Puddling is a technique, perfected by Henry Cort in
1784, for making pure iron from pig iron.
By the mid-1700's, there arose a need for higher quality iron. The method
used to refine charcoal iron was called "Puddling." Bars of
charcoal iron were heated in a furnace by an indirect coal fire. Molten iron
was then cast into ingots (pigs) and stacked one way the other in a pile on
the Puddling hearth. Here it was heated and "puddled" to remove
impurities (the "puddlers" stirred the liquid). Impurities burned
off and the puddled iron formed pasty balls.
Puddled iron was then transferred to the shingling hammer (a gigantic power
hammer which was capable of earth-shattering blows) which formed the iron
into a billet. This was then rolled, cut up into lengths, re-stacked and the
whole process repeated over again. The more times the process was repeated,
the better was the quality of the finished wrought iron.
Puddling superseded wrought iron working by hand and the introduction of
the technique made a significant contribution to the industrial revolution.