# Common mistakes in cupellation



## Dr. Poe (Nov 21, 2011)

I think I want to help with some common mistakes made by newbies.
This first post shall be about cuppellation mistakes: Cracked cupels and glassy beads.
Wither one uses bone ash or magnesite cupels in assaying, there are a few things that should be done. Store your cupels in talcum powder. This keeps them bone dry and so prevents the cracking that occurs when even the slightest humidity is absorbed. This is a good idea even in the arid desert. Rub some of the talcum into the center bowl of the cupel. This prevents the absorption of minute crystals. Molten litharge or oxide of bismuth will absorb and pass through the talc into the cupel. Cupellation should not be done by placing the prill into the cupel while cold and then placing it into the kiln. It's better to place the cupel in first without the prill, heat it half way, then use tongs to quickly add the prill to the cupel. Of course the prill must be completely dry. Bring the temperature up all the way before opening the oxidizing vent. The temperature of molten litharge is lower than the melting points of most precious metals except silver. Raising the 
temperature prior to allowing oxidation allows precious metal particles to unite. If using lead or bismuth don't breath those smoky fumes. If you do, you are looking at anemia, bone loss, mental problems and even the possibility of leukemia.
If the product (button or bead) of your cuppelation is alloyed with much ruthenium, it will be brittle, non-maleable, may shatter or crush with a hammer. Even if the product is gold. The density will seem too low. Under the microscope, the sponge holes can be seen. Often the appearance will be like a golden shine on a glassy appearance. Ruthenium, rhodium, iridium, osmium, tellurium, selenium, and antimony can also change you bead. Rhodium hates gold and so forms swirls in the button. Iridium makes a rainbow under the bead. Osmium, tellurium, ruthenium, selenium and antimony can ruin your beads by making them so brittle one mistakes them for glass. One last thing to close this post; Unless the lead is guaranteed as "silver free", expect some silver will be in your bead or button. 
I should add that scented baby powder (talcum not cornstarch) is what I use. Dr. Poe


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## 4metals (Nov 22, 2011)

I will admit most of my assay experience comes from high grade alloys or low grade sweeps from jewelry manufacture but lately I have seen a few beads which seem to shatter like glass. 

I have had a black powdery residue contaminate the parted gold when ruthenium (from Pt Ru alloy) is present in small quantities in the bead. In the case I just described the resultant bead is not like glass but the silver added is always 3X the sample weight.


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## duncan (Jul 27, 2012)

Where I work we pre heat cupels for about 5-10 minutes in the furnace. We pull them out and let them cool.

Since we cupel 84 samples at a time, it is impractical to load the lead buttons in to the cupels while they are in the furnace. We place the buttons into the pre heated cupels then load that to the furnace.

Once our Mag-oxide cupels are pre heated, they turn from a grey color to a brilliant white.

De-slagging was mentioned and is also very imprtant. Not only does deslagging make the dore bead (or prill) easy to remove from the cupel, it also prevents slag buildup inside the muffle. Right before a furnace relining I have seen slag drip from the ceiling into the cupel and make removing the prill almost impossible.


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