home made cupels

Advertise with us
Shop deals on ebay
shop deals on amazon
xelexo
Gold Refining Forum

Help Support Gold Refining Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
I buy my cupels from Charles Butler in Bodfish california

he has a web site - - you can Google it. I don't remember the cost.
His torch assay video shows him making some; although I am pretty sure that he buys already made of late.
He does have recipes & instructions if you want to make your own.
 
when not wanting to use up my good cupels I use sheetrock, cut two squares about 4 inchs. make dimple shape in one, sit it on other, can melt gold, copper, or silver on this with acytelene torch, sheetrock melts but at much higher tempeature than gold, after melt, can just push out melted portian grind an wash in water to get bead of metal if small bead, or pan it, I usually use this with flux of crushed glass,sodium carbonate (washing soda), flour,ect... sometimes lead litharge if assay, -----or just borax if just melting. this is not for fine gold or silver, i use my store bought cupels for that. ------- another trick cat litter clay makes a good refactory clay fer yer homade furnace when in a bind.
 
butcher said:
i use my store bought cupels for that. ------- another trick cat litter clay makes a good refactory clay fer yer homade furnace when in a bind.
Click to expand...
You might consider buying small clay melting dishes from a jewelry supply house in place of using cupels. Unless you're cupelling, I see no need to use them. Melting dishes have a considerable life span if you anneal and season them properly when new. You can expect months of service if you use them only occasionally. On a daily use basis, they last for weeks. There used to be a light brown clay dish available, which was not known for longevity. The ones made in white clay, sold under the Vigor name, will perform very well.

Harold
 
Hi Harold:

Just finished reading your post on, “substitutes for cupels”. I just purchased some new three inch melting dishes from Steve and would appreciate your advice on how to anneal and season them properly before I start using them.

I want to use these melting dishes for melting refined silver. I have dissolved several hundred grams of .925 and sterling jewelry in nitric and cemented it out with copper. I now want to melt some of the cemented silver into two ounce ingots to be used as an anode for a small silver cell that I am trying to build. I will be using my Argon electric furnace.

Any advice you could give me would be greatly appreciated.

Thanks in advance.

Tom
 
Tom,

Good to see you on the board.

My experience goes hand in hand with what I've read about the typical clay dish. They are quite stable if you heat them slowly at first, raising the temperature slow enough that entrapped moisture can evaporate. That prevents cracking. I used to place a new dish on a low flame on my hot plate and let is sit for maybe 15 minutes. I would then place it on a rest (block of asbestos in my case) and heat it with a rosebud, slowly, running the torch in circles around the dish. When the entire dish was up to a low red heat, I would then sprinkle borax on the dish and melt it with the torch. A thin film is all that is desired, otherwise when you pour off the values, flux goes with the metal. You'll come to realize how much is required the first time you use the procedure.

If you use your melting dish only on occasion, I suggest you always heat it slowly before putting it in service. They have a way of absorbing moisture when not in use----and are subject to cracking, much the same as a new one. That's pretty much the same procedure that is advised for graphite/clay crucibles.

Considering you'll be melting silver that has been recovered with copper, you'll get some copper oxide in the flux. That will make it get thicker and thicker each time you use the dish. The process of cleaning the dish using soda ash can be applied to rejuvenate the dish, although at a slight loss to dish thickness. Before cleaning is necessary, you can usually add more borax to the dish to keep it in operating condition. The flux coating not only absorbs some of the oxides, but also lubricates the molten metal so it pours well. When some starts sticking to the lip of the dish, it's time to refresh the coating.

I suggest you use borax glass, or anhydrous borax. It melts without all the frothing and blowing about that you get with the light, fluffy borax that is commonly available. Both do an adequate job, however, so it's just a matter of convenience. It isn't easy to find, and is not cheap, but it's worth the effort if you can find some.

Good luck! Running a silver cell is lots of fun. Make sure you have an adequate filter bag, so the slimes can't mix with the recovered silver. If you've used any of the silver for inquartation and have processed any dental gold, could be you'll recover some platinum and/or palladium.

Harold
 
Tom,

I have a video on my website that demonstrates the preparation of the dishes as per Harold's instruction. It's in the melting section of the videos.

Steve
 
I suggest you use borax glass, or anhydrous borax. It melts without all the frothing and blowing about that you get with the light, fluffy borax that is commonly available. Both do an adequate job, however, so it's just a matter of convenience. It isn't easy to find, and is not cheap, but it's worth the effort if you can find some.


Harold, Anhydrous borax is not too expensive and can be found at pottery supply house in 1- to 50 lbs. Let me know where anyone is and I will try to find a co close by. Wyndham
 
You can also make anhydrous borax just by heating the hydrated salt. Make a lot at a time, grind it up when cool in a mortar and pestle and save it in a tight bottle.


Lou
 
I have experimented with homemade cupels using bone ash moistened with a mixture of 1 TBS glue, 2 TBS sugar, and 1 cup water like Charles Butler teaches. I also replaced the bone ash with sifted wood ashes from the house heating furnace with some luck. It seems to work but sometimes gets pits that seems to shield the lead button from oxidizing completely and Mr. Butler told me that it could contain some gold that would give false assay results but for my learning experiments it is much cheaper than bone ash.
Anyone else try some substitutes for bone ash?
 
