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.This is rarely justified for authentication, since our normal tests are usually fully sufficient to identify modern imitations.Analysis of our results shows that 92% of our tests either give ages consistent with those expected within the 20% limits or the piece is modern.If you don’t find the answer to your query here please do not hesitate to contact us and we will be in touch. An authenticity test is not the same as dating an archaeological site where the object is excavated under controlled conditions and the theoretical limit of accuracy is ±6%.
Under most circumstances this is sufficient to distinguish an 18th century piece from a modern copy or a 17th century piece from a 19th century copy.
Porcelain is very hard and has to be cut using a diamond drill under running water to keep the sample cool. A hollow core drill is the safest way of doing this.
The core is cut into thin slices using a fine, water-cooled diamond blade and the slices used for TL (pre-dose) measurements.
We can only date an object if it has been excavated under controlled conditions and if we can monitor the burial site in situ.
If a large number of fragments in each location is dated, a mean value for that location can be computed. So much information has been lost by the time an object reaches the art market that the quoted age limits cannot realistically be better ±20%.