Once ironmasters understood how to use mineral coal in place of charcoal for converting pig to bar iron and for smelting, they adopted the new fuel where coal was avauilable at low cost and the demand for their iron sufficient to justify investment in new plant and equipment... Ironmasters could not make wrought iron with mineral coal in either a bloomery or a finery because the fuel, in direct contact with the metal, contaminated it with sulfur...In the original form of the process, the puddler melted pig iron on the hearth of the furnace and then used the air that passed through the furnace with the flame from the firebox to oxidize the silicon and carbon in the metal. As the puddler purified the iron, it began to solidify, and he had to exert his full strength to manipulate it. He divided the decarburized metal into several 'puddle balls', lumps of solid iron and liquid slag that he pulled from the furnace and hammered or squeezed to consolidate and force out the excess slag, just as bloomers or finers did with their loups...
(from Robert B. Gordon American Iron 1607-1900 [Johns Hopkins Press 1996, pp 133-134]
TN704 .N5 G67 1996)