Questions about cupellation

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Pirotechnia

Member
Joined
Jul 24, 2011
Messages
8
Hi all,

I am new to this forum. I am very much into old fashion assay, crucible method and scorification but have not very much experience about cupellation. Although I have studied the process in great detail from books, both new and old ones. In this google books is a true treasure, which I strongly recommend (you are probably already well aware about).

First question:

I wonder if anyone of you have heard of a custom of involving multiple cupellations of gold?

I mean, this after the parting phase.

As I have understood it, one will recieve collect 99.5% pure gold after the first parting so I cannot really see any point of doing this. However, I am curious to know if you have heard about it or if there is such a custom at all.

Second question:

I am a bit confused about the proportions of lead / bismuth, some books mention this as being of great importance while others seem to say that it's not important at all! I have for example read that about 10 parts of lead is being used in relation to the gold per se (not counting the addition of inquartation i.e. 3 parts of silver).

Third question:

I have read in "A manual of pratical assay" by John Mitchell, that its possible to make direct cupellation of silver bearing
galena per se or by the addition of 2 parts of lead. Is this something which anyone in here have tried? Or direct (without roasting) cupellation of other minerals as for example pyrites containing gold.

Fourth question:

I read in an old book that one should perform a cupellation assay with such a minor proportions as 11 grains of lead, 2 (or 3) grains of silver and 1 grain of gold. This seem very weard to me, because as far as I am concerned one grain represents only 0.006 gram! Any ideas? I am well aware that the weight systems have changed a lot since the last couple of hundred years and is very different in different nations, but the term "grain" is derived from the latin "granum" and should not be that easy to confuse. Any input is welcome.

Thanks in advance!

/Pirotechnia

P.S. I am about to set up a fire assay lab during this autumn, consider to buy my self a small Cress furnace or a Vcella (6), which seems to be the best alternatives after some research in this forum and in other places.
 
Gold will retain silver from the inquartation process, that is why a good assay is corrected for silver retention. No matter how many times you re-inquart and cupel, the silver retention will remain after parting.

I use pre stamped lead cups for cuupellation, their weight is constant as is the sample weight I use. The cups weigh 15 grams and I weigh out as close too a half gram of sample as possible. I run multiple karat proofs for correction and have never had problems from too much lead.

I have never had the need to cupel galena, but I would likely scorify it first.

I never work in grain quantities.

Cress makes a nice furnace but pricey, Vcella is a very nice kiln and excellent value for the money, plus it is easily rebuilt.
 
Pirotechnia, if you're still here. I hope you don't mind, but I moved this to the assaying section.

My answers would be the same as 4metals, except for the furnace choice (Cress vs Vcella).

The best full-view downloadable old fire assaying books on Google Books I have found are the one by Ernest Smith and the one by Fulton. The ones I have used all my life and prefer, however, are the first two listed on this page - the Bugbee and the Shepard and Dietrich. Excellent prices, BTW.
http://www.lmine.com/mm5/merchant.mvc?Screen=CTGY&Store_Code=LMS&Category_Code=assaying

A couple of days ago, I found a copy of Fulton and Sharwood (3rd edition - 1929) on eBay for $20 and ordered it. It's another excellent book. My copy walked off about 10 years ago. Anything by Beamish is good. I recently found and bought a copy of the Beamish/Van Loon, 520 page, "Recent Advances in the Analytical Chemistry of the Noble Metals" from the UK for about $45, shipped. It was the only one I've ever seen at that very low price and I snapped it up. The other listings I've found for this book ranged from $177-$515.

For directly cupelling bullion, most all of the better books recommend .5 gram samples and 10-15 grams of lead, for the final assay. When running crucible fusions, I try to end up with about a 25-30 gram lead button, but that's a different deal than direct cupellation of the sample.

