smelting difficulty

I'm having some difficulty smelting gold out of the precipitate from the
cyanide process from scrap gold. I first cook the filters down to ash
in a crucible with a propane torch. Then, I got some cupels to smelt
that ash. I do get gold out of it, but I also get a greenish-black
glassy substance that is impossible to remove from the cupel, and pretty
hard to get out of a crucible, either. What IS this stuff? Is it some
gold-bearing salts that just need to be cooked more to burn it down to
gold? Is it something combining with the flux? (I'm using borax flux
that I got for brazing.) Am I using too much flux, or not enough?
I've already destroyed one cupel, and it is hard to separate the
refractory from the gold and the green glop. The green glop melts
easily under the torch flame, maybe at 600 C or so.

I'm doing the smelting with Oxy-Methylene (generic MAPP).

So, any tricks to make this easier would be greatly appreciated!

Thanks,

Jon

Sorry for multiple post. I swear I didn't hit the button
3 times! And, the torch is Oxy-Propylene.

Thanks,

Jon