How reliable is the visual identification of heat treatment on silcrete? A quantitative verification with a new method

Heat treatment of silcrete was a major innovation in the southern African Middle Stone Age (MSA). It allowed for the first time to improve materials for tool knapping, and it may have represented an important step in the perception of natural resources as modifiable objects. Recognising heat treatment in silcrete assemblages is therefore a crucial step for archaeologists working on the MSA. Two different methods, gloss analysis and visual estimation of surface roughness, have so far been used to identify heat treatment. Although both methods have advantages in specific situations, only visual heating proxy classifications allow to count heated vs. not-heated artefacts in assemblages. However, no objective independent data on the reliability and reproducibility of visual classifications are available today. This paper presents a new and promising non-destructive way to measure surface roughness and to verify the reliability of visual classifications: the replica tape method. The results show a rather good reliability of visual classifications: only few pieces are misclassified (n = 3), and the results of both replica tape measurements and visual classification agree within a 3% error range. These results also lay out the foundations for future developments of replica tape measurements to make it a stand-alone method for identifying heat treatment within silcrete assemblages.