The heavy hammer-blows effectively squeezed the slag out of the refined iron necessary to achieve highest quality as well as shaped the iron into blooms for the subsequent hot rolling.
The hammer is powered by the big water wheel. The inlet of water and the speed is controlled by the leveler to the right. Typical speed is 60 strokes per minute.

As protection against the heat the forgemen were wearing these white and loosely fitting long shirts. Also the legs had to be protected against sparks and red hot particles.