The cupel composition can make a big difference. The types can vary as to the lead retention and potential losses. All in all, I think bone ash cupels are generally the best, but they are more expensive, less durable - they can break easily if handled roughly or if you don't store them properly in a dry area. Only with bone ash can you get litharge "feathers", a visual guide which can tell you if you're cupelling silver at the right temperature. The composite ones (70% Portland cement + 30% bone ash, I think) from dfcceramics.com are much more durable and I have used them a lot - they seem to be quite accurate but the beads also seem to require a little more careful cleaning to remove stuck on cupel material. I don't really care much for the magnesia ones, probably due to their shape and, since they don't hold heat as well as bone ash - they require a higher cupelling temperature and also they require a higher finishing temperature in order to get rid of all the lead. I prefer cupels with straight sides, as they seem to be easier for me to handle with the tongs and also that they will hold more lead than the tapered ones, for the same diameter cupel.

I have had 2 or 3 fairly big Cress furnaces and one #16 Vcella in my life. If I had a choice of just these two, I would definitely buy another Cress with a door that opened upward, no matter the price difference. It's much, much more comfortable to work around than the Vcella that has a door that opens to the side. Also, to get proper air control for cupellation, you have to drill several holes in the door and the top of the Vcella. With the Cress, you only need about a 1/2" hole in the back for the air outlet (you can simply raise the door a crack for a very uniform air inlet across the whole width of the furnace). The Vcella is a good well-built furnace but I will never own another one. Too hot for me. I like to work around an assay furnace with just gloves, long tongs, and maybe a face shield - you definitely need more than that with a Vcella. However, if Vcella would come out with a furnace that had a raise-able door, I would buy the Vcella. Whatever you get, if you are serious about this, I would spend an extra $600 to get a good electronic controller - much better control than the cheapo ones that come on the standard furnaces (these, you have to keep a fairly constant eye on). I've had 2 complete furnace meltdowns in my life, both the insulating brick and the elements, and it wasn't a pretty sight. They could have been averted with a good controller. To be fair, though, both meltdowns occurred on those crappy little jeweler's burn-out furnaces. However, these meltdowns made me gun-shy, so I always split for a good controller. Also, you get much, much better temperature control with a good controller.

I once used a Johnson #142 gas furnace that I really liked, with a raise-able door. They are quite expensive new but you sometimes can find them cheap used. I saw one recently, somewhere, for about $500, but it needed re-lined, etc. One thing about furnaces is that about anyone can reline them with the proper materials. You should buy a separate muffle (about $1000) for cupellation because they usually only come with a hearthplate. The first time I tried cupelling in one I only had a hearthplate (a flat plate as a floor with the gas flame on both sides). I had a couple of rows of cupels going from left to right. The molten lead in the cupels on the sides near the flames blew out of the cupels from the gas pressure and I ended up with a bunch of deep holes (still containing lead) in the ceramic hearthplate. I then put a hard firebrick, or two, on each side of the hearthplate, to block the flames, and put the cupels in between. This worked fairly well, but I was limited as to the number of samples I could run. A muffle would have been much better.

When I started assaying in the 60s, the large refinery I worked for bought 2 large, brand-new, gas-fired, dedicated DFC assay furnaces. They were, by far, the best furnaces I have ever used. Real workhorses with long-life Carbofrax muffles and furnace furniture. My assayer probably averaged 70-100 samples per day, during the 4 years I was there. Running that many assays is hard work and is very very boring. I just initially trained him, worked out the processes, did the troubleshooting, and ran the assays when he was on vacation or sick. I was always very happy when he got back.

I might mention how I learned to fire assay. The above-mentioned refinery, in L.A., was brand new and I got in there on the ground floor. This was in about 1968. My boss and mentor, the refinery manager, was an old-timer in the gold business, mainly in the S.F. area. He was friends with the owner of a large famous assay office in S.F. that had been there since the gold rush (it was the only one left). It's no longer there and I don't remember the name. He arranged for me to spend a week or two there to learn assaying. The head assayer took me under his wing and gave me a very complete, intense education with all the tips and tricks learned from 100+ years in business. I was a quick study and was assaying full-bore the 2nd day there, mainly bullion, ores, and a few electronic components and I loved it. I couldn't have asked for a better education. I still assay using their methods and have probably run at least 10,000 fire assays in my life.

