Differential etching after lithic heat treatment: First results of an experimental study

Abstract

The practice of lithic heat treatment creates a combination of initial dull flake scars and subsequent smooth flake scars when the implement is finished after heating. Experiments were done to test the susceptibility of dull and smooth flake scars to etching. The points were etched in 40% hydrofluoric acid for either 40 or 60 seconds. In the 40 seconds experiment, the smooth flake scars of 9 (out of 25) heated points showed less etching than the dull flake scars or no etching at all. These artefacts formed a weathering pattern that is similar to double patina in reworked flints. Ten unheated control samples did not form differential weathering between different generations of flake scars. In the 60 seconds experiment 4 (out of 25) heated points showed some parts of the smooth surface to be less affected. Ten unheated control samples did not form differential weathering. The experiments show that sometimes smooth flake scars are more resistant to etching initially.
 In Scanning Electron Microscopy, flint artefacts are sometimes pre-treated with hydrofluoric acid. Heat treated flints are susceptible to differential weathering by hydrofluoric acid. Thus, pre-treatment with hydrofluoric acid of heat treated SEM samples can lead to surfaces that are etched to a different extent.
 The chemical etching in this study does not replicate any natural patination process. How heat treated lithics respond to natural weathering processes cannot be predicted. Further studies should produce natural patination and test selected artefacts in contexts of intentional heat treatment for signs of heating.