample is crushed, then cleaned by a series of chemicals. The luminescence given off is then recorded. An initial study of a statue is done to choose at least two areas from which to collect samples that will not damage the statue. More than one sample allows us to compare the results, and make sure that the piece is homogeneous, i.e. that it has not been reworked or reconstructed. The vast majority of the pieces presented in our gallery were successfully verified using this method by ARCHEOLABS, a well-known expert independent organization, and we guarantee that the integrity of every piece has been preserved. Art effectively meets science, and the resulting satisfaction is a true pleasure.

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