Investigating responses of archaeological bone to post-retrieval environment

Archaeological bones are an irreplaceable resource, especially with interest in newer molecular study techniques. Whilst burial environments predictably affect mineral and protein contents and physical integrity (“preservation state”) of retrieved bones, effects of post-retrieval environment are not well characterised, and curatorial guidelines are non-specific.The established Oxford histological Index (OHI) was used with a novel application of a mechanical competence test to link preservation state of archaeological bones to responses to fluctuating relative humidity (RH) in a simulated post-retrieval environment.Archaeological ovine metapodials were classified as physically “poor”, “medium” and “well” preserved. Resin-embedded thin sections of each bone were examined histologically; neighbouring segments were subjected to low force hardness (Vickers “micro-hardness”) testing. Adjacent segments were then exposed to fluctuating RH in a controlled environment, after which histology and micro-hardness testing were again performed.Initial preservation states reflected collagen retention, with “best preserved” bones having most collagen. The ability to withstand fluctuating RH was inversely related to collagen-retention, with cracking (gross and micro-) more likely in better preserved bones. Similarly, micro-hardness tended to decrease in better preserved bones after exposure to fluctuating RH; an effect not echoed by poorer preserved bones. The differing resilience of the bones may relate to hygroscopicity of collagen, also to facilitation of microbiological growth by fluctuating RH in better preserved bones.This project is part of ongoing investigations into post-retrieval deterioration of archaeological bone and in the longer term aims to aid curators to provide optimal environments for bones in their care.