Sweating. A removal of metal from a coin for the scrap metal (like clipping and filing). Once introduced into circulation gold and silver coins were vulnerable to this practice by unscrupulous people during and after the middle ages. Hammered coins, which did not have a well defined edge or rim encouraged this practice. Removing a little metal from a number of coins – then passing them again at their initial value – would result in illgotten gains.

Sweating was accomplished by placing several precious metal coins in a leather bag and shaking it vigorously (the same method Matthew Boulton used for deburring blanks). Enough metal adheres to the leather inside to make the effort worthwhile. Clipping and filing was metal removed from the edge of coins. The development of coins in perfect circular form with rims, borders and reeded edges helped to prohibit these practices.

Reference:

NM42 {1982} Doty, p 319.