text: The product of the blast furnace is pig iron, which contains 4–5% carbon and usually some silicon.  To produce a forgeable product a further process was needed, usually described as fining, rather than refining.  From the 16th century, this was undertaken in a finery forge.  At the end of the 18th century, this began to be replaced by puddling (in a puddling furnace), which was in turn gradually superseded by the production of mild steel by the Bessemer process.