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Introduction Ore Processing Fire Assaying

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  1. The collected lead buttons are poured onto the table top. Any now solid glass that may have adhered to the lead button is first hammered away from the button. Then, the buttons are placed in order in a tray to be transferred to cupels waiting in the furnace.The slag is hammered away from the lead button.  
  2. Using tongs, the assayer adds the lead buttons in order to the heated bone ash cupels waiting in the cupellation furnace.The lead button that contains the gold and silver is then melted under oxidizing conditions in a bone ash cupel, a special crucible made of ashes of bone that is particularly absorbant to the lead oxide formed, so the lead (as lead oxide) is absorbed into the cupel or vaporized into the furnace and removed from the gold and silver.
  3. The gold and silver bead that remains in the cupel at the end is cooled and weighed.  
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