Wikipedia says in the history of mummy brown that it used to involve the ground-up remains of Egyptian mummies. How did this get started and how prevalent was it? Were people so desperate for new paint colours that they just ground up anything they could think of?
Maybe even more strangely, the Wikipedia article says artists stopped using the colour in the 19th century once they found out what it was. Did artists really not know what was in "mummy brown" for 200 years?
Not useful in paint, but it was sometimes mixed into paints of any color. In the 19th Century, at the height of the Egyptology craze, ground up mummy was hot, especially in Western Europe. The grounds were used in paints, plasters, jewelry, and even drinks. It was popular and a status tool (similar to gilded items today, or gold flakes in alcohol).