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The process involved pouring hot pitch, or tar (mainly used at the time for lighting purposes), into a conical shaped paper "cap", which was forced onto a bound suspect's head, allowed to cool, then rapidly removed, taking with it a portion of the suspect's skin and tissue. Less elaborate versions included smearing a cloth or piece of paper with pitch and pressing onto the head of the intended victim.
The torture was usually preceded by the crude shearing of the victim's hair/scalp. The effect on the skull of this controlled form of local boiling somewhat resembles scalping, earlier known as a practice used on natives of the North American colonies by resident American Indians. Pitch has long, even in antiquity, been used (like other hot liquids, even melted metal) to pour into a victim's orifices. However, both those techniques were usually faster and often lethal, so less suitable as torture proper, rather as capital punishment.