# Cupelling help



## ben2363 (Sep 2, 2022)

Hi all very new to all this.
I tried my first go a cupelling, and it did nothing at all. 
It started to melt but after 40mins it didnt do a thing. I had furnace at around 950 to 1050.

One thing I didnt do was pre heat the cupels
Is this a must? And for how long if it needs to be done.

Ben


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## 4metals (Sep 2, 2022)

You are a bit sparse with the details. 


ben2363 said:


> I had furnace at around 950 to 1050.


Was that ºF or ºC?
What were you cupelling? Was this a fire assay? What was your lead to sample ratio? Yes, cupels should be pre-heated, it expels moisture and prevents the molten lead pool from spitting.


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## ben2363 (Sep 2, 2022)

°C.
I smelter down gold/silver cons. The sample was full of gelena so I didnt add and lead to it.

300grams of cons.
900 g of soda
300 silica
200 borax
And a iron rod.

After the pour I had a 118gram button

I cut button up and placed in to 4, 7a cupels.

Had in furnace for about 45min and nothing at all

Ben


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## 4metals (Sep 2, 2022)

It’s hard to say how much of the lead sulfide you reduced in your smelt with iron. A #7a cupel only holds about 40 grams which is why, I suppose, you broke the the 118 gram button into 4 pieces. 

I would carefully weigh a few grams, 2 maximum, and wrap the sample in 10 times it’s weight of lead and cupel it normally. The resulting bead will be all Precious metal. From this test you will know the percentage of PM’s in your sample. From there you can adjust the sample to lead ratio until you get the best recovery.


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## ben2363 (Sep 2, 2022)

Thank you. So rule of thumb is 10x the weight??
2 you grams on sample then 20grams lead??


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## 4metals (Sep 2, 2022)

That is just a starting point. Are the cons high in Silver? If so you can likely part the resulting bead in diluted nitric acid to determine the gold content. If the gold is more concentrated than the Silver you will need to add Silver before cupelling to be able to determine the gold by parting.


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## ben2363 (Sep 2, 2022)

Thanks heap. Silver content is low, gold is the higher out of them both.


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## ben2363 (Sep 3, 2022)

Not sure what's going on here.
I put 2grams of the lead/con button with 30 grams lead.

Both were in for 1 hr and 45mins at 950 °C

Any one have any ideas?

Thanks


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## snoman701 (Sep 3, 2022)

One (or more) of a few things:
Too much metal for your cupel. 
Cupel wasn't hot enough and froze (the second picture does not look like the cupel took up much lead)
Too many base metals, need scorification or more appropriate fusion smelt


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## 4metals (Sep 3, 2022)

Was the sample wrapped in lead or just placed on top of it? A 7a cupel should hold the 30 grams of lead but you would see from the side of the cupel if it has been fully absorbed, which in this case it wasn't. Are you providing airflow in the furnace to drive the lead? 

I would try more heat, like 1050ºC the other option is scorification as snowman suggested.


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## 4metals (Sep 3, 2022)

In case you are not familiar with the scorification process I have attached a PDF which I have written for clients that I teach to fire assay.


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## ben2363 (Sep 3, 2022)

Thanks heap. I dont have any scorifictions dishes I'll have to buy some.

That material is now stuck in the cupels so I'll have to brake it up.

I have air flow going the lead was molten the whole time but it just didnt absorb.

Should I re smelt the 118 grams again adding more soda and start from scratch?


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## 4metals (Sep 3, 2022)

Post a photo of the 118 gram melt you started with.


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## goldshark (Sep 3, 2022)

Is that slag on top of your Lead? I don't know if you know to remove all slag, prior to cupellation. Otherwise the Oxygen cannot get to the lead. I would try reheating what you have, pour into a small preheated conical assay mold, let cool, hammer all slag away, then try cupeling with a fresh hunk o Lead.


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## ben2363 (Sep 3, 2022)

Here's what I started with


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## ben2363 (Sep 3, 2022)

How do you remove the slag?


