From the British Museum site, which is a goldmine of fabulous images, the death mask of Oliver Cromwell:
The BM’s blurb seems worth quoting in full.
When a famous person died, a death mask was often taken as a permanent and precise record of the way they looked. An initial cast provided a mould from which subsequent plaster or wax death masks could be taken. Death masks were widely distributed through private and public collections and were also used as models for posthumous portraits, whether painted or sculpted. This example was originally owned by Sir Hans Sloane (1660-1753) whose collection contributed to the founding of the British Museum in 1753.
It was important that a death mask was made as soon as possible after death so that the character of the deceased was captured before the features started to fall. The death mask of Oliver Cromwell (1599-1658) was taken after the embalmment of his body and it shows the cloth bound around his head to cover the cincture. The face has a beardlet and moustache, but Cromwell’s famous wart has either been pared off or has disappeared due to the action of the embalming fluid. Several casts of Cromwell’s death masks exist. Although the identification of this example has been questioned, it certainly entered the Museum as a representation of Cromwell. Cromwell was initially buried in Westminster Abbey but his body was exhumed after the Restoration and hung on Tyburn gallows and his head was displayed on a pole. Apparently, his head was later sold many times until it came into the possession of the Wilkinson family in the nineteenth century. It was finally buried in a Cambridge college in the 1960s.