The History & Archaeology of Cadia Valley


Copper Mining

Lentin’s description of copper smelting in Anglesey in 1800

Lentin in 1800 described the copper smelting processes in use in Anglesey, North Wales. The process is summarised below.

1. Roasting. The first process was the roasting of the ores, whereby the sulphur would be separated from the ore, either to allow the sulphur to go to waste, as in heap roasting, or by using specially constructed roasting kilns or conical furnaces. These processes were described by Matthew Boulton in 1787, Bingley in 1798, Lentin in 1800 and Faraday in 1819 at the mines in Anglesey in North Wales.

2. Calcining. The second process involved taking the partially roasted ores and placing them in a calcining furnace, to further remove the sulphur content of the ores.

3. Smelting. The third process consisted of the smelting of the ore with fluxes, as appropriate. The ore was frequently smelted with slag derived from previous operations. The smelting process removes any remaining sulphur, melts the metal and slag into a fluid state, so that it may be drawn off at the tap hole into a sand filled frame, where the metal (matte or regulus) and slag solidifies into the shapes cut into the sand.

4. Smelting. Once the product has cooled in the sand frame, it is broken up and the matte or regulus is separated from the slag. The matte is then again smelted in the fourth process. Any slag is skimmed off and the remaining metal is led out through the tap hole into a water container, which causes the metal to separate out into small granules, the process being called granulation. The purpose of the fourth process is again to remove remaining sulphur, while the granulation of the metal provides a greater surface area to remove further sulphur in the next process.

5. Calcining. The granulated metal is placed in a calcining furnace and heated without melting in this fifth process to remove further sulphur.

6. Smelting. The product is then placed in a smelting furnace in the sixth process. The floor of this furnace slopes to the front and would be described by Ure as a refining furnace. The slag is skimmed off and the metal ladled out into boxes, so that thin sheets of laminated copper are produced, about 1/4 inch thick. The metal is now in the state of a very impure black copper, which cannot be broken. The thin sheets provide a large surface area for the volatilisation of any remaining impurities.

7. Smelting. The cakes of black copper are placed in another similar furnace and slowly brought to a melting temperature. The metal simmers for a number of hours to allow the calcined parts to scorify. The slag is skimmed off and the copper ladled into boxes as before. This produced what was known as “Blister copper”.

8. Refining. The final refinement of the copper cakes is again achieved in a refining furnace with the addition of a quantity of lead. The slag is progressively skimmed off to allow the calcination of the copper being scorified. The fluid mass is then sprinkled with coal dust and subjected to the process of poling, whereby green wood branches are forced into the fluid, which causes a violent bubbling, thereby purifying the copper. Further coal dust is thrown onto the fluid copper and bubbling continues. Once this process is complete the copper is either made into cakes, granulated into feather-shot or poured out into small bars or ingots.

In 1847, O. Jones of Beaumaris also described the smelting processes at Anglesey. Following on from roasting, he listed the process undertaken:

  1. The ores are calcined.
  2. The calcined ore is melted.
  3. The metallic mixture from process 2 is calcined.
  4. The calcined coarse metal is melted.
  5. The material from process 4 is calcined.
  6. The metal calcined in process 5 is melted.
  7. The copper from process 5 is roasted.
  8. The coarse or blister copper is refined.

Jones also indicated that the ores needed fluxes for successful smelting and for this purpose ores were obtained from other mines.