Potting and stamping is a modern name for one of the 18th-century processes for refining

pig iron Pig iron, also known as crude iron, is an intermediate product of the iron industry in the production of steel which is obtained by smelting iron ore in a blast furnace. Pig iron has a high carbon content, typically 3.8–4.7%, along with ...

without the use of

charcoal Charcoal is a lightweight black carbon residue produced by strongly heating wood (or other animal and plant materials) in minimal oxygen to remove all water and volatile constituents. In the traditional version of this pyrolysis process, ...

Inventors

The process was devised by Charles Wood of Lowmill, Egremont in

Cumberland Cumberland ( ) is a historic counties of England, historic county in the far North West England. It covers part of the Lake District as well as the north Pennines and Solway Firth coast. Cumberland had an administrative function from the 12th c ...

and his brother John Wood of

Wednesbury Wednesbury () is a market town in Sandwell in the county of West Midlands, England. It is located near the source of the River Tame. Historically part of Staffordshire in the Hundred of Offlow, at the 2011 Census the town had a population of 3 ...

and

patent A patent is a type of intellectual property that gives its owner the legal right to exclude others from making, using, or selling an invention for a limited period of time in exchange for publishing an enabling disclosure of the invention."A ...

ed by them in 1761 and 1763. The process was improved by John Wright and Joseph Jesson of

West Bromwich West Bromwich ( ) is a market town in the borough of Sandwell, West Midlands (county), West Midlands, England. Historic counties of England, Historically part of Staffordshire, it is north-west of Birmingham. West Bromwich is part of the area ...

, who also obtained a patent.

Process

The process involved the melting of pig iron in an oxidising atmosphere. The metal was then allowed to cool, broken up by stamping, and washed. The granulated iron was then heated in pots in a

reverberatory furnace A reverberatory furnace is a metallurgical or process furnace that isolates the material being processed from contact with the fuel, but not from contact with combustion gases. The term ''reverberation'' is used here in a generic sense of ''re ...

. The resultant bloom was then drawn out under a forge hammer in the usual way.

Adoption

During the 14-year term of the patents, the process was little used except by the inventors. However, from c.1785, shortly before Wright & Jesson's process came out of patent, it seems to have been adopted by many

ironmaster An ironmaster is the manager, and usually owner, of a forge or blast furnace for the processing of iron. It is a term mainly associated with the period of the Industrial Revolution, especially in Great Britain. The ironmaster was usually a large ...

s in the West Midlands. Professor Charles Hyde argues that the potting and stamping process was largely responsible for a 70% rise in

wrought iron Wrought iron is an iron alloy with a very low carbon content (less than 0.08%) in contrast to that of cast iron (2.1% to 4%). It is a semi-fused mass of iron with fibrous slag inclusions (up to 2% by weight), which give it a wood-like "grain" ...

production from 1750 to 1788. Ultimately, the process was replaced by puddling, though it remains unclear how quickly.

References

Steelmaking {{mech-engineering-stub