Don't know if any of this might help, but for what it's worth, here's my comments;
All of the cracking problems you are experiencing are directly related to melting old gold. It generally gets contaminated with elements that destroy gold's ductility. Don't recall if it was this thread, or another, but all of this has been discussed before. If you want to process 14K gold, which is perfectly acceptable, you're going to have to start with gold of known ancestry. Even melting solder joints can lead to problems, which eliminates a lot of gold made items.
Annealing happens instantly----there is no need to hold gold at an annealing temperature. Get it dull red and quench in water, which, in your case, will eliminate the boric acid coating that was applied.
If you work with pure gold, you need not worry about fire scale. If you get any, it's because the gold isn't pure. Fire scale is the result of oxidized base metals within the gold alloy. They can be the source of the cracking you have experienced, although I expect that they are just a contributor, not the sole cause. How long you hold gold molten is important. If you can't get your gold up to melting temperature readily, but must heat it endlessly, that can be troublesome. Heating with a reducing flame is the best of all worlds, but it requires a large heat source, for a reducing flame tends to be much colder than an oxidizing flame.
Jewelers that uphold good practice do not melt old gold for re-use, and, indeed, rarely melt their gold more than once. What little gets re-melted tends to be just the sprues from previous castings, which are generally well cleaned in the pickle pot before being melted. The well pickled sprue is generally a small percentage if the gold that is melted, so it is well diluted and consumed by the new castings. By continuing this practice, gold of good quality can be assured, with no waste returned for refining.
For the record, it was VERY common to receive sprues from my customers. If they had the slightest problem with inclusions in their castings, any remaining gold, and even, on occasion, the resulting castings were submitted for refining. Pure gold eliminates a lot of problems.
Someone else recommended pouring the gold into a stainless steal container such that I would get a thin layer. I tried that but it did not come out thin. The steal deformed and the gold did not flow all over. And still fire scale. Not sure what temperature I should have been at. Was at 1850 F.
Nonsense. You can NOT get gold to pour a thin layer, full stop. You should also never pour gold to a metallic surface unless it has been well treated to prevent contact (and soldering) of your gold to the surface. If you want thin gold, it must be rolled. As advised, above, start with gold alloy of proven purity and no multiple melting.
Harold
