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date: 26 April 2019

Heat Treatment

This is an advance summary of a forthcoming article in the Oxford Research Encyclopedia of Anthropology. Please check back later for the full article.

In archaeology, heat treatment is the intentional transformation of stone (normally sedimentary silica rocks) using fire to produce materials with improved fracture properties. It has been documented on all continents, from the African Middle Stone Age until sub-recent times. It was an important part of the Mediterranean Neolithic, and it sporadically appeared in the Palaeolithic and Mesolithic of Asia and Europe. It may have been part of the knowledge of people first colonizing North and South America, and it played an important role for tool making in Australian Prehistory. In all these contexts, heat treatment was normally used to improve the quality of stone raw materials for tool knapping—its association with pressure flaking has been highlighted—but a few examples also document the quest for making tools with improved qualities (shaper cutting edges) and intentional segmentation of large blocks of raw material to produce smaller, more usable modules (fire-fracturing). Two categories of silica rocks were most often heat-treated throughout prehistory: relatively fine-grained marine chert or flint, and more coarse-grained continental silcrete. The finding of stone heat treatment in archaeological contexts opens up several research questions on its role for tool making, its cognitive and social implications, or the investment it required. There are important avenues for research—for example: Why did people heat-treat stone? What happens to stones when heated? How can heating be recognized? By what technical means were stones heated? What cost did heat treatment represent for its instigators? Answering these questions will shed light on archaeologically relevant processes like innovation, re-invention, convergence, or the advent of complexity. The methods needed to produce the answers, however, often stem from other fields like physics, chemistry, mineralogy, or material sciences.