The fate of archaeological keratin fibres in a temperate burial context: microtaphonomy study of hairs from Marie de Bretagne (15th c., Orléans, France)

When exceptionally preserved, hairs, wools, the skin stratum corneum and avian feathers can provide a wealth of archaeological and paleontological information. Long-term preservation of their information potential lies in the taphonomy (long-term behaviour laws) of keratin-based fibres and films. Here, we study the microscopic properties of archaeological hairs from the mediaeval burial of Marie de Bretagne (15th c., Orléans, France) preserved in a temperate environment, using complementary laboratory and synchrotron-based analytical instruments. We show that (a) the fibrillar keratin content of hair is exceptionally well preserved yet with limited degradation of the hair outer cortex in some hair strands, (b) exceptional preservation is attributed to the diffusion of copper and lead in the hair, (c) a posteriori examination led to the discovery of fragments of copper-based artefacts. We propose a possible scenario that led to the preservation of these tissues and discuss the archaeological interpretation of the microtaphonomy of these bioarchaeological remains.