My new crucible won't be here for another week, so in my impatience and in the spirit of experimentation I opted to melt up the cemented gold in a potato
Produced this rather sorry-looking little fella, just over 1g:
View attachment 67515
The potato crucible works but not very well, the gold refused to melt properly to a liquid, it just glowed dull red and gradually came together in a lump. I think a lot of heat was being wasted in cooking the potato, I just couldn't get it hot enough. I'll melt it up again with borax when my crucible arrives.
All good fun and my 1oz goal is a small step closer
Budget/DIY heat-resistant materials for small sample melting (not great, some not even good, but usable in desperate situations):
Cement - regular powdered cement for making concrete is naturally heat resistant - as it is dead-burnt at temps exceeding 1300 °C. If you press the powder into some old tin can and make smooth bowl shape using some spoon or whatever, you can melt things in it. Yes, it is "fragile" and easily disturbed, but it works OK. You can mix it with silica sand (regular playsand - but dry it first to avoid popping) and then after shaping it, sprinkle some borax on top of everything.
Do not use any water in the shaping process.
Borax tend to glue the surface together, but be gentle with it and use as little as necessary to make good glazy surface. Otherwise it will be very viscous and bead of metal will "drown" in the viscous borax-cement-silica goo (nothing terrible, but inconvenient).
Magnesia firebrick - used for lining furnances/stoves etc. In the old days, in public/industrial spaces, large electric heating units were installed. They weighed nearly 100 kg each, because they had dozens of magnesia bricks inside - which retained the heat and evened out the temp peaks
(old soviet block stuff..., maybe not applicable to UK). This was a good source of MgO bricks, which can be cut with angle grinder to appropriate size and holes ground into them using masonry drillbit in the regular (not impact) drill. Prone to thermal cracks when not heated evenly, but withstand temps exceeding 1900 °C.
Silica glass - in "emergency" cases, you can use chips of silica glass for melting small samples of gold etc. All halogen and high power lightbulbs are made of fused silica (due to temperature resistance. If you happen to have some in hand, you can prop it into some sand and use it as miniscule crucible
(what I will say, sometimes desperate situations require desperate solutions)
High density charcoal - coconut shell charcoal is usable for this purpose, but you need to properly heat it red beforehand to avoid sparking and spitting. It comes in little cubes used for smoking shisha. If forming ash is the problem, you can sprinkle some borax during the melting to keep it down. Advantage is - when the thing lights up, it adds some heat from the bottom of the charge and aid melting
