The investment in time needed for heat treatment of flint and chert

摘要

In archaeology, heat treatment is the process of intentionally modifying lithic raw materials to improve their knapping quality. Even though the nature and parameters of the thermal transformations in rocks like flint and chert have been the object of several recent studies, the investment in time needed for heat treatment remains poorly investigated. In our study using time-resolved in situ Raman spectroscopy, we investigate the progression of the reaction that drives the thermal transformations of flint and chert. We found that, although parameters like maximum temperature and heating rate are functions of the content of chemically bound water and pore space in the samples, the duration these samples must be held at maximum temperature is shorter than 1 h, regardless of the maximum heating temperature or the mineralogy of the sample. Combining our results with previously published data on other parameters needed for lithic heat treatment, we propose lower and upper limits of the investment in time required for different heating procedures and discuss their relation to the structure and volume of the heated rocks. The actual duration of heat treatment of flint and chert, as it was practised in different chrono-cultural periods, lies somewhere between 7 h and 2-3 days depending on the type of flint or chert and the heating environment used.