Bloomery type furnaces typically produced a range of iron products from very low carbon iron to steel containing approximately 0.2% to 1.5% carbon. The master smith had to select bits of low carbon iron, carburize them, and pattern-weld them together to make steel sheets. Even when applied to a non-carburized bloom, this pound, fold and weld process resulted in a more homogeneous product and removed much of the slag. The process had to be repeated up to 15 times when high quality steel was needed, as for a sword. The alternative was to carburize the surface of a finished product. Each welding's heat oxidises some carbon, so the master smith had to make sure there was enough carbon in the starting mixture.