This piece of skull was part of a trepanation experiment which used an obsidian knife to create the hole. Obsidian is a naturally occurring volcanic glass. It is a hard wearing material and can cut through materials such as marble and bone. The hole produced is 19 mm in diameter. The inscriptions tells us that it took half an hour to produce the hole and that the skull belonged to a 44-year-old male. This experiment was carried out by Thomas Wilson Parry (1866-1945), an English doctor who was interested in the tools and techniques of Neolithic trepanation. Parry collected skulls from around the world and experimented on them with different types of tools. Supplied by the Science Museum, London, courtesy of Wellcome Images.