Use-related or contamination? Residue and use-wear mapping on stone tools used for experimental processing of plants from Southeast Asia

Analysing residues on stone tools can reveal precise information about the activities that were conducted with the lithic tool and is a valuable technique to reconstruct past human behaviours. However, it is often difficult to assess the nature of the relationship between a residue and the artefact on which it is found. It is of great importance, therefore, to determine whether residues are use-related or a result of contamination. Here, we conducted experiments with 99 tool replicas made of red jasper, processed 15 different plant taxa and mapped the distribution of residues against the use-wear traces. Our experiments addressed several questions on the spatial relationship between use-wear and use-related residues on stone tools. In the majority of cases the residues were not spatially associated with use-wear. Therefore, it appears that residues should not necessarily be considered as non-related to use because they are not in close proximity to use-wear. On the other hand, our experiments also showed that the problem of contamination should not be underestimated and can be a serious cause for misinterpreting stone tool functions. Finally, our results showed a variability in residue distribution between tools used to process different plant taxa and revealed that the water content in the contact material has an influence on residue distribution.