The introduction of the blast furnaceA blast furnace is a type of furnace for smelting whereby the combustion material and ore are supplied with air in the centre of the chamber such that the chemical reaction does not take place only at the surface. Typically this is used for the production of iron and steel. Blast furnace technology has arisen at a number of points in history, only to be lost again. Abraham Darby in 1709 changed ironmaking by replacing charcoal with the much less expensive coke. Not only was the fuel much cheaper, but it also could be burned in a "lump" instead of a thin sheet, allowing the furnaces to be much larger. Soon iron prices were dropping rapidly as production shot up. However the product of a blast furnace, pig iron, had a very high carbon content and was very brittle. In order to use it in ironmongery, it had to first be converted to a form similar to what the bloom/wrought process produced. This process took time to develop, but by the 1750s a number of oxides had been identified that would react with the excess carbon to produce carbon dioxide, which then bubbles out. Historically, this would be followed by faggoting. Wrought iron which had been faggoted twice was referred to as "Best"; if faggoted again it would become "Best Best", then "Treble best", etc. Faggoting resulted in impurities within the metal ending
up as long thin inclusions, creating a grain within the metal. "Best" bars would have a tensile strength
along the grain of about 23 tons per square inch. "Treble best" could reach
28 tons per square inch. The strengths across the grain would be about 15%
lower
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