Light Microscopy of Microfractures in Burned Bone

Abstract

Bone color changes depending upon the taphonomic agents that affect it. Burning turns bone black, brown, blue, gray, and white as the bone’s temperature increases and collagen is lost. It also creates diagnostic fractures that are visible at the gross level. Usually heat-altered bone is readily identified as such, but there are times when dark organic stains can mimic bone that is charred black. This paper provides a means to observe and quantify microfractures in burned bone for those instances when macroscopic observations fail to clarify if a bone fragment is actually burned; specifically, it distinguishes charred from organically stained bone. It is based upon a study of 50 calcined (burned to a bright white), charred, and organically stained bone fragments (n = 150) that were viewed with a standard stereomicroscope at ×30. Microfractures are readily discerned on charred and calcined bones, being more common on the latter; they are not present on organically stained bone. Charred bones may have their cortical surfaces obscured by a microlayer of adhering soft tissues as well as by microflaking of the external circumferential lamella. Overall, the methods described here allow the detection of microfractures on bone using a very simple approach and readily available technology.