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Smelting
Up to the 17th century, smelting was mainly carried out in structures called 'boles' or 'bales'. Smelting at boles
was seasonal as it took advantage of strong prevailing winds. The sitting of boles was a compromise between the
availability of fuel and ore, and the need for an exposed, preferably southwest facing site with sufficient draught.
There has been little archaeological investigation of boles so we are uncertain of how they worked - however they seem
to have been little more than a bonfire. The slag from boles was still very rich in lead and was often taken away for
re-smelting at a small hearth known as a 'black work oven' which probably operated at a higher temperature and used
bellows.
Improvements in technology led to small permanent smelting mills being constructed with fixed ore-hearths and
foot-powered bellows. These early ore-hearth mills also used wood for fuel, and this was sometimes dried in a kiln
called a 'chop wood kiln' or 'white coal kiln'. These wood drying kilns look like small lime kilns and can sometimes be
found dispersed through wood in lead mining districts.
Smelt mills were built in places where several tracks met, as the dressed ore continued to be transported from the
mines in the panniers of pack-animals. After about 1700 a method of smelting at ore-hearths using a combination of
peat and poor quality coal had been developed. This meant that the smeltmills could be sited nearer the mines as they
were no longer dependent on wood for fuel.
There were two types of hearths found in smelting mills. The cupola or reverberatory furnace was more sophisticated
and more efficient, but as it required good quality coal it was not popular in the upland northern dales, where peat
was more readily available. Here the ore-hearth continued to be used, with
water-powered bellows providing a steady blast of air to heat up the furnace. The smelting mills usually had two chambers, one with the hearths, the other
with the waterwheel and bellows. Molten lead ran from the hearths, and was ladled into a pig mould.
The fumes from the smelting process were highly poisonous, as the smoke contained vaporized lead, sulphur dioxide
and arsenic. To condense the fumes, long horizontal flues were built leading to chimneys on distant hill top sites.
Some lead could be recovered from the flue, but the work was extremely unpleasant even by comparison with other
dangerous work in lead mining.
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