Rather yield than break: assessing the influence of human bone collagen content on heat-induced warping through vibrational spectroscopy

Warping has been used to determine the pre-burning condition of human skeletal remains. In the literature, this modification has been associated more often with the burning of fleshed and green bones, but it also arises during the burning of dry bones. The objective of this paper was to assess if bone collagen content has a significant effect on the occurrence of warping in a sample of experimentally burned human bones. The presence of collagen was analyzed in two different samples through a vibrational spectroscopy technology—FTIR. One of them was composed of 40 archeological bones from the seventeenth to twentieth centuries ad. The other one was composed of bones from 14 skeletons belonging to the 21st century identified skeletal collection. The results confirmed that the amide I band assigned to the collagen was much more intense in bones presenting heat-induced warping. Nonetheless, although significant (p = 0.040), the collagen content was not as useful as other variables to the regression model we proposed for explaining warping. Factors such as the maximum temperature (p < 0.001) and burning time (p = 0.001) contributed more significantly. Results demonstrated that the mere preservation of collagen is not enough to explain warping. Burning dynamics seem to have an important role as well although we failed to clearly document its specificities. Other factors such as the asymmetric distribution of collagen and other components within bone, the gravity force, the shape of the bone, and the position in which it is burned may also play an important role on heat-induced changes and require further analysis.