I have a art bronze foundry and use the ceramic shell process.
I use the coloidal silica along with fused silica flour for the
slurry. For the first 2 sand coats, I use zircon sand, for the
remaining coats (about 5 or 6) I use fused silica (35-50 mesh).
There are a number of coloidal silica mfgrs (ranson & Randolf and
REMET are 2). There are a number of different sand and fillier
materials too, depending on the metal to be poured.
I do not know about melting the metal in the cup. The wax is
melted out, the shells have to fired (I go aobut 15-20 minutes at
about 2000F or until the carbon is nearly gone, repair any cracks
and fill any drains, then fire again for 10-15 minutes just prior
to pouring and pour into a hot shell. I do have a cup form at
the top of the sprue, something to pour the molten metal into. I
melt in a crucible (currently about 85 lbs but soon up to about
300 lbs/pour). I pour directly from the crucible into the shell
form. If cast iron is used, it is often (usually) ladeled into
Mud can/has been before ceramic shell came about. Some have
played with raku type clays, incorporating straw and the like for
steam venting. “Home made” investment mixes are used by many
with as many or more mixes of just about everything, being used
in the investment. Needless to say, some work better than