Bone Ash Binder for fireing DIY cupels

[Anonymous]

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

gustavus

 

[goldsilverpro]

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.
https://www.google.com/search?tbo=p&tbm=bks&q="cupels"+making

 

[Anonymous]

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

 

[qst42know]

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.

 

[4metals]

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

 

[goldsilverpro]

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.

 

[qst42know]

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

https://books.google.com/books?id=A...ct=result#v=onepage&q=portland cement&f=false
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.

 

[EVO-AU]

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

 

[butcher]

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.

 

[Wyndham]

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

 

[shadybear]

So where can you find or buy these molds?

 

[Anonymous]

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

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

 

[qst42know]

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

 

[Anonymous]

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

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.

 

[qst42know]

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

 

[EVO-AU]

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

 

[solar_plasma]

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

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

 

[NobleMetalWorks]

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

 

[bmgold2]

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.

 

[bmgold2]

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.