I've said this several times but, as a refiner, having a fire assay setup has made me more money in my life than any thing else. Of course, usually having an AA has helped also. With fire assay, you always know where you stand. Without it, there is usually doubt. I'm an old-timer that doesn't trust anything with a digital readout, unless I or somebody that I know and trust, both in their honesty and abilities, like Lou or 4metals, does both the calibration and the operation - I've seen too many iffy results and I've witnessed a few shenanigans. With fire assay, I can hold the gold in my hand and that's the way I like it. A truism: He who truly knows his values best always wins in any transaction.

Chris
 
Did you like "Recent Advances in the Analytical Chemistry of the Noble Metals" ?. Is the publishing date a recent one?. Anything "new" in it, like the more accurate balances, ICP, etc ?.
 
HAuCl4 said:
Did you like "Recent Advances in the Analytical Chemistry of the Noble Metals" ?. Is the publishing date a recent one?. Anything "new" in it, like the more accurate balances, ICP, etc ?.
Click to expand...

I doubt it. I think it was published in about 1966 (edited - it was 1972). I haven't received it yet, since it's coming from the UK. I once owned a photocopy of Beamish's 600+ page "Analytical Chemistry of the Noble Metals", (a different book that Van Loon didn't participate in) though, and it was excellent. It was published about the same time. I've looked for a copy of it but have had no luck. I presently own the Beamish/Van Loon "Analysis of Noble Metals - Overview and Selected Methods" - 1977 - 325 pp. It's sort of a summary of some of the stuff in the longer books and I tend to use it quite often.
 
OK. Thanks. If you see any new good stuff, please do keep us posted. I can see the publishing dates for the books go back to the 1970s metal prices boom. Most of the new equipment that exists today wasn't available then.
 
HAuCl4 said:
Most of the new equipment that exists today wasn't available then.
Click to expand...

No offense but, who cares? I know I surely don't. Info on the new stuff can be found elsewhere. I guarantee that you will find a lot of valuable stuff, available only in these older books (as far as I know) that you have never heard of. Beamish was The Man, for quite awhile, and I don't know if anyone of his stature has really picked up where he left off - probably, but I don't know who they are.
 
This post makes me wonder, how much solid information, knowledge and useful tools are we loosing at an alarming rate because we think something is outdated, and that these new thingys replace all of them, if not careful the world will starve to death from lack of knowledge, or go back to the stone ages.
 
goldsilverpro said:
With fire assay, I can hold the gold in my hand and that's the way I like it. A truism: He who truly knows his values best always wins in any transaction.

Chris
Click to expand...

"He who holds the gold makes the rules". The Golden Rule.

:shock: :lol: 8)
 
This post makes me wonder, how much solid information, knowledge and useful tools are we loosing at an alarming rate because we think something is outdated, and that these new thingys replace all of them, if not careful the world will starve to death from lack of knowledge, or go back to the stone ages.
Click to expand...

Once you know the basics and understand the concepts it is amazing how many little subtle hints you can pick up from reading the old texts. Build up a library of the old out of print books whenever possible as it may become a lost art. I really feel that a good fire assay (for gold) will yield the greatest accuracy, the instruments like the ICP do wonders for speed and the low levels of PGM's but can't hold a candle to the classic fire assay when it comes to gold.
 
Yeah 4metals. Nowadays anybody can get some book published. In those old days generally the authors of books were real masters of their craft. They could achieve great things with the minimum of resources at hand. A true art.
 
