I can't get just the mixing alloy, to use as needed, but have to buy 18K gold mixed by them. I also work in silver and platinum, which are both absolutely beautiful white metals. I have very mixed feelings about them, though. Silver is very easy to work with, and very inexpensive, a joy to use, but it is quite delicate. It remains soft even after it's been worked for a while, and it can tarnish over time.
Platinum is even prettier than silver, never tarnishes at all, but is an absolute nightmare to work.
When I draw gold wire, I can pull it through two or three successively smaller holes before having to anneal it. Platinum, however, I have to anneal every single time. Not only that, I can't even coil it up to heat it all at once, because the simple act of uncoiling it will work-harden the wire again to the point where it could crystallize and break the next time I draw it through the drawplate. I have to pass the torch along the wire, inch by inch. Not bad when it's only a foot long, but very tedious when it gets to be longer than I am tall.