FEATURE 102 Authentic Reflections By Olivier Langevin, Archaeometrist. Director of the Thermoluminescence Laboratory at QED Laboratory A legitimate question that should be posed with regard to every work of art is that of its authenticity. Raising the subject may be impolite, injurious, or even offensive, and it may make us appear ignorant, but it is fundamental, especially since there are so many pseudo-scientific publications on objects of highly dubious authenticity. Obviously, stylistic expertise is essential, but what we might refer to as the “pedigree expert”—that is, one who will venture no opinion about a work without three generations of provenance, documentation, and receipts—is useless. It is better to find an expert who loves the art, whose knowledge is not rigid, and who recognizes that he is just human. Typology has limits with regard to any given object, and our “sensitive expert” is generally straightforward about this. In the case of so-called “Djenne” objects, the first thing that usually comes to mind is a kneeling figure with its arms crossed over its chest and its body covered with snakes or pustules. The corpus of these works is actually quite varied, and the inspiration for these sculptors does not seem to have any limits to our Western eyes. The terracottas presented in this article by Anne-Marie Bouttiaux and Marc Ghysels are remarkable examples of the richness of ancient Mali’s cultures. The suspicion that surprise engenders rapidly turns to astonishment, and ultimately culminates in reflection. Science must no longer stand on the sidelines with regard to issues of authenticity, since science is a tool that is an integral part of this investigation, but what information it can provide must be clearly understood. In many cases, dating by thermoluminescence is an appropriate first step. This method involves calculating the dose of natural radiation received by a terracotta since its last firing, which is known as its archaeological dose. This provides a record of time. To determine the date of firing, the archaeological dose is divided by the amount of radiation that the terracotta receives in a year. It is important to remember that the result obtained will not be a fixed date but rather date ranges. This is because thermoluminescence relies on radioactive phenomena and thus deals in probabilities rather than certainties. The annual dose depends upon the mineralogical composition of the terracotta and that of the earth it was buried in. Since the place where it was excavated is generally inaccessible, the annual dose cannot be precisely measured and instead must be estimated. For thermoluminescence, “Djenne” terracottas can be seen as a textbook case. The area in which these terracottas were produced, the Inland Niger Delta, is, for the time frames we are considering, extremely stable from a geological perspective. It is composed of alluvial plains that are regularly flooded during the rainy season. Thus there is a relatively high degree of homogeneity both in the mineralogical composition of the objects and in the environment in which they are buried, and the annual dose can be estimated with considerable precision. The results obtained have a high degree of reliability, and this has made it possible to date the “Djenne” culture very precisely to between AD 1100 and 1600. Despite our confidence in the dating of these terracottas by thermoluminescence, the works that the “Scrofulous Sogolon” article address are not accompanied by precise dates. The reason for this is nothing more than an abundance of scientific caution and prudence on the part of its authors; however, the reader should be assured that these terracottas have been carefully analyzed using thermoluminescence techniques. For logistical reasons, various laboratories divided up the work. Because each of them used its own study protocols, the comparison of the dating results in this context is difficult because the complexity and variety of the results obtained require special effort to standardize, which is a laborious process, to say the least. Thermoluminescence relies on samples rather than an analysis of the entire piece. In order to avoid problems relating to sampling, we recommend additional study with X-ray scanning. This article by Bouttiaux and Ghysels is a convincing elucidation of the scanner’s usefulness and pertinence. In addition to detecting possible restorations, both minor and major, this second method of study reveals a fuller understanding of the genesis of the object. When examinations by thermoluminescence and by scanner yield compatible results vis-à-vis the time period and culture under consideration, a significant step toward the determination of authenticity has been achieved. This is all the more so when the “sensitive expert” confirms those results. Only an enriching, pluridisciplinary approach involving a number of specialists can culminate in a well-supported and correct conclusion. As for the above-mentioned “pedigree expert,” he will never know the simple joy that this exercise brings.
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