Is vitrification in charcoal a result of high temperature burning of wood?

The term ‘vitrified’ is used to describe the glassy appearance of some charcoals recovered in the archaeological record. It has been generally considered that this phenomenon is a result of wood being subjected to high temperatures similar to the role of temperature in the formation of glass and pottery. Charcoals displaying characteristics of vitrification from three distinct archaeological contexts were analysed using reflectance microscopy to determine their temperature of formation. Charcoal was also generated in laboratory charring experiments at temperatures of 900–1100 °C for durations of 1, 6, 12 and 24 h to determine if subjection to high temperature led to vitrification. None of the laboratory-produced charcoals displayed characteristics of vitrification. Mean random reflectance of the vitrified archaeological fragments indicated temperature of formation from 310 to 530 °C. A charring experiment was also conducted, at 500 °C for 6 h, using green wood with some bark attached, and added sugars, but no evidence of vitrification was seen. Therefore vitrified charcoals do not result from high temperature charring or primarily from the use of green wood.