packed in alternating layers, with a top layer of charcoal and then refractory matter to make the pot or "coffin" airtight. Some manufacturers used a mixture of powdered charcoal, soot and mineral salts, called cement powder. In larger works, up to 16 tons of iron were treated in each cycle, though it can be done on a small scale, such as in a small furnace or blacksmith's forge. Depending on the thickness of the iron bars, the pots were then heated from below for a week or more. Bars were regularly examined and when the correct condition was reached the heat was withdrawn and the pots were left until cool—usually around fourteen days. The iron had gained a little over 1% in mass from the carbon in the charcoal, and had become heterogeneous bars of blister steel. The bars were then shortened, bound, heated and forge welded together to become shear steel. It would be cut and re welded multiple times, with each new weld producing a more homogeneous, higher quality steel. This would be done at most 3-4 times, as more is unnecessary and could potentially cause carbon loss from the steel. Alternatively they could be broken up and melted in a crucible using a crucible furnace with a flux to become crucible steel (at the time also called cast steel), a process devised by Benjamin Huntsman in Sheffield in the 1740s. Similar processes Brass production In the early modern period, brass, an alloy of copper and zinc, was usually produced by a cementation process in which metallic copper was heated with calamine, a zinc ore, to make calamine brass. Notes References K. C. Barraclough, Steel before Bessemer I: Blister Steel: The Birth of an Industry (1985). K. C. Barraclough, "Swedish Iron and Sheffield Steel", History of Technology 12 (1990), 1–39. Dorian Gerhold, "The steel industry in England, 1614-1740", in R.W. Hoyle (ed.), "Histories of people and landscape: essays on the Sheffield region in memory of David Hey" (2021), 65-86 P. W. King, "The Cartel in Oregrounds Iron", Journal of Industrial History 6 (2003), 25–48. R. J. MacKenzie and J. A Whiteman, "Why pay more? An archaeometallurgical examination of 19th century Swedish Wrought iron and Sheffield blister steel", Historical Metallurgy'' 40(2) (2006), 138–49. Steelmaking Metallurgical processes Obsolete technologies