Firstly, edge rollers only seem to have had a very limited application for crushing lead ore. Stamps were even less likely to feature, though they were used for crushing glassy slags. Stamps were sometimes used alongside roller crushers for crushing the chats returned from the hotching tubs.
Secondly, Peter is right, the importance of a uniform sized feed for the efficient opperation of each stage in the dressing process cannot be overstressed.
The dressing process and its mechanisation has interested me for a long time - being one of the few areas of non-ferrous metal mining to see the sustained introduction of major, inter-related innovations. I long since concluded that there is no easy answer to the point made by Peter C.
Pre-19th century mine owners obviously saw brangled veins as a potential source of ore, but were constrained by the cost of mining and dressing each bing (in other words the 'unit cost'). Many factors must have contributed to create a demand for mechanised dressing (not just crushing) and to make it possible for it to succeed. These factors include (in no particular order):-
Organisational changes which allowed for the consolidation of smaller mines into better capitalised ventures, covering bigger areas. This process varied by area. In the North Pennines, for example, large companies (London Lead Co. and the W.B. Mines) were active from the late C17th. In other parts of the country, small mines predominated until much later. Even where mines covered large areas, it is not always clear that they were organised (or even perceived) as anything other than a group of small workings.
The introduction/wider use of railways in the later 18th century allowed more vein-stuff to be moved underground more cheaply/easily.
Greater centralisation of these larger mines - made possible by horse levels, whim shafts, railways etc.
A more systematic approach to prospecting for, developing and working new veins. Particularly changes in the way miners worked. Mechanised dressing allowed them to remove larger parts of the vein as opposed to picking out the richest parts.
A general reduction in the 'real' price of lead (not sure about copper, tin etc) over time. Hence an increasing need to maximise the percentage of ore recovered.
Mike
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