J Archaeol Sci 29 (7)

Mammalian erythrocytes or red blood cells -- whose presence in a smear is evidence for blood residues -- have been previously reported on prehistoric implements estimated to be approximately two million years old. On the basis of the Principle of Actualism, bloodstains from modern human individuals were obtained on obsidian, limestone and chert. Then, they were stored in a unsterile room under microclimatically unmanipulated fluctuating conditions, for lengths of time ranging from 7 years, 6 months to 10 years, 2 months. Afterwards, the bloodstains were coated with both carbon and gold and then examined by a scanning electron microscope (SEM). Results revealed a time-independent preservation of erythrocyte integrity, displaying moon-like shapes, and negative replicas. These results agree with several previously reported SEM analyses of younger mammalian bloodstains on chert and materials other than obsidian and limestone, and lead to consider the moon-like shapes and negative replicas as the genuine red blood cell morphologies characteristic of (at least mammalian) bloodstains.