The puddling furnace is a metalmaking technology used to create wrought iron or steel from the pig iron produced in a blast furnace. The furnace is constructed to pull the hot air over the iron without the fuel coming into direct contact with the iron, a system generally known as a reverberatory furnace or open hearth furnace .

The production of a puddling furnace was essentially governed by how much weight a man could lift with a ball of puddled iron generally weighing about 5cwt (about 250kg!). Puddlers often had to retire and find other jobs due to injury.

For comparison, an average size charge for a puddling furnace was 600 lb (270 kg), for a Bessemer converter it is 15 short tons (13 600 kg). The puddling process could not be scaled up, being limited by the amount that the puddler could handle.

Only the wrought-iron races can do the work. All this I felt but could not say in the days when I piled the pig-iron in the puddling furnace and turned with boyish eagerness to have my father show me how. Six hundred pounds was the weight of pig-iron we used to put into a single hearth.