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kenzo

Member
Joined
Nov 3, 2023
Messages
13
Location
Canberra
Hi

Moving away from all the harsh acids until I get a fume hood, I've decided to cupel for the moment.

There seems to be a bunch of sizes.
i.e. 7AL Mabor, 7X Mabor, 8A Mabor, etc

Can someone explain what these mean?

Thanks
Kenzo
 
I just did the math and a 10" cupel could process about 16 ounces of karat scrap and you would end up with a doré bead containing all of the Gold, Silver, and PGM's that were contained. Unfortunately typical jewelry processed this way would need to be inquarted because the Silver content would be too high for a gold dissolve, but it gets all of your Silver in one place and the Gold could be cleaned up nicely with a single aqua regia dissolve.

The lead fume emissions will be about 10% of the lead used but, if this were done on a larger scale, a bag house dust collector like the type welders use to remove fumes will collect the Lead emission.
 
So I got size 10s and have obviously tried too much on my first go. 32g of gold filled+100g of bismuth.

Just wondering if anyone knows what the yellow oxide is likely to be?

Next load will be about 5g of the gold filled and 50g of the bismuth. Hopefully I can get a button out.
 

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kenzo said:
So I got size 10s and have obviously tried too much on my first go. 32g of gold filled+100g of bismuth.

Just wondering if anyone knows what the yellow oxide is likely to be?

Next load will be about 5g of the gold filled and 50g of the bismuth. Hopefully I can get a button out.
Click to expand...
Also looks like a melt from a certain fraction of people, selling Gold cheap, such as the ones claiming to be wealthy folks from Dubai.
 
goldshark said:
Also looks like a melt from a certain fraction of people, selling Gold cheap, such as the ones claiming to be wealthy folks from Dubai.
Click to expand...
It was only about $35 a Troy ounce so I'm not overly concerned.


I am concerned that my cupels are cracking tho'

I heat them in the Vevor furnace before adding the "gold" and bismuth. Maybe I should heat them on top of the furnace first.

I don't think they get enough oxygen with the lid on so I keep switching between on and off for the lid. Is there an oxidiser I can add that's not a major constituent of gun powder or any other explosive?

Let's just say that purchasing stuff out of the ordinary could cause trouble for me. 🙄😳
 

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kenzo said:
It was only about $35 a Troy ounce so I'm not overly concerned.


I am concerned that my cupels are cracking tho'

I heat them in the Vevor furnace before adding the "gold" and bismuth. Maybe I should heat them on top of the furnace first.

I don't think they get enough oxygen with the lid on so I keep switching between on and off for the lid. Is there an oxidiser I can add that's not a major constituent of gun powder or any other explosive?

Let's just say that purchasing stuff out of the ordinary could cause trouble for me. 🙄😳
Click to expand...
Whether it has a lid or a door it should be cracked open.
A small fan blowing in the direction of the crack might help too.
Why is there liquid in the last picture?
 
kenzo said:
It was only about $35 a Troy ounce so I'm not overly concerned.


I am concerned that my cupels are cracking tho'

I heat them in the Vevor furnace before adding the "gold" and bismuth. Maybe I should heat them on top of the furnace first.

I don't think they get enough oxygen with the lid on so I keep switching between on and off for the lid. Is there an oxidiser I can add that's not a major constituent of gun powder or any other explosive?

Let's just say that purchasing stuff out of the ordinary could cause trouble for me. 🙄😳
Click to expand...
Pre heat your cupel to at least 700F for at least 15 minutes. Probably moisture trapped inside which can't escape, once the metals start to melt. Lucky they didn't explode. Could also be the materials used in their makeup, but usually due to being not fully cured.
 
That's a pic while it's molten in the furnace.

So, is this large enough to let the oxygen in with cupel up high like this?
 

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kenzo said:
That's a pic while it's molten in the furnace.

So, is this large enough to let the oxygen in with cupel up high like this?
Click to expand...
I'm not entirely sure. I'd put something to keep the lid slightly open.
Best is a front loaded electric kiln.
So it is the molten Bismuth in the cupel?
 
kenzo said:
So I got size 10s and have obviously tried too much on my first go. 32g of gold filled+100g of bismuth.

Just wondering if anyone knows what the yellow oxide is likely to be?
Click to expand...

Bismuth (III) oxide. Combustion of bismuth in air (500-1000 C) :​

4Bi + 3O2 → 2Bi2O3​

 
kenzo said:
That's a pic while it's molten in the furnace.

So, is this large enough to let the oxygen in with cupel up high like this?
Click to expand...
It depends on the flame you are using. Search the forum on the different flame types. I use a front door flame furnace, but I built a separate heating compartment which acts as a muffle furnace. A muffle furnace has no direct heat, other than the radiant heat from the walls, roof, and floor. A compartment within the furnace. The front door can be cracked as needed. Mine is put away for the winter, so cannot post a picture. I have thought about putting a large crucible, laying flat, or horizontal, on a special heavy rack, with a partial lid, over the vent hole to receive the heat necessary. The bottom of the large crucible could have a flat piece of steel to allow for the cupel to sit flat. It was a thought I had when I only had a furnace like yours. I built a front door furnace, for the ease in handling crucibles and cupels, for all the reasons you are encountering. Look in the pictures for an old assay furnace from Leadville I posted. These are big commercial furnaces, but you could scale down. Or just buy the electric one for a couple hundred, and be done with it. I personally like to build my own stuff, as I can then customize to my needs. I have also seen furnaces like yours, with a rack to hold the cupel in the flame of the vent. This leaves the top open for the necessary atmospheric air. Never saw it operate, so don't know how well it works.
 
Ok so I got it to work ... Eventually.
I needed the lid slightly off and when I eventually used a fan it worked quite quickly.

No gold tho'
1000009896.jpg


I asked the eBay seller and they said that it was 0.64% according to their XRF

1000009926.jpg
Wouldn't an XRF only show the makeup of the surface, not the entire lot?
 

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