Experimental Study of White Heat Line Formation in Burned Bone Using Fourier Transform Infrared Spectroscopy

In anthropological analysis of burned bone, the presence of a white heat line (WHL) aids in determining a bone’s physical condition prior to burning, distinguishing between those burned fleshed or wet versus dry, making this thermal signature an important source of information regarding the relative timing of burning. While the relationship between WHLs and a bone’s physical condition has been studied, there is a lack of research concerning WHL chemical composition. The present study assessed the composition of WHLs that form on burned bone using Fourier Transform Infrared Spectroscopy (FTIR), including the effects of soft tissue and retention of bone’s organic material on a WHL’s development and appearance. Experimental remains consisted of isolated bones from pig (Sus scrofa), sheep (Ovis aries), white-tailed deer (Odocoileus virginianus), and elk (Cervus elaphus) in five physical conditions: fleshed, defleshed/very wet, partially wet, dry, and dry/soaked. Chemical composition was analyzed using spectral peak heights of the carbonate (CO3) ν3 (1415 cm-1), phosphate (PO4) ν3 (1035 cm-1), and amide I (1660 cm-1) vibrational bands. WHLs formed on 8 of 16 bones burned fleshed (50%) compared to 8 of 27 defleshed/very wet (29.6%). The partially wet, dry, and dry/soaked sample groups did not develop a WHL. Results indicate WHLs that formed on fleshed bone contained an increased amount of CO3, PO4, and amide I versus unburned controls. In contrast, WHLs that formed on defleshed/very wet bone contained decreased amounts. Additional research is needed to explore the exact mechanisms causing the formation of WHLs and their physical appearance.