# Bone Ash Binder for fireing DIY cupels



## Anonymous (Sep 9, 2009)

Anyone here have the formula for making cupels from bone ash and the binder used to hold everything together before firing. Thanks

gustavus


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## goldsilverpro (Sep 9, 2009)

It was common to make them from just screened bone ash moistened with water. I used to buy "composite" cupels from DFC which contained bone ash and Portland cement. They were stronger than the straight bone ash ones, but they wouldn't produce "feathers" when assaying silver, which is no big deal. If you want to wade through these books, there is quite a bit of info, including the apparatus needed for molding them, some of which looks fairly simple to make.


"cupels" making - Google Search


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## Anonymous (Sep 9, 2009)

Thanks GSP, I will try water, I have a metal lathe so I can make a mold for the cupel, another question how much to compress the putty. I'm not planning on doing any assay work way beyond my skill level. 

Just want something cheap to melt my buttons in.

Best Regards
Gill


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## qst42know (Sep 9, 2009)

You should only need to press them just hard enough that they stay together while molding in the damp stage. Larger cupels need a bit more pressure than smaller sizes. Keep the water to a bare minimum to avoid cracking.

Don't forget to pre fire homemade cupels before you trust them.

Straight Portland cement can also be used. I have several sizes of steel molds but prefer this mold of UHMW.

These are 2" across and are pressed in an arbor press.


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## 4metals (Sep 9, 2009)

Typical bone ash mixture for making cupels

this mix will make about 250 1 1/4 inch diameter by 1 inch high cupels

9000 grams bone ash
1000 grams portland cement
2500 ml of water

When the mixture of ingredients is compressed into a cupel it will show no traces of liquid water.
Dry in areas of low humidity for 2 weeks, 4 weeks in more humid areas.

source; Fire Assaying for Gold & Silver by Sigmund L. Smith


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## goldsilverpro (Sep 10, 2009)

gst,

How much water do you add for a given weight of bone ash or BA/PC or just PC? The depression in the photo seems about twice as deep as all the commercial cupels I've seen. Any reason for that?

According to the stuff I read, it is important to screen the bone ash to help eliminate lumps. Some say to only use a certain screened mesh of bone ash One book recommended kneading the mix to eliminate the lumps. Also, if too little pressure is used, it seems that the cupels can be porous and will absorb some Au and Ag. In one place, I think I read that only 10% water, by weight, was added to the BA. You can also make them from magnesia.


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## qst42know (Sep 10, 2009)

I made the mold myself and never had a commercial cupel to compare it to.  The top rim is a bit thin from being so deep and is somewhat fragile while molding and while fireing. If I were to do it over a shallower depression whould be benificial.

Fulton, mentioned the use of straight Portland cement, and 8% water by weight. I never tried the 50/50 mix of Portland/bone ash mentioned as burning the bone meal I had available is a very smelly operation. :roll:

Page 79









A Manual of Fire Assaying






books.google.com





From my experiments in making PC cupels I never did weigh the materials, but the amount of water is very fussy. Too dry and they would fall apart when molded, too wet and they would crack when drying, or worse when fired. I was adding water with a spray bottle and judged when ready by how the Portland clung to the stir stick.


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## EVO-AU (Dec 1, 2009)

To One and All: Chas. Butler uses ordinary white paste as a binder. His cupels for separating the lead from the pms' are about 3/8" inside dia. Sometime back I posted something from another source. Try using ordinary sheetrock for cupels. Sounded interesting, and darn if it doesn't work. Phill


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## butcher (Dec 2, 2009)

I use sheetrock for dirty melts, to save melting dish's, but the dish's for higher grade material and bone ash for lead cupling.


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## Wyndham (Dec 2, 2009)

BTW you can get synthetic bone ash by the pound at any ceramic/pottery supply house. I have a 50lb bag for less than $70 1LB should run about $2.50
Wyndham


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## shadybear (Dec 2, 2009)

So where can you find or buy these molds?


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## Anonymous (May 13, 2010)

Can you tell me what type of mixer I can use to mix bone ash, portland cement and water to make a cupel


4metals said:


> Typical bone ash mixture for making cupels
> 
> this mix will make about 250 1 1/4 inch diameter by 1 inch high cupels
> 
> ...


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## qst42know (May 13, 2010)

If you are making a large batch check the hardware store for a mortar/grout mixer for an electric drill.


