The pudding furnace is a metalmaking technique used to create wrought iron. Molten iron was vigorously stirred using a stiff iron rod known as a rabbling-bar to expose the molten metal to the oxygen in the air. The excess carbon in the iron is burnt out and the iron becomes malleable and weldable.
The puddler, using the rabbling-bar gathers the globular masses of iron together into puddle-balls of about 40kg each, and pulls them out of the furnace with a hook formed into the end of the bar. These are then hammered using a steam-hammer to weld them into compact masses of malleable iron, while breaking of chunks of impurities. The iron is then re-heated and rolled out into flat bars or round rods.
The pudding furnace was widely used as the first step in making cruicible steel as well. Wrought iron was packed in large stone boxes with a layer of charcoal powder between each bar, heated to very high temperatures for six days (plus two days for the furnace to heat up and another two to cool down before the metal could be removed) so that some of the carbon from the charcoal was transferred to the iron. The bars were then broken into small pieces, and melted in crucibles to produce steel.
Both processes, and the pudding furnace, were displaced with the introduction of the Bessemer Process, which produced similar quality steels for a fraction of the cost and time.
