Detecting heat treatment on silcrete: Experiments with methods

Abstract

We describe experiments aimed at detecting heat treatment of silcrete, a siliceous rock of inhomogeneous lithology widely used in prehistoric Australia. Our samples (N= 66) come from eastern New South Wales. Two methods widely used on other materials are found to be inadequate: scanning electron microscope (SEM) analyses allow conflicting interpretations of the same piece of material, while colour changes are too variable to be a reliable indicator. Two other methods are more reliable: increase in lustre is rare, but clearly indicates heat treatment when its thermal origin is certain; palaeomagnetism assessments of modern (N=18) and archaeological (N= 23) samples show that while the method does not give false positives, it indicates heating and not necessarily heat treatment. A combination of palaeomagnetism and lustre assessments is recommended. © 1997 Academic Press Limited.