Derbyshire lead mining history: Encyclopedia II - Derbyshire lead mining history - Technical change

Derbyshire lead mining history - Technical change

After a mid-sixteenth century slump the industry recovered, new mines were opened on Middleton Moor, and production increased, a recovery mainly due to technical developments. While traditional extraction methods had persisted there were vital changes in the ways in which ore was prepared for smelting and in the smelting process itself. The traditional smelter was a bole, a large fire built on a hill and relying on wind power. It functioned best with large pieces of rich ore known as bing and could not deal with anything small enough to pass through a half-inch mesh riddle. The bole smelter therefore resulted in large amounts of ore accumulating on waste heaps. It required two days of strong wind and could only function when the conditions were favourable. In the late sixteenth century wind power was abandoned and the smelting blast was provided by a bellows driven first by foot, to an ore hearth, and later by water-power in a smelting mill. The mills were fuelled by “white coal”, which was in fact kiln-dried branch wood. Wood was preferred to charcoal for the main furnace, which smelted ore from the mines, as charcoal generated more heat than this furnace required. Drying the wood eliminated smoke, which would have made it difficult for the smelters to keep the necessary close observation of the process. Charcoal was used in a second furnace, which resmelted the slag from the first, and required greater heat. Draught for the furnaces came from two large bellows driven by the water wheels. Lead ore of all grades was first broken or ground again into finer particles and rewashed to produce very pure ore for the furnace. These smelters could deal with much finer particles of ore and new techniques were introduced to provide them.

Before a miner could sell his ore he had to dress it. Dressing was the process of extracting the ore from the rock in which it was embedded and washing it - a further refining process. In the days of bole smelting the ore was roughly washed clean of waste minerals and dirt before being riddled for bing ore. The ore for the new smelters was smashed, or crushed, into pieces about the size of peas. This was done by hand, using a hammer called a bucker or, in larger mines, on a crushing circle, where a horse dragged a roller round a paved circle on which the ore was placed. Crushed ore was washed either by running water over it in a sloping trough called a buddle or by placing it in a sieve fine enough to prevent any ore particles passing through. The sieve was then plunged several times into a trough. In each case the object was to allow the heavier, lead-rich, particles to sink, enabling those containing lighter, unwanted minerals to be skimmed off the top and removed. These processes were then repeated at the smelter. By the seventeenth century new mines were being opened, shafts driven deeper, and old waste heaps were yielding new supplies for the smelters.

Adapted from the Wikipedia article "Technical change", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki