Bloomery Conversion

a process of refining pig iron (removal of excess carbon, silicon, and manganese) to produce malleable bloomery (welding) iron. It originated in about the 14th century (simultaneously with the development of cast-iron production), existed until the 18th century, and was replaced by the more efficient puddling process.

Bloomery conversion was performed in a bloomery (refinery hearth), where ingots of pig iron were placed on a layer of burning charcoal above the tuyere zone. The pig iron melted and, dripping down through the oxidizing tuyere zone, was refined. The product thus produced accumulated at the bottom of the hearth, where it underwent additional decarbonization as a result of the oxidizing action of the ferrous slag, forming a bloom weighing 50–100 kg. The finished bloom was drawn from the hearth and forged to sinter and centrifuge (strip) the slag.