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## Anonymous (May 25, 2010)

I'm looking for a machine that can make bone ash cupel
I hope someone can help me


qst42know said:


> You should only need to press them just hard enough that they stay together while molding in the damp stage. Larger cupels need a bit more pressure than smaller sizes. Keep the water to a bare minimum to avoid cracking.
> 
> Don't forget to pre fire homemade cupels before you trust them.
> 
> ...


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## qst42know (May 25, 2010)

I no longer have access to a lathe but any small shop should have no trouble producing one for you.


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## EVO-AU (Sep 27, 2010)

To one and all:

After months of rehab it is kind of nice to punch a key again. 

Why go to all the fuss of making cupels, when you can buy them very cheaply and in many sizes. Try Legend in Sparks, NV. Very interesting catalogue. 

Phill


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## solar_plasma (Mar 9, 2016)

EVO-AU said:


> To one and all:
> 
> After months of rehab it is kind of nice to punch a key again.
> 
> ...




Those are quite big boxes. Nothing for someone who just need a few to try and learn the process.


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## NobleMetalWorks (Mar 9, 2016)

I use rice starch as an organic binder when making precious metal clays, it burns off, totally clean and if mixed with bone ash I imagine the correct percentage should give you a pure bone ash cupel.

However I only suspect this, and cannot be sure if it will work as I suspect it should.

Scott


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## bmgold2 (Mar 9, 2016)

EVO-AU said:


> To One and All: Chas. Butler uses ordinary white paste as a binder. His cupels for separating the lead from the pms' are about 3/8" inside dia. Sometime back I posted something from another source. Try using ordinary sheetrock for cupels. Sounded interesting, and darn if it doesn't work. Phill



I was just looking at his torch assay book and I found the cupel mold that I bought from him many years ago (before he passed away).

His recipe for cupels uses:

8 tablespoons of BONE ASH
1 teaspoon of WHITE FOUR

This mixture is dampened using a mixture of:

1/2 pint of WATER
1 tablespoon of Elmer's all-purpose white glue
2 tablespoons of WHITE CANE SUGAR

I personally tried many things. Portland cement seemed to be the easiest. I also tried sifted wood ashes in place of the bone ash in the recipe above. That kind of worked but the lead oxides sometimes made pockets into the wood ash cupels that messed up the nice PM bead in the end so it didn't work for the torch assays. I didn't try it but pre-leaching the wood ashes (removing pot ash) might have fixed the problem.


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## bmgold2 (Mar 9, 2016)

shadybear said:


> So where can you find or buy these molds?



Here's a thread here where I posted a drawing for one like Charles Butler used.

http://goldrefiningforum.com/phpBB3/viewtopic.php?f=40&t=19860&p=208152&hilit=cupel#p204661

This makes a very small cupel ... not for melting large amounts of lead or PM but works great for the tiny torch assays.


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## bmgold2 (Mar 13, 2016)

Since this thread came back up, I got my little cupel mold out and leached then dried some wood ashes. I mixed the wood ash 50/50 with Portland cement. I moistened it using the liquid mix from a previous post and quickly make up half a dozen tiny cupels.

They were supposed to be baked (microwaved) to dry them but I wanted to play with one NOW.

I used some ceramic wool to build a miniature furnace around the cupel and carefully dried it using a normal propane torch. Looking around, I found some lead pellets and cut a sliver off of one. 

Melting that lead turned it into a tiny ball maybe 1/2 the diameter of a BB.

I switched to a MAPP gas torch running off a large propane tank and after what seemed a very long time, I got most of that lead soaked into the mini cupel. REMEMBER, these cupels are only 1/2" OD and about the same height. The Butler torch assay used very small amounts 1/20 (one twentieth) of a teaspoon of ore and getting a bead of gold of only 0.005 inches diameter in the end indicated 1.49 troy ounces per ton if only gold was present. Most beads would need parted.

Anyway, this makes me think that maybe this torch assay could be adapted to use a miniature propane fired furnace. Something like a soup can forge. Is this wishful thinking or could it actually work?

Personally, I gave up on the torch assaying. Not because it didn't work. I just think a chemical test would be easier for field testing to get simple YES/NO result. The torch assay would be useful for getting an idea of the amount of gold or other PM's in the good samples brought back to lab or yard. If it could work with a normal propane torch without added oxygen, then it might be possible to do the assays right at the site.

I have tried the tiny portable welding/brazing torches and they cost about a buck a minute to run just for the expensive oxygen so that isn't an option. A soup can furnace sounds like the perfect size for this miniature assay.


