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Cupellation for Removal of Silicates
Equipment and supplies required
- Cupels (approximately 4" in diameter)
- Stirring rod
- Equipment to melt the lead
- Soldering block or brick
- Electric burnout furnace or similar kiln (1650° F. required).
- good ventilation
- Preheat your burnout furnace at 1650° degrees Fahrenheit for 1 hour. Place a soldering block underneath the cupel. If lead should happen to spill out of the cupel at some time, the soldering block will be there to protect the bottom of your furnace.
- While the oven is preheating, melt 3-4 weights of lead for every weight of material you want to cupelate. A 3.5" cupel will accommodate approximately 1 pound of material total weight. Add the material to cupelate to the molten lead. Stir. It is best to alloy the material with the lead but mixing is all that is required.
- Pour the mixture into a round mold and allow it time to solidify. Place the ingot in the cupel and place the cupel in the oven. Alternatively, you can pour the lead mixture directly into the cupel and then place the cupel in the oven. Put a soldering block under the cupel to catch any lead that may spill so that it does not make a hole in the bottom of your oven.
- Within approximately 2 hours, the cupel will absorb everything except the precious metals, leaving a solid button of gold and silver. Do not remove the cupel from the oven nor lower the temperature until all the dross has been absorbed and the button has solidified.