Sorry about a second post but I couldn't seem to get to the bottom of my last post to add more.
I just got a bag of mortar mix (cement only, no sand or gravel). I used a cupel mold bought from Charles Butler of ButlerLabs to press out some tiny cupels for torch assaying and tested them out. They really should have been dried first but I was just testing them out so I torch dried them and added a small lead bead from some action mining flux and some crushed ore known to contain gold. The lead oxide didn't soak in as well as a real bone ash or magnesite cupel but it may have been because of not being fully dry or maybe I used too much oxygen in the torch flame but it did result in a small gold bead.

I also tried using a larger cement crucible made months ago to assay this sample and it worked o.k. I don't know if I would want to risk a large amount of gold with this homemade stuff but it worked for my testing and it was a lot cheaper than store bought ones.

It seems like a waste to spend a dollar or more for a cupel to get a penny or less of gold but for a real assay it may be worth it. For doing quick tests for yourself, this works for me.
 
Mortar mix already has sand in it. You must find plain Portland cement. It will be marked as such. It is the binder in concrete and mortar mix. I bought an 80# bag several years ago at Home Depot for about $6. I am still working from that bag. Controlling the moisture to make these is vital to prevent splitting.
I have also used straight Vigoro brand bone meal from the garden center. These work in smaller sizes just pressed with no additives and then roasted to ash to drive off the fats present. These will smell bad a lot like burning hair. Roasting after pressing reveals the ones that will split in use. They soak lead like nobodies business but are limited to about 1"diameter or less. Larger sizes will need a binder of some sort.
 
Yes, you are right about the sand. I got the mortar mix for free since the bag was ripped and spilled. That would explain the glassy look when I tried cupelling a small test.

I got some store bought (action mining) cupels and tried one out with the torch. One problem I am having is silver. I want the nice gold color in my tiny beads but after trying a larger sample I think I have silver since there was a considerable amount of "sprouting" on my last attempt. Either my lead I used was contaminated with silver or my melting cup (made from cement a year or so ago) is contaminating my tests with silver from previous tests (likely).

I did try the straight bone MEAL and it did work but smelled bad and again a tiny silver colored bead. I have no nitric acid and won't pay the hazardous shipping fee to get some so I have no way that I know of to part the beads. They are mostly almost microscopic except for the last one. I've been saving all my tiny cupels to someday recover the precious metals and hopefully even the lead. I've tested the lead oxide layer in some with a reducing flame and can get the lead to reform into metal form again. I don't want to just throw them away since they contain some gold/silver/etc. and I figure the lead oxide is probably more dangerous than the lead metal. No since contaminating the Earth any more than I have to. The lead does form some really pretty colors on the sides of the cupels. I can see why it was/is used in paints.

Thanks for the great forum full of great knowledge and great people. Keep it up everyone.
 
The text I have on the subject is: "A Manual Of Fire Assaying by Charles Herman Fulton". This was a college text from Penn State back in 1911. The older texts have much more info on making your own stuff, from furnace construction for several types of fuel, to making cupels, and formulating your own fluxes. The commercial made cupels are likely more reliable for accurate scientific assaying, but for experimenting with the process home made will work fine. This book is well worth looking for. You may be able to find it at your local library.
 
Here is a link to that book;

http://www.archive.org/details/manualoffireassa00fultiala

There are also alot of the older books on the site.

Jim
 
Thanks for the link to the book and the link to e-bay nitric acid. The nitric was expensive but the shipping was WAY less than other places I checked. Probably won't be buying any but it's nice to know it is there. As for the book, I have it downloading now. This forum is full of great people!!!

Back to the homemade cupels and my silver problem: I still think I have silver but not as much as I thought. My lead "sprouted" as it cooled down when I moved the torch away before the process was done. I thought only pure silver would do this but I seem to be wrong (Admitting it is the first step to a solution) My real problem is I'm just working with too small amounts of precious metals. With a magnifying glass and good light I can find TINY beads in the cupels, both the homemade and the store bought ones so I just have to back up and start over. The process does work and it don't make gold where there is none. I'm probably the only one on the forum that tried to get to the end product too quick.

Thanks again everyone for making this kind of information available for little more than the cost of time to read and study.
 
If your flux is balanced and your assay is going correctly your PM will be quite pure, nearly round and sitting just barely touching the cupel, it will be attached but not strongly. Almost like a bb in a teacup. If your bead of metal is flat and firmly bonded to the cupel it is a sign that you havent removed all the base metals.
 
I guess I should have ordered it when I saw it (E-bay nitric) I can't find it again either and I don't even see the message I got the item number from.

Maybe I made it up or maybe I've been breathing too many lead fumes :?

It was from a company that also sold biodiesel making supplies. Maybe if somebody really posted then deleted the message they can jump back in with more info. I think the listing was ended but there was other auctions or buy it now sales (I thought)
 
I looked at the nitric acid auctions when the subject first came up. Now they don't even show on the completed side (and it has not been that long ago) which tells me the auctions were scrubbed by eBay perhaps by governmental request.

Shades of big brother.

Without a buisness that requires it, You'll have to make what you need. Till they put a stop to that as well.
 

Latest posts

Back
Top