Swept under the rug: the problem of unacknowledged ambiguity in lithic residue identification

► The morphology of organic residues on stone tools can be ambiguous. ► We study the nature of this ambiguity in a reference collection of residues. ► We find that certain residue types are more ambiguous than others. ► These include hide-scraping, bone-scraping, and hardwood-whittling residues. ► Multiple types of microscopy (light, electron) may help diminish the number of ambiguous cases.