# Need advice on a possible crucible



## Maget (May 4, 2022)

Hello
I came across a possible crucible that someone sell locally for around 5 USD, it is used but still in good condition, not sure what it can be even the owner could not tell.
So I told him that I will buy it next time if I will be sure it's a crucible and not something else which can break from high temperature.
Here is attached a photo maybe someone can tell if is worth to buy.
Thank you.


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## BenKenobi (May 5, 2022)

looks like a glazed porcelain crucible, not good for thermal shock, generally used in an electrically controlled furnace where heat ramp and rundown are controlled.

You have not stated your purpose on use, stick to what everyone uses, use a quartz silica melting dish, they will cope with direct flame have excellent thermal properties and fantastic thermal shock resistance, glaze with a thin layer of borax and you are good to go, cheap to replace and you can can buy a stack so you have some on hand specifically for certain metals, karat alloys, purities etc so you dont contaminate your 3N or 4N silver crystal in a dirty melt dish, that simply undoes all your hard work.

If you have an open flame furnace you have a few choices, clay graphite being the most popular and probably the cheapest, most abuse resistant regarding thermal shock, DO NOT use Borax on your Clay Graphite Crucible!!! it is highly caustic and will ruin your crucible by degrading the inner lining and you will end up with graphite contamination in your metal.

I would not recommend pure carbon crucibles for open flame furnaces, you can use it but will degrade by far quicker than using it in an electric funace as it is intended.

All crucibles have a finite life, the ones mentioned are general purpose and common.........for a reason. Stay away from exotic gear until you understand exactly what you need for your intended purpose, speak to a refractory agent regarding your needs if you will but ensure you disclose EXACTLY what your intention/application is and your equipment before you purchase anything.

Play safe

Regards
B.


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## Maget (May 5, 2022)

BenKenobi said:


> looks like a glazed porcelain crucible, not good for thermal shock, generally used in an electrically controlled furnace where heat ramp and rundown are controlled.
> 
> You have not stated your purpose on use, stick to what everyone uses, use a quartz silica melting dish, they will cope with direct flame have excellent thermal properties and fantastic thermal shock resistance, glaze with a thin layer of borax and you are good to go, cheap to replace and you can can buy a stack so you have some on hand specifically for certain metals, karat alloys, purities etc so you dont contaminate your 3N or 4N silver crystal in a dirty melt dish, that simply undoes all your hard work.
> 
> ...


Yes agree, this looks as porcelain, but I have the silica crucible and graphite one, I plan to melt with gas flame in silica one and also have a induction furnace, there I will use the graphite one.
So your advice is to not buy this porcelain crucible, because it is worse than what is already widely used right?
Thank you.


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## BenKenobi (May 5, 2022)

yeah, stick with what you have, i have been in precious metals for decades from prospecting, jewelry and refining, never had a use for anything other than clay graphite and quartz silica. I spose you could push it to bonded silicon carbide, very exxy for quality or bonded silicon carbide graphite if you can find them at reasonable prices, good quality and in the size you actually need, the bonded SiC crucibles are more resistant to fluxes, excellent thermal stability, i have never had a use for one as they will not fit in my furnace anyway as i made my own and its front loading and have never had a need to pour over 1kg. But same applies do not put a caustic flux into a crucible that has graphite in its composition if you want to pour clean metal.

Others may think otherwise regarding graphite, but from personal experience i will not be going back there regardless of what anyone thinks.


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