Having been introduced to the technique of shot making during his stay in England, Simon Wallner built a shot tower in 1814 (first of wood, later of stone). In a shot tower, lead is heated until molten, then dropped through a copper sieve high up in the tower. The liquid lead solidifies as it falls and by surface tension forms tiny spherical balls. The partially cooled balls are caught at the floor of the tower in a water-filled basin. The now fully cooled balls are checked for roundness and sorted by size; those that are "out of round" are remelted. The business was closed in 1975.