The pieces I’m about to cast are 6 mm x 6 mm x 1 mm thick. I
would also like to try casting these in purple ( 750 and 250 Al ).
Whether you will be able to prepare that 18K purple material
will depend a GREAT deal on your equipment. The aluminum very
much wants to just oxidize. If it does that, you’ll end up with
useless crumbly yet hard and brittle gunk, not a nice piece of
purple material. The folks I know who’ve done it successfully
have all used equipment that allowed melting and casting
completely in the absence of any oxygen. Usually, this means
induction melt under inert gas shielding, or better, in vacuum.
Remember, too, that the 18K intermetallic compound of gold and
aluminum is not even slightly ductile or malleable. It
resembles, in working properties, a lapidary material, or carbide
etc. You can solder to it, with proper fluxes, and grind it to
shape and polish it. But you cannot flex, bend, hammer, or
otherwise work it.