Materialising Sheffield - re-presenting the past  
steel ingots

Benjamin Huntsman – Early Life

Benjamin Huntsman and the world of eighteenth-century science

Early Eighteenth-Century Steel Production


Industrial Secrecy and Espionage

6. Opposition of the Sheffield cutlers

7. Huntsman’s works at Handsworth and Attercliffe

Swedish Visits to the Attercliffe Works

The evolution of the Attercliffe Works in the later 18th Century


2. Benjamin Huntsman and the world of eighteenth-century science

At the time of Huntsman's experiments, very little was understood of the chemical or physical composition of metals. It had yet to be recognised that the difference between iron and steel lay in their relative carbon content, and the Phlogiston theory of Georg Ernst Stahl still held favour among scientists. In practice, the techniques of iron smelting and steel making were more an art than a science, developed in most cases by trial and error. Had Huntsman consulted any of the available scholarship on the subject of steel, he would have found little there to guide him.

Huntsman's profession demanded a range of mechanical and metallurgical skills, and his surviving clocks and watches include skilfully executed work in brass, steel, gold and silver. Huntsman would not necessarily have done all of the work himself, but a good working knowledge of these metals was essential, and he was no doubt familiar with their production, refining and alloying. Gold and silver were still assayed and refined by the centuries-old process of cupellation, which involved melting the impure metal with lead and a flux of various salts in small, porous bone-ash crucibles, or "cupels". The flux would react with the oxidised lead and any other base metals present, before being absorbed by the walls of the crucible, leaving behind a "button" of the purified precious metals. The temperatures required were easily attainable in an assaying furnace using charcoal as a fuel, the only limitation being the small scale of the operation.

It was known in practical terms that common blister steel suffered from a lack of homogeneity and unwanted impurities. During the cementation process, the outside of the bar absorbed more carbon than the centre, giving it a more "steely" character. Its texture also became coarser and more crystalline, and the body of the steel was peppered with tiny voids and fissures. The subsequent forging process gave the steel a more even character, although streaks of slag would always remain, resulting in a product that was variable in quality and never totally sound. Huntsman's aim was to apply the refining process to cementation steel, in the hope that it would be similarly "purified".
Steel, however, had not previously been brought to temperatures high enough to allow its complete fusion. Neither common cupels, nor the larger clay crucibles used for glass making or brass founding were able to withstand the intense heat required, or the attack of the molten metal on the walls of the vessel. Even if a suitable crucible were found, none of the furnaces then in use could have produce sufficient heat, in a controlled environment, to melt the steel. Huntsman, therefore, needed to develop both a new crucible and a new furnace.





illustration: Letter from Matthew Boulton

illustration: Huntsman Clock