Cementation Process

The cementation process was an obsolete method of making steel by carburizing iron, packing iron bars together with charcoal in sealed stone pots and heating them for a week or more so carbon from the charcoal diffused into the iron's surface, before letting the pots cool for roughly two more weeks. A 1574 treatise written in Prague described the method, the German metalworker Johann Nussbaum is credited with inventing it and began operating it in Nuremberg in 1601, and William Ellyot and Mathias Meysey patented the process in England in 1614. The English ironmaster Basil Brooke acquired the English patent but was forced to surrender it in 1619 after he could not supply enough good-quality steel to meet demand, operating furnaces later confirmed by archaeological evidence at Coalbrookdale; the resulting bars, called blister steel because carbon absorption left blisters on their surface, gained a little over one percent in mass from the carbon and could be forge-welded together into the higher-quality shear steel or melted down into crucible steel.