First Results on Understanding the Shiny Surfaces of Heat-Treated Chert

In Europe, intentional heat treatment of silica rocks to improve their knapping quality appeared for the first time during the Solutrean (ca 25.5-23 ka cal BP). The recognition of heat-treated artefacts in assemblages is based on macroscopic criteria like shiny luster. Surface luster or gloss, however, may be prone to observer bias and calls for more objectives measures to quantify it. In this study, we use a laser scanning microscope to measure the micro-relief on surfaces knapped after heat treatment at different temperatures. Our results show the evolution of the roughness of fresh fracture surface as a function of heating temperatures. Roughness appears to be a good proxy for macroscopically observable surface gloss caused by heat treatment. Such Ra measurements even bear the potential to become a new tool for the recognition of heat treatment.