A practical approach to the identification of low temperature heated bone using TEM

Unlike burnt bone, cooked bone leaves no obvious trace. The ability to identify cooked bone has far reaching implications within the fields of palaeo-anthropology, archaeology and forensic science. There is, however, only limited literature on low temperature heated bone. This is not due to a lack of significance, but from an absence of any means of identifying such heating at temperatures insufficient to cause charring. The situation is further complicated by the fact that diagenetic alteration to bone may mimic heat induced changes.

A previous Transmission Electron Microscopy (TEM) study showed that heat induced morphological changes to the collagen fibrils occur after low temperature heating of fish bone. This paper investigates whether these findings could be replicated on mammal bone. A series of experiments were carried out using sheep humeri. These results were compared with cooked and uncooked bones recovered from experimental burials, representing a variety of different environments (moorland, woodland and garden soil). Morphological changes to the fibrils were seen following only very mild heating events, such as short-term roasting of fleshed bone. However, similar changes were observed in unheated bone which had been buried in a low pH (3.5–4.5) soil for 7 years. Within a given burial cooked and uncooked bone was easily distinguishable. The technique, therefore, has direct application in forensic studies and may be of value in distinguishing heated from unheated bone within a given archaeological assemblage.