Methods of dating ancient pottery
TL is only one tool in the investigation for authenticity.It cannot give the complete picture although it can do many things.If there is organic material present, the spectrum will consist of a series of peaks and troughs corresponding to the different chemical compounds. We can test to see if a pigment contains a modern element or not, or uses some pigment not available at the time the object was supposed to be made.
However, in some cases, pots are exposed to high medical radiation doses intentionally, so as to increase the apparent radiation dose and hence to mislead as to the apparent age of the piece.We regularly test Kangxi porcelain, and Staffordshire ware pottery. Here the pieces were frequently copied in the 19th century and so that even these 19th century copies have a TL age.The latest pieces in this case would be the 17th century for reliable testing.The results of another small percentage of the tests lie just outside the 20% range, and there is little doubt whether these pieces are ancient or modern. The datable TL signal comes from quartz and feldspar crystals in the clay, the so-called TL minerals. However, if there are no TL minerals, or if there are other minerals which decompose on heating and produce TL, there will be a spurious signal that swamps the archaeological signal, so the piece cannot be dated. Sometimes we find that we get two different, inconsistent results. We do not issue any report and ask for more sample so that we can try to get a definite result.Of the remainder, some cannot be dated because of problems with the material sampled: there may be a spurious signal (see below), or there is contamination, or the samples are too insensitive to radiation. In authenticity testing, usually we want to distinguish between modern copies and original pieces.