A death mask is a cast made of a person’s face after they die. The cast is usually made of wax, clay, or plaster, and the process has been around for centuries. Many death masks were used to remember the dead, but also as a useful tool for recognizing unidentified bodies.
Plaster casts are said to have been made to record the features of those who were executed. Many criminals then used aliases, and the only way of identifying them after death (before the use of photographs and fingerprints) was to keep these plaster likenesses. In addition, some, if not all the heads were probably made for doctors or phrenologists bent on providing theories about physiognomy of criminal types by examining the bumps and shape of a criminal’s head after its owner was dead.