The lead mining industry in Derbyshire declined in the late 18th century. However the discovery of other minerals found within the land, and spoil heaps from earlier miners, provided a new lease of life for Stoney Middleton Dale.
Stoney Middleton Dale (across the road from Castle Rock) is the former site of the Paint Mill and latterly Rock Mill. It was powered by a waterwheel and processed barytes, which came from a local site now
known as Cavendish Mill. There the galena (lead ore) and fluorspar were separated from the barytes. The lead went to Darley Dale and the fluorspar to Sheffield.
The barytes was dried over a fire on steel sheets before it was cooled and fed by conveyor to large millstones. Here it was crushed to a fine powder, before being bagged and taken to Liverpool for distribution all over the world for various industrial processes, specifically the production of paint.