Any of the methods used to strike a flake from a core in the making of stone tools; the reduction of a stone core by hitting it with a hammerstone or bone. Direct percussion is hitting a core with a hammer. Indirect percussion uses a punch between the core and the hammer. Anvil percussion (block on block) is the striking of a core against a fixed hardstone anvil. Bipolar percussion involves resting the core on an anvil and striking it with a hammer, making a flake with a bulb of percussion on each end.