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## goldshark (Sep 4, 2022)

Take the lead collector metal, and hammer it into a cube. By hammering into a cube, this will eliminate most, if not all of the slag. If there is any visible slag attached to the Lead, it will invariably float to the top of the cupel, disallowing Oxygen to reach the Lead . Even picking off any minicule pieces of slag, will greatly improve the speed of the adsorption Oxygen is necessary to oxidize the Lead, allowing the cupel to adsorb the Lead oxide produced in the reaction of heat and oxygen in the cupellation furnace. The difference in a muffle and cupellation furnace, is the cupellation furnace allows Oxygen in, a muffle furnace is relatively Oxygen free. The old school assay furnaces had a separate chamber for assaying, and another for cupellation. They have several on display throughout Leadville ,Colorado, if you ever get there. It is really neat to see some of these preserved.


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## ben2363 (Sep 4, 2022)

No idea what I'm doing wrong I smelter it all back into a 130 gram button. I added 20grams of lead in the smelt. 

I hammer the button most of it broke off not what lead does.

I picked up 2 3grams bits wrapped in 30 grams lead. Had the cupels in furnace for 15mins at 900
Dropped the samples in. It's been 45min and look to be the same results.


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## ben2363 (Sep 4, 2022)

Same results. Any idea's what in doing this was 3gram sample with 30grams lead.


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## Yggdrasil (Sep 4, 2022)

ben2363 said:


> No idea what I'm doing wrong I smelter it all back into a 130 gram button. I added 20grams of lead in the smelt.
> 
> I hammer the button most of it broke off not what lead does.
> 
> ...


If I’m not mistaken the remperature should be higher, try 1050C
Did you buy ir make the coupel dish.


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## ben2363 (Sep 4, 2022)

Yggdrasil said:


> If I’m not mistaken the remperature should be higher, try 1050C
> Did you buy ir make the coupel dish.


I been running now for 30min at 1100c.
I purchased the 7A cupels.
Bad batch? Is that possible


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## Sundown Resources (Sep 4, 2022)

Just an idea, is there a lot of iron in your cons. Looks like you may have excessive Iron. This happened to me when there was way too much iron in my prill from a smelt and I failed to get the smelt chemistry correct.


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## 4metals (Sep 4, 2022)

Your sample size seems to be creeping upward. This time it was 3 grams to 30 grams of lead. If anything until you can get a successful cupellation you should using progressively smaller samples not larger. 

I think that by using the bits that broke off from the main chunk you may have unintentionally been using slags. I would hammer the cone shaped bar flat and drill a sample from the center after you wire brush off all of the loose bits. To start we want to assure you are starting with a lead/cons sample. 

If you do a scorification as per the instructions that lead cone should be hammered free of slag and brushed off to assure most of the slags have been removed before cupellation. My only experience with scorification has been with copper based bullion not lead sulfide (galena) and it has always produced a clear green slag.


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## ben2363 (Sep 4, 2022)

Sundown Resources said:


> Just an idea, is there a lot of iron in your cons. Looks like you may have excessive Iron. This happened to me when there was way too much iron in my prill from a smelt and I failed to get the smelt chemistry correct.


There could be iron in it how do I fix this???


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## ben2363 (Sep 4, 2022)

4metals said:


> Your sample size seems to be creeping upward. This time it was 3 grams to 30 grams of lead. If anything until you can get a successful cupellation you should using progressively smaller samples not larger.
> 
> I think that by using the bits that broke off from the main chunk you may have unintentionally been using slags. I would hammer the cone shaped bar flat and drill a sample from the center after you wire brush off all of the loose bits. To start we want to assure you are starting with a lead/cons sample.
> 
> If you do a scorification as per the instructions that lead cone should be hammered free of slag and brushed off to assure most of the slags have been removed before cupellation. My only experience with scorification has been with copper based bullion not lead sulfide (galena) and it has always produced a clear green slag.


I'll buy some scarification dishes next week and try that. Thanks heaps


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## ben2363 (Sep 4, 2022)

Guy's how long do it usually take for the cupel to absorb all the lead? 30min,? 1 hour? 2 hour?


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## 4metals (Sep 4, 2022)

For a typical bullion fire assay usually 45 minutes. At that point you can see the precious metal balls sitting in the depression without any lead, which has all been absorbed into the cupel.