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## ashir (Feb 14, 2019)

can not find bone ash in pakistan. may be avail but with diffrent names that no body knows is this bone ash!!! 
a person told me that gelatin is bone ash.
another said dicalcium phosphate is bone ash. what i should buy to use as bone ash to make cupels??


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## butcher (Feb 14, 2019)

Bone ash is made from burnt animal bones.
Portland cement or Magnesium cupels will also absorb PbO


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## Owltech (Feb 14, 2019)

ashir said:


> can not find bone ash in pakistan. may be avail but with diffrent names that no body knows is this bone ash!!!
> a person told me that gelatin is bone ash.
> another said dicalcium phosphate is bone ash. what i should buy to use as bone ash to make cupels??



use plain portland cement instead.


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## ashir (Feb 14, 2019)

magnesium is too much expensive here. but plane portland cenent will work. if anybody know the other name of bone ash used in pakistan then must inform me. and here is no label of portland cement, its just written "cement", but i hope i can find some cement with labled as "portland cement"


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## Owltech (Feb 14, 2019)

use just cement then. dry


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## Yggdrasil (Feb 14, 2019)

Hi Ashir.
Boe ash from Wikipedia:
https://en.wikipedia.org/wiki/Bone_ash

But is as said, basically burnt bones ;-)


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## gaurav_347 (Feb 15, 2019)

ashir said:


> magnesium is too much expensive here. but plane portland cenent will work. if anybody know the other name of bone ash used in pakistan then must inform me. and here is no label of portland cement, its just written "cement", but i hope i can find some cement with labled as "portland cement"




Search for 53 grade portland cement (Its white cement) . Take the regular cement and the white cement in 50/50 proportions . Screen this through a fine mesh so to avoid any lumps. Mix in some water but not too much and make your cupels. Once the cupel is made take a cloth piece drenched in water and smoothen out the surface of the cupel . let the cupel dry out for 24 hours and then proceed .


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## gaurav_347 (Feb 15, 2019)

This is fairly large size of the cupel used for large scale cupellation.


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## ashir (Feb 15, 2019)

gaurav_347 said:


> This is fairly large size of the cupel used for large scale cupellation.



nice to see ! but no one knows about plane portland cement. here i search in market today( as maximum markets are close on friday in pakistan) i ask them for white cement so i can find any marked label etc, but one give me wall putty, and some plaster of paris marked,packed, white powder! normal cement isavail easily here, but no one can [email protected] here it is plane portland cement" 
may be i can find this from larger cities!


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## ashir (Feb 15, 2019)

its too much confusing! ( same as bone ash)


here is this avail in karachi only. no grades mentioned , just 2 terms! normal cement, white cement!
even contacting with cement maker companies , no one can guide!!!!!


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## gaurav_347 (Feb 15, 2019)

you can even make it out of normal cement . White cement just gives it extra strength and gives it smootheining on the surface. You can use plaster. Try this brand as it is imported in INDIA .

https://www.indiamart.com/proddetail/opc-53-grade-pakistan-cement-d-g-khan-elephant-brand-13075159512.html


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## Shark (Feb 15, 2019)

this might help....









Portland cement - Wikipedia







en.wikipedia.org


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## ashir (Feb 15, 2019)

thanks gaurav and shark!!! got it and going to buy it. here is another request to gaurav'
must start a thread about coal and small tilting furnance, you show in a post named" smelting in india"


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## Goldenfinger47 (Aug 10, 2022)

butcher said:


> I use sheetrock for dirty melts, to save melting dish's, but the dish's for higher grade material and bone ash for lead cupling.


Sheetrock as in the stuff tapers use?


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## goldshark (Aug 10, 2022)

To get a good quality bone ash, you should boil all bones for at least an hour under a roiling (hard, intense) boil. You want to remove the gelatin. Then calcine the bones to a complete calcine ( 900 degrees C.), white hot for 1 hour, longer for larger bones. Crush to all minus 100 mesh.Mix with 10% cement, just enough water to get the material to bind, press to desired shape and size. Most mints required the cupel to dry dry for 2 years before use. Immediate use (within 2 weeks), is not recommended, due to shrinkage drying, cracking, and exploding possibilities. If it can be purchased any where, a manufacturer can usually do it for much less than you can make it.
Sheet rock, plaster of Paris, and calcium phosphate are pretty much the same thing. I have never used it for cupeling, so I don't know how well, or what effects it may have on a lead button.


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