How did it work?


Metallic iron combines readily with other elements to form compounds such as iron oxides. Thus the metal does not occur naturally but some of its compounds, termed ores, are plentiful.  To release the metal, ore and charcoal were fed into furnaces where they burnt at high temperature due to the air blast provided by the water powered bellows.


Michael Blackmore’s drawn reconstruction of a furnace, near Gilwern, shows a furnace built into a hillside with a charcoal store at top level. Water is fed from the left to a water wheel beneath the narrow sloping roof.  It powers the twin bellows. The cast house, where the molten iron solidifies, is on the lower right hand side.


At Gunns Mill the placing of the three units is different:  the cast house is where the drawing above places the bellows.  The latter are round the corner against the left hand face of the furnace. Further left are the water supply and wheel pit lying parallel with and against the bank.



In the furnace heat and chemical reaction combine to produce liquid iron which pools at the bottom of the furnace.  From there both iron and slag (the molten rocky waste) were tapped , i.e. run out, to cool and solidify.  The iron flowed onto a sand bed containing main and side channels where it formed ‘sow’ and ‘pigs’ of cast iron. It could also be poured into moulds to produce articles such as fire backs and cannons. The slag was discarded. 

Image Copyright Brenda Blackmore


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