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Heat Treatment

Flint Knapping and Heat Treatment

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An experimental heat treatment fire built over sand that contains silcrete stone nodules.

An experimental heat treatment fire built over sand that contains silcrete stone nodules.

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Heat treatment in stone tool making (or flint knapping) refers to the controlled use of fire on raw lithic material to improve its flaking quality. Stone tools are made by a controlled series of blows of different weights and expression by other pieces of stone, antler and bone tools. the blows slowly (or rapidly) remove small pieces, called wasteflakes or debitage, as the flint knapper works his or her way to a finished tool.

The best type of lithic raw material to use is fine grained siliceous lithic materials, and ethnographic and experimental studies have shown that heating that raw material to between 300-450 degrees centigrade (a wood or charcoal fire does that) changes the stone, allowing the resulting fractures to follow the natural grain of the stone, rather than breaking across the grain.

In addition to changes in the fracturing properties, heat treatment may change the stone's color and increase its lustre. Other measurable changes include mineralogical changes in texture and converts siderite to magnetite or hematite. Thus, heating rocks can change their magnetic properties (which is the underlying theory behind archaeomagnetism dating).

The oldest possible evidence for heat-treatment of lithic raw material dates to the Middle Stone Age site of Pinnacle Point, South Africa. The Pinnacle Point data showed clear evidence of heat-treatment in artifacts from the 71,000 bp occupations, and a suggestion of the same in the 164,000 bp occupation.

Sources

This glossary entry is a part of the About.com Guide to Lithics and Lithic Analysis and part of the Dictionary of Archaeology.

Behm, Jeffrey A. and Alaric Faulkner 1973 Hixton quartzite: Experiments in heat treatment. Wisconsin Archeologist 55(4):271-276.

Borradaile, G. J., et al. 1993 Magnetic and optical methods for detecting the heat treatment of chert. Journal of Archaeological Science 20:57-66.

Brown, Kyle S., et al. 2009 Fire As an Engineering Tool of Early Modern Humans. Science 325:859-862.

Crabtree, B. and B. R. Butler 1964 Notes on experiments in flint knapping: heat treatment of silica minerals. Tebiwa 7:1-6.

Domanski, Marian and John A. Webb 1992 Effect of heat treatment on siliceous rocks used in prehistoric lithic technology. Journal of Archaeological Science 19:601-614.

Dunnell, Robert C., McCutcheon, M. Ikeya, and S. Toyoda 1994 Heat treatment of Mill Creek and Dover cherts on the Malden plain, southeast Missouri. Journal of Archaeological Science 21:73-89.

Enzo, Stefano, et al. 2007 A study by thermal treatment and X-ray powder diffraction on burnt fragmented bones from tombs II, IV and IX belonging to the hypogeic necropolis of "Sa Figu" near Ittiri, Sassari (Sardinia, Italy). Journal of Archaeological Science 34:1731-1737.

Mandeville, M. D. 1973 A consideration of the thermal pretreatment of chert. Plains Anthropologist 18(61):177-202.

Patterson, Leland W. 1979 Quantative Characteristics of Debitage From Heat Treated Chert. Plains Anthropologist 24(85):255-259.

Patterson, Leland W. 1982 Reply to McHugh and Mitchum on Experimental Heat Treating of Chert. Plains Anthropologist 27(96):171-172.

Schindler, Debra L., James W. Hatch, Conrad A. Hay, and Richard C. Bradt 1982 Aboriginal thermal alteration of a central Pennsylvania jasper: Analytical and behavioral implications. American Antiquity 47(3):526-544.

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