Burning bodies to ashes

[mozi]

First of all, the process should be slow (unless you are in a raging fire) and when your dead body burns away it will leave behind some things:

temperatures of 870–980 °C (1,600–1,800 °F) to ensure disintegration of the corpse.
...

The time required for cremation varies from body to body, and, in modern furnaces, the process may be as fast as one hour per 45 kg (100 lb) of body weight.