The minimum temperature allowable during the driving depends also upon the type of cupel-cs ceramic

The minimum temperature allowable during the driving depends also upon the type of cupel used and the size of the button and bead. Large buttons that are cupeled rapidly in bone-ash cupels with the ordinary shallow cup frequently permit minimum muffle temperatures as low as 790¡ãC and will finish at 820¡ãC if the beads are small.
Magnesia cupels under similar conditions require minima of 830¡ãC in the driving trough, and 840¡ã to 850¡ãC to finish.
The formation of feathers of litharge can be observed readily with bone-ash or bone-ash-cement cupels and serves to indicate proper driving temperature, but when copious feathers form on magnesia cupels the temperature is dangerously near the freezing point.
Finishing temperatures greatly in excess of 900¡ãC, as measured in the manner indicated above, should be avoided in all cases, as higher temperatures cause greatly increased losses of gold and silver with all types of cupels and all variations in button and bead weight.

magnesium oxide and bone ash cupels	magnesium oxide and bone ash cupels	Magnesium sand cupel	Ceramic Couple
Plate cupel	Fire assay cupel	magnesia boat crucible	magnesium oxide crucible

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