Derwentcote Steel furnace was built in the 1730s and was used for cementation, a process which converted wrought iron into steel.
The cementation process
It is one of the few complete examples of this type of furnace, and is the last surviving piece of evidence of cementation steelmaking in the north-east.
The conical chimney houses two sandstone chests into which iron bars were packed with alternate layers of charcoal powder.
When the fire was lit and the chests sealed, flames and heat travelled up through flues and chimneys around them, and temperatures reached 1,100°C. This heat enabled the carbon from the charcoal to diffuse into the iron.
Each cementation cycle, or 'heat', took three weeks, producing about 10 tons of steel. The firing took 6 - 10 days and the furnace was then allowed to cool for a week, before the bars could be extracted.
Forging the steel
These bars of 'blister steel' were taken to the nearby water-powered forge, to be made into items such as cutting tools and springs. The steel had remarkable flexibility and strength, and was said to be of excellent quality.
The Derwent valley was the centre of the British steel industry in the early 18th century, as it had all the natural resources needed for the cementation process. It had plentiful supplies of charcoal, coal, clay and sandstone, and easy access to the North Sea for the import of Swedish iron.
Derwentcote furnace went out of use by 1891 and subsequently fell into disrepair. It was restored by English Heritage in 1990.
Cranstone, D 1992. 'Derwentcote Steel Furnace', London: English Heritage
Cranstone, D 1997. 'Derwentcote Steel Furnace: An Industrial Monument in County Durham', Lancaster: Lancaster University Archaeological Unit, Lancaster Imprints 6
The text and pictures on this page are derived from the 'Heritage Unlocked' series of guidebooks published in 2004. We intend to review, update and enhance the content in the near future as part of the Portico project, whose objective is to provide information on the history, significance, research background and sources for all English Heritage properties.