Steel castings are made by pouring mild steel into molds. Crucible steel castings are made by melting bar blister steel in crucibles and pouring it into molds. Large steel castings, such as beams for stationary engines, steam chests, large shafts, pistons, cross-heads, stands for steam hammers, large stop valves, etc., are made by simply charging the furnace with pig iron, scrap steel, and broken ingot molds. The disadvantage of this process is that the castings are not perfectly sound because of pores or blow-holes below the surface of the metal which cannot be seen. When they are on the surface they can be eliminated in machining.