Chert and heat-treated silcrete artefacts in Mertenhof.

(a-g): Different types of chert in the analysed Mertenhof assemblages. (h): Surface of unaltered and experimentally heat-treated silcrete showing the colour change upon heating. (j): Untransformed Mertenhof silcrete of the yellow type to which no heat treatment was applied. (i, k): Artefacts made from this same silcrete type that were heat-treated. (l): Mertenhof artefact made from grey silcrete. (m): the contrast between a pre- and a post-heating scar on the same artefact showing the difference of roughness. (a-g) and (i-l) all have the same scale. Note that the roughness of the surfaces in artefacts (i-l) cannot be estimated in these photos that were taken with frontal light.