Autofluorescence of experimentally heated bone: Potential archaeological applications and relevance for estimating degree of burning

Assessing the degree of burning in archaeological bone is important for interpreting fire-related activities of humans in the past. Previous studies have explored a range of analytical methods to characterise burned bone, examining heat-induced changes to specific physical- or chemical properties. Autofluorescence is a property of bone tissue that has not received much attention in archaeological research despite its applicability on both hand-specimens and microscopic fragments in sediment thin-sections. In this study epifluorescence microscopy with blue-light excitation (400–440 nm) is applied in combination with fluorescence spectroscopy to investigate autofluorescence of experimentally heated cow bone. The results show that upon heating, a shift in fluorescence colour – from blueish-green to yellowish-green – occurs before combustion or charring, lasting up to the moment of calcination. The associated emission spectra suggest that this shift is caused by either or both the presence of pyrolysis products and changes to the bone mineral structure. These results support the use of epifluorescence microscopy as an analytical method for archaeology and contribute to a growing set of multi-proxy reference data to assess the degree of burning of bone.