High melting point gold alloys

I was given one of those Italian horns from the seventies by my
father to do with what I may. It had two small genuine diamonds in
it but was not marked. Well I melted it down and it seemed to take to
long to melt and did some weird things between solidus and liquidus
like forming a skin kinda but when cooled it remained gold colored.
I diped it in nitric and there was no reaction. It seemed a little
hard to roll without cracking but not too bad.

Regards
Chris Makin