RESIDUES ON STONE ARTIFACTS - STATE OF A SCIENTIFIC ART

It is a startling experience to look down a microscope at a stone tool - a real Palaeolithic artefact, not a modern thing or a replicated co py - and see on its flint surface grubby brown-red stains that look th e colour of old blood. is a consensus emerging from the archaeological scientists as to just what traces of, especially, biological material s do survive on ancient stone surfaces, where they can be reliably cha racterized and identified?