Success. The buttons are casting nicely :) I have the quantity of metal just about right and the next step will be making more moulds so I can cast a few at a time.
The basic process is as follows:
The mould is dusted with talk then warmed under a wheat bag while the metal is melted over a low gas flame. When the metal is melted nicely and really fluid I heat the lip of the mini fry pan crucible and quickly pour the molten metal into the mould, wait a minute or so and then lift the new button out.
The consistency is pretty good, though if you look closely, no two are identical, which is kind of the point of hand crafted things.
I will be undercoating them in a mat black paint, then spraying them in a nice gold paint and dry rushing with an antique gold to bring out the highlights. Then I'll attach button backs and pop them on the as yet unfinished sleeves :).