The Ancient Egyptians preserved the human body by drying it out with a salt-like substance called natron and applying plant resins to the skin. Both these processes darken the colour of the skin, and the few Egyptian paintings that depict mummification show mummies as entirely black. Osiris, the god of the dead and rebirth, is often portrayed with black skin – a colour also likened to the dark fertile mud of the River Nile. Arabs associated the dark resins with tar-like bitumen, which they called mummia; this is the origin of the word mummy.
Answered by Campbell Price, Manchester Museum.