buying a small crucible

this is to melt some old gold into a lump. also would it be alright to purify old dental gold?

Here in the States, you can buy clay dishes from jewelry supply houses. Gold is generally not melted in large volumes, so a crucible isn't really necessary. A torch is used with the dish instead of a furnace. Clay dishes are fairly rugged if you start properly. Warm it slowly, to dispel any traces of moisture, otherwise it will crack. Once well dried, warm it to a red heat and sprinkle some borax on the dish until it forms a shiny skin. That prevents the gold (alloy) from sticking to the dish, and also absorbs any oxidation. This is an important step and needs to be repeated as the dish is used.. The melted allow will run poorly on a dirty dish.

How do you intend to purify dental gold? It typically contains gold, silver, platinum and palladium, depending on the alloy. There are several formulations, each with a specific application. If what you have is silver in color, it's more likely to be a high temperature alloy (not precious metal) that has no value to you. Anything with value is yellow in color, although there are, in (very) rare instances, white alloy precious metals dentures. They're usually made from the platinum group and are far more ductile than the non-precious metal types.

The traces of platinum group in yellow dental gold can be worth as much as the gold itself, and they don't separate without a struggle. You could heat the gold excessively and introduce chlorine gas, which would eliminate everything but the gold if you stopped at the right time, but you're risking death by using chlorine in that manner. That is known as the Miller chlorine process and is usually accomplished in huge volumes. Gold is purified by electrolysis, but you should start with relatively high purity in order for that process to work. In the case of dental gold, you'd be best served to process it chemically, which involves the use of nitric, hydrochloric and a trace of sulfuric acid (which can be eliminated if there is no trace of lead present). It's not hard to do, but requires considerable discipline in following "the recipe", and may well be beyond your ability if you're interested in your personal safety. You must deal with the acid fumes, which can be lethal.

If you think you can purify gold by heating and separating by gravity, you're wasting your time. Rarely do metals stratify at heat. That occurs only with metals that refuse to alloy.

Harold

There is a chap who seems to have them on UK eBay most of the time. Also gold ingot moulds. Here is an example:

AWEM

thanks, as soon as i saw it, the item, i bought it.

so as my friend says who makes dentures, it is best to sell it on to some one who does this for a living.