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## ben2363 (Sep 4, 2022)

4metals said:


> For a typical bullion fire assay usually 45 minutes. At that point you can see the precious metal balls sitting in the depression without any lead, which has all been absorbed into the cupel.


Thank you


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## goldshark (Sep 4, 2022)

Yggdrasil said:


> If I’m not mistaken the remperature should be higher, try 1050C
> Did you buy ir make the coupel dish.


The temperature should be around 800 - 860 C. max for Au. The black scum on top should start to disappear after a while at around 850 C. I don't know what furnace you are using, but a cupeling furnace is nearly mandatory to get good results. It looks like you are not in the 850 C range for long enough, or too much cold air cooling the cupel. The temperature of the cupel needs to be in the 850 C range, not the temperature of the inside of the furnace. That would need to be higher as Yggdrasil mentioned. Picture of the furnace? Maybe see what Jason uses at Mount Baker Mining. He has a good video on cupeling on youtube. Again, the cupel should not exceed 860 C, or you will start to lose Au/Ag into the cupel. Need to regulate your temperature and minimal air flow into furnace. The bead will flash when it is done.


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## Lino1406 (Sep 5, 2022)

960.8 is the temperature to my knowledge (silver m.p.)


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## Yggdrasil (Sep 5, 2022)

goldshark said:


> The temperature should be around 800 - 860 C. max for Au. The black scum on top should start to disappear after a while at around 850 C. I don't know what furnace you are using, but a cupeling furnace is nearly mandatory to get good results. It looks like you are not in the 850 C range for long enough, or too much cold air cooling the cupel. The temperature of the cupel needs to be in the 850 C range, not the temperature of the inside of the furnace. That would need to be higher as Yggdrasil mentioned. Picture of the furnace? Maybe see what Jason uses at Mount Baker Mining. He has a good video on cupeling on youtube. Again, the cupel should not exceed 860 C, or you will start to lose Au/Ag into the cupel. Need to regulate your temperature and minimal air flow into furnace. The bead will flash when it is done.


I'm no cupelling expert I just shared what I have read other places.
Listen to the experts


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## PeterM (Sep 5, 2022)

ben2363 said:


> Same results. Any idea's what in doing this was 3gram sample with 30grams lead.


Ben2363, download this book: "A Textbook of Fire Assaying" by Edward E. Bugbee. Everything you need to know is in there. https://ia800308.us.archive.org/35/items/textbookoffireas00bugbrich/textbookoffireas00bugbrich.pdf


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## ben2363 (Sep 6, 2022)

goldshark said:


> The temperature should be around 800 - 860 C. max for Au. The black scum on top should start to disappear after a while at around 850 C. I don't know what furnace you are using, but a cupeling furnace is nearly mandatory to get good results. It looks like you are not in the 850 C range for long enough, or too much cold air cooling the cupel. The temperature of the cupel needs to be in the 850 C range, not the temperature of the inside of the furnace. That would need to be higher as Yggdrasil mentioned. Picture of the furnace? Maybe see what Jason uses at Mount Baker Mining. He has a good video on cupeling on youtube. Again, the cupel should not exceed 860 C, or you will start to lose Au/Ag into the cupel. Need to regulate your temperature and minimal air flow into furnace. The bead will flash when it is done.


So no air flow? Iv had the door partially open because I read somewhere you need more air flow


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## Yggdrasil (Sep 6, 2022)

ben2363 said:


> So no air flow? Iv had the door partially open because I read somewhere you need more air flow


You need plenty of air, but not so much that it cools the cupel too much


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## goldshark (Sep 6, 2022)

It is a little touchy, in that you do need Oxygen to react with the Lead, but not so much that it cools the cupel. Read the Text book of fire assaying which Peterm gave a link to. Read it thoroughly at least twice. Pay particular attention to the cupeling section.
Thank you Peterm for adding that link. I lent my copy to a"friend" about 40 years ago, and never got it back.


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## snoman701 (Sep 7, 2022)

easiest way to get the airflow is a couple of holes in the door that can be sealed with kaowool or a carved soft brick plug on an as needed basis


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## 4metals (Sep 7, 2022)

A great affordable kiln for assay and even small melts is made by vcella kilns. Their burnout kilns have vent holes in the door and the top to help provide the oxygen and “drive the lead”. 