You may find this interesting about base metal oxides in assaying ore. Base metal oxides can often result in slag bound values (it has been happening to me with with ore off of my claim). Here is what I've learned:
1. If the ore has either cupric or cuprous copper it will demand 1.8:1 and 1.5:1 litharge to convert it to a fusible oxide state. Base metal oxides consume lead oxide as they become fusible. During the first 20 minutes of crucible fusion, the base metal sulfides and sulfates lose their sulfur, either as volatile sulfur trioxide or iron oxide acting as the exchange agent and combining sodium and sulfur. All of the sulfides and sulfates have to be converted to their oxides to be fused into the melt; should any base metals be present in their metalic form, only the outer surface will have oxidized and any native metals will be collected by the lead and contaminate the assay button. Native copper is the greatest single offender and is often found in fire assay buttons.
2. Zinc has a 8:1 ratio.
3. Tin has a 13:1 ratio.
4. Magnetite has a 4:1 ratio.
5. Hematite has a 10:1 ratio.
I have trouble assaying black sands because of the hematite and magnatite that is common in black sands. Here is an example:
Magnetite 29.2 gr (one assay ton) x 40% = 11.6 gr x 4 = 46.4 grams litharge needed.
Hematite 29.2 gms x 20% = 5.84 gr 5.84 gr x 10 = 58.4 grams litharge needed.
Magnetite 46.4 gr plus Hematite 58.4 gr = 104.8 grams of litharge to handle the iron minerals and you still need enough litharge to be reduced to metallic lead to corrode the precious metals and to collect them in the bottom of the fusion so you can re-oxidize the lead in the cuppel and collect them as a bead since the precious metals will not oxidize at cuppelling temperatures. If you do not have enough litharge to handle all of the base metal oxides you can have slag bound values and no bead.
 
When assaying electronic parts, you can't have more than 2g, or a little less, of copper in the sample. Otherwise, upon cupelling, copper will be retained in the bead and you then start over. A bead containing copper will tend to be flatter than normal - with a lot, the bead will be discolored and very flat. A common way around this is to first put the sample, with no flux, in the crucible along with some yellow sulfur and fire it in the furnace. This produces copper sulfide which is fluxable. Then the flux is mixed, added to the crucible, and the sample is fused as normal. I've done it many times and it always seems to work - no blue color in the parting solution.
 
4metals said:
Is there any difference using yellow sulfur between sweeps as pulp and metallic drilling?
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I wouldn't think so. I haven't used it for pulps but I have used it for high copper refiner bar drillings. I've only used it for metallic copper. I never really weighed it out but the amount needed could easily be calculated. It works amazingly well. I think I read about using it in an old assay book. I never tried it for nickel or other problem metals but it might work for those also. I usually used hi-litharge for nickel.
 
goldsilverpro said:
When assaying electronic parts, you can't have more than 2g, or a little less, of copper in the sample. Otherwise, upon cupelling, copper will be retained in the bead and you then start over. A bead containing copper will tend to be flatter than normal - with a lot, the bead will be discolored and very flat. A common way around this is to first put the sample, with no flux, in the crucible along with some yellow sulfur and fire it in the furnace. This produces copper sulfide which is fluxable. Then the flux is mixed, added to the crucible, and the sample is fused as normal. I've done it many times and it always seems to work - no blue color in the parting solution.
Click to expand...

That is really helpful. I'm always trying to counteract the sulfides in pyrites - using iron oxide acting as a exchange agent and combining sodium and sulfur making sure there is enough iron to form sodium sulfate. Could I add copper to pyrites with no flux and achieve the same results?

I really appreciate this forum. I am really green as an assayer and hard rock miner and I have learned alot. Thanks for sharing all your hard work and knowledge.
 
dirtdiggaler said:
That is really helpful. I'm always trying to counteract the sulfides in pyrites - using iron oxide acting as a exchange agent and combining sodium and sulfur making sure there is enough iron to form sodium sulfate. Could I add copper to pyrites with no flux and achieve the same results?

I really appreciate this forum. I am really green as an assayer and hard rock miner and I have learned alot. Thanks for sharing all your hard work and knowledge.
Click to expand...

You now know why the active members of the forum tend to be very protective of the moderators, without their years of hands on experience and extensive knowledge of this subject this forum would not be what it is today.
 

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