This from Rainer Suss of Mintek, South Africa mintek.co.za
We can supply purple gold. What exactly do you need? Since
we're not a production company, we can only supply on a small
scale.
We can only supply buttons between 2 and 10 g each, which you
will have to get polished and facetted yourself to make
"for inlays (the same way you'd process minerals).
This is the only practical way of supplying the metal. We
normally charge gold price plus the courier costs to get it to
you as well as a manufacturing fee (~$300 per batch of 6). Any
amount less than six is unfortunately not really worth the
effort but we could make a plan if you'd be interested.
Supplying purple gold alloy for youfor casting is not
possible. From past experience the alloy is not very amenable
to repeated melting and quickly degrades in appearance.
You are more that welcome to do experimental melting yourself.
I can provide you with the composition since we do not have a
patent or copyright on it - it's in the open domain. The alloy
is simply 75 wt% gold 25 wt% aluminium. Take note that you need
to use a protective atmosphere or vacuum when melting. Also
note that once cast the metal cannot be hand worked in any way
(e.g. bending, rolling, etc. is impossible).
Finally, the purple colour is unique to 18 carat and cannot be
duplicated for 14 carat due to metallurgical reasons.
I hope this of help.
Regards
Rainer Suss, Mintek