https://quatr.us/history/bellows-invented-bellows.htm   By 400 BC, people in China used ox-hide bellows. They were using more efficient double-action piston box bellows by the early Han Dynasty, about 200 BC. These bellows blow air both when they’re opened and when they’re closed, so they’re more efficient than the pot bellows.   The double action ( simultaneously closing and opening ) is a rather important improvement, especially for metalurgy ( alchemy ) and producing consistent even smooth temperatures for tempering.