I've been using a 20k alloy for over a year now, and I like it. I'm
using an alloy that has a 60/40 mix of copper over silver. It is a
harder alloy, and when you heat it and pickle it, it will leave a
layer of fine gold on the surface. It looks very close to 24k. but it
has the hardness (malleability would probably be more correct) of an
18k with a higher silver content. Not super hard, but not anything as
soft as 22k. It does set nicely.
You'll have to make up your own solders to work with this alloy.
There is a "pinch" of Si in the mix, too (less than 1%). I would
suggest that you experiment with a couple of different alloys, and
fine the one that works best for your style of work. If you are
purchasing pre-mixed alloys for casting, just use the 22k alloy but
decrease the percentage of gold. You may find it quite suitable for
most castings, and it can also be used as a rolling alloy. Doug
Bocas del Toro, Panama