Unless I misunderstood him it sounds like PGMs cause it to freeze early no matter what you do outside of adding extra silver first.
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No matter what it is, one need to "babysit" it at this stage.
Have you read Bugbee?
Yes, an according to him if lead is retained the bottom of the bead will be smooth. Mine was definitely not and had to be picked from the cupel.
If it was lead or silver, what’s this leftover metal I have that wasn’t dissolved by nitric? It doesn’t look like gold.
I babysat it.
Martijn
Well-known member
As the lead oxidizes away, the combined melting point of the button rizes. Once this melting pount comes above your furnace temperature, it solidifies.
Edited to say: and the lead leftbin the button can no longer oxidize.
The lead oxide still present on the surface can no longer flow off a molten surface and will stay on the button.
Keeping it in longer would have evaporated the litharge, I think.
But adding silver to the cupel is the solution to getting all lead out.
https://www.americanelements.com/meltingpoint.html
Martijn
Well-known member
Melting points of metals:
Platinum: 1768.3°C3214.9°F
Lead327.46°C621.43°F
Palladium1554.9°C2830.82°F
Silver961.78°C1763.2°F
Lead-Platinum Alloy290 °C554 °F
Silver-Lead Alloy304 °C579 °F
Silver-Palladium Alloy651 °C1204 °F
This makes cupelling PGM's so much easier.
Platinum: 1768.3°C3214.9°F
Lead327.46°C621.43°F
Palladium1554.9°C2830.82°F
Silver961.78°C1763.2°F
Lead-Platinum Alloy290 °C554 °F
Silver-Lead Alloy304 °C579 °F
Silver-Palladium Alloy651 °C1204 °F
This makes cupelling PGM's so much easier.
So I did another one with different material and had the same issue.
Within 20-30 minutes my 30g lead prill is almost completely gone with only the tiniest speck inside. I can see it actively driving during until it reaches this size.
I leave it in another 10-15 minutes and it doesn't shrink at all and appears to be doing nothing. Its not freezing, my temp is 900-950c.
I have no idea what's going on. It's like it's getting stuck at 99% completion.
Any advice what I can try to fix this? Just leave it in for over an hour even though after 20-30 minutes it's 99% finished?
Martijn
Well-known member
So your furnace has 900 to 950 temperature, which is too low to melt silver @ 961 C, Pgm's are much higher.
That means before all the last bits of lead are out (traces), your button freezes, because it is so darn cold in there. > end of cupellation> ugly frozen button.
Did you add silver this time?
If it stays molten and you can see the oxides no longer being driven off, the cupelling is done.
If there was close to nothing left, then that is what was in the material. Precious metals do not evaporate easily, silver does to some extent, but for a half hour @ 950 C, I would say not really noticable.
Cupelling is a part of fire assaying, so it should be precise without pm losses.
Which makes me think you do not have pgm's.
Flashing happens when the last molecule of lead is oxidized from the button and flows in the cupel.
That means before all the last bits of lead are out (traces), your button freezes, because it is so darn cold in there. > end of cupellation> ugly frozen button.
Did you add silver this time?
If it stays molten and you can see the oxides no longer being driven off, the cupelling is done.
If there was close to nothing left, then that is what was in the material. Precious metals do not evaporate easily, silver does to some extent, but for a half hour @ 950 C, I would say not really noticable.
Cupelling is a part of fire assaying, so it should be precise without pm losses.
So it stays molten but does not flash? Freezing only happens when it's too cold in the furnace.
Which makes me think you do not have pgm's.
Flashing happens when the last molecule of lead is oxidized from the button and flows in the cupel.
No I didn’t add silver because I don’t think I have PGMs either. And this was a completely different sample from an entirely different claim where the gold is known to have 40-50% silver.
Ron Boykin and all the manuals I have read said 850 then 900 or 950. You’re saying I need to go higher? 975 or 1000 maybe?
I can’t say for certain but I think it was molten. It’s only 0.2” at the end and barely viewable to the eye in the furnace. It was so small. I honestly thought there was absolutely nothing in there while up to temperature so I let it go another 10 to 15 minutes.
It seems like it must not be finished considering they all appear the same size with the same characteristics shown in previous threads. But the confusing part is according to Robs video, the bottom of the bead will be smooth if lead is still present. Mine is firmly fused with the cupel.
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Martijn
Well-known member
No, i think you should follow the instructions. most of the lead will oxidize at 850, and then raise to 950.
You can pick the bead out before it cools and sticks to the cupel.
Read Chapter V of Bugbees book on Fire assaying well and then read again.
It describes in detail what to do and what to look for, including losses and reason for losses.
The book is in PDF form in the forum library.
I’ve read it multiple times and I’m coming up with nothing. Which is why I’m asking for advice on what to try next
This is from page 96/97:
Now go and study.
The minimum temperature at which cupellation will proceed
has been a more or less disputed point, owing largely to a difference
in conception of the process and involved conditions. At
least three methods of measuring the temperature have been
proposed. One experimenter held his pyrometer junction onequarter
inch above the alloy in the cupel, another placed the
junction inside the cupel, while a third measured the temperature
of the alloy itself. According to Fulton* the alloy itself must
be between 800 and 850 C. Litharge melts at 884 (Mostowitch),
906 (Bradford), but passes through a pasty stage before
becoming liquid. It would seem that the cupel itself must be
maintained above the melting point of litharge in order to allow
of absorption. At any event the cupel is much hotter than the
space around it partly because of the heat generated by the oxidation
of the lead and partly because the cupel rests on the floor
of the muffle and its interior portion becomes heated by conduction
through the muffle floor on which it stands. Bradford f
found 906 C. to be the minimum cupel temperature which would
permit of absorption of litharge. Lodge \ found that for silver
cupellation with a moderate draft, the muffle temperature (taken
one-quarter inch above the cupels) should be between 650 and
700 C.
Ok, you have read it multiple times. Good for you. Now, at the very real risk at being perceived as rude, sardonic, and a bit sarcastic, please allow me to elaborate on how I learned to study new material, and what I encourage others to do.
In this case, read Bugbee’s book. Read it again. Second time through you should begin to understand the terminology. Read it a third time, writing notes and questions as you go. Actually recording your thoughts with pen, on real paper, is a remarkably good way to aid formulation of ideas and procedures.
If you are properly following the processes laid out by Bugbee, you should be able to outline a detailed flowchart on assaying. If not, you have more study to do.
I use the same technique in studying new material or learning new processes, regardless of topic.
Time for more coffee.