__





Vcella Kilns Products






www.vcella-kilns.com





Their kilns are rugged and almost bulletproof. And even if they do fail they are easily rebuilt without much in the way of technical knowhow.


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## goldshark (Sep 9, 2022)

Here are some photos of an old school (100 years + ) commercial assay furnace, located in Leadville, Colorado. Note that the lower muffle lining is gone, but the upper cupeling liner is still intact. This was a coal fired furnace. The walls are over 1' thick. Red hard fired brick on the outside, then fire brick, then another layer of some kind of refractory insulating brick. These were used on a daily basis for firing 100's of assays per day. I bet not many still have one of these around. I wanted to build one, but DFC no longer stocks the muffle linings. Cheers to the old school.


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## Shark (Sep 10, 2022)

That brings back memories. Spent some time in the late 70’s poking around the Cripple Creek and Leadville area. Lots of old history in that area.


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## orvi (Sep 10, 2022)

ben2363 said:


> So no air flow? Iv had the door partially open because I read somewhere you need more air flow


MBMMLLC has perfect videos about pyrometallurgy on youtube. Watch them out, you will visually learn a lot about cupelling and smelting.

If I were you, I will try to take like 10g of lead and do a "blank" cupellation - to elucidate wheather the feed is causing problems, or you just do not have equipment/temps/oxygen right.


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## goldshark (Sep 10, 2022)

A couple of things bother me about Jason's techniques. 1. he doesn't show any base line for wether the ore is basic , or acidic. Other then they are concentrates off his shaker table. Usually a quartz concentrate, since Gold is only associated with quartz. Not too bad showing on pyrite cons assay/smelting 2. he never explains, very well, the reason he uses lead, instead of PbO ( Litharge, assay grade ), wether he is producing a mono, bi, etc., silicate flux. Hire a chemist to explain the difference, in layman's terms A couple more minor grievances, but I will not nit pick too much. He's better then anyone else out there, but then again, I haven't seen any other youtube videos touting our industry. Maybe trade secrets keep is out of the main stream? A shout out to Jason, thanks, fun to learn from you. Also a huge shout out thanks to , is it sreetips, or streetips, seen it both ways. Nothing to complain about with your youtube videos, yet.


orvi said:


> MBMMLLC has perfect videos about pyrometallurgy on youtube. Watch them out, you will visually learn a lot about cupelling and smelting.
> 
> If I were you, I will try to take like 10g of lead and do a "blank" cupellation - to elucidate wheather the feed is causing problems, or you just do not have equipment/temps/oxygen right.


A very good idea.


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## SRM (Sep 11, 2022)

goldshark said:


> Here are some photos of an old school (100 years + ) commercial assay furnace, located in Leadville, Colorado. Note that the lower muffle lining is gone, but the upper cupeling liner is still intact. This was a coal fired furnace. The walls are over 1' thick. Red hard fired brick on the outside, then fire brick, then another layer of some kind of refractory insulating brick. These were used on a daily basis for firing 100's of assays per day. I bet not many still have one of these around. I wanted to build one, but DFC no longer stocks the muffle linings. Cheers to the old school.


Actually, I think most ran on charcoal from the nearby kilns. I spent a few decades there working in mines and even at the mining museum. There are, or were, some remnants of other furnaces scattered around the mining district.


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## goldshark (Sep 11, 2022)

Good point. I wasn't there when they were in operation. Would have loved to see the Arkansas Valley Smelter in operation in it's hay days. Talk about contamination! I don't know if you ever knew W.H. Smith. He did assaying for me back in the 80's. His furnace and office has been preserved very nicely.


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## goldshark (Sep 12, 2022)

PeterM said:


> Ben2363, download this book: "A Textbook of Fire Assaying" by Edward E. Bugbee. Everything you need to know is in there. https://ia800308.us.archive.org/35/items/textbookoffireas00bugbrich/textbookoffireas00bugbrich.pdf


Hey Peterm, can you put the book in the "Books" section of the forum, please. I searched the whole book collection, and only found a minor reference to assaying. Headline the thread with "Text book of Fire Assaying" so it is easy to find. Thanks in advance.


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