gems, ancient gems, corundum, treatments.6

The history of heat treatment falls within an interdisciplinary field of inquiry, involving the reconstruction of know-how from archaeological discoveries; drawing on pre-scientific written sources, when available—chiefly lapidaries, alchemical treatises, and technical recipe books; experimenting with the methods described in those texts; and conducting gemological analyses to determine whether the gemstones have been heat-treated. Until now, experiments and analyses have mainly been carried out in the archaeological sphere, primarily in prehistoric and protohistoric contexts, as part of research into the lithic industry. In contrast, this question has been scarcely addressed for later periods such as the Middle Ages and the modern era (5th century to the end of the 18th century). It is important to emphasize that in ancient texts, one finds both practices with actual effectiveness and magical practices rooted in belief and ritual—such as the use of goat’s blood to cut diamond, first mentioned by Pliny the Elder in Natural History (Book 37, Chapter 15, Section 3) in the 1st century, and later repeated in treatises on gems, even during the Renaissance. Furthermore, reconstructing these recipes is not always easy, as those who wrote them were not necessarily those who practiced them, and one must not underestimate the secretive nature of these valuable skills.