Melting and casting gold ingots

hi just wondering if anybody out there has used the chinese graphite crucibles and molds .I just had the bottom fail putting an oz of gold into the furnace which i have been heating with coke maybe to hot .Any ideas. the crucible had been used about 10 times

Were you heating the crucible? Did you ever knock the crucible? Even bang the base to get something out?
What size is the crucible, and how thick are the sides?
Do you have this:
Or this:

Always careful to heat before use .it did distort and shrink by about a third .Yes bought of ebay. same as your pics. molds work fine

Depending on which one you have; I don’t think they are meant to be heated or placed in a furnace.

They are poor conductors of heat, the aim is to get the heat down inside of the crucible with a blow torch or inducting smelter. Or pour metal into them. There are ceramic dishes which might be better suited.
Perhaps it is just a bad design. I see some crucibles with a rounded base.

Does anyone know of a good place to buy nitric acid I want to refine my silver scrap. I think I will need about 500ml of 68-70%
best price I have found is $94 for 2.5litres but they won’t sell to the public.

It’s easy enough to set up a soletrader account with your bank online.

Check out this video, apparently you can make a smelting dish out of a potatoe (near end of video).

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hey dude i built my own and works fine but i only use a blow torch to melt it have a nice 14 gram button that i made myself great fun melting gold if ya want more info just let me no and ill find links that helped me make it

Thanks for that…I have done some research and think I am getting on top of it. Cheers

This video has a lot of tips. And some links to different simple techniques at end.
He recommends a clay-graphite combo crucible. But they are not cheap $60ish

You may have to heat up clay graphite crucibles carefully.

Another thing to keep in mind: don’t let the metal solidify in the crucible and cool all the way down. It will either get stuck, or rip the inside of the crucible apart. You may be able to let it solidify, but tip it out when it’s still very hot and soft, so it doesn’t get the chance to harden and shrink.

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Few more tips.
Heat up your casting tray, and line with a bit of oil (any will do, even WD40/CRC).
Covering your recently poured gold with Ammonium Chloride will make it shine.

When you do your first melt, pour it out onto a flat surface (non flamable) - the last thing you want is a massive lump of rock hard flux in your crucible! It can also trap your gold bead. Sometimes the only way to remove the solidified flux is with Nitric Acid!