I'm interested in doing things more like casting a medal in
bronze, gold or silver, but with provisions for mounting stones. I
seem to have gotten a lot of negative responses about the idea.
I have had a lot of good results with sand casting, but I use it
almost exclusively for things like twigs, where it doesn't matter
much if there's a bit of porosity or flashing. However, I had a
student use it to reproduce a three-dimensional silver fish pendant
(which would be much like a medal, in terms of detail), with
excellent results-- though it took her several tries to get it
perfect. The good news is, it is pretty fast, and the original is
undamaged, so you can keep trying.
As far as tips and tricks, here's what I can think of: It helps to
pre-heat the sand mold in an oven to maybe 350-400 degrees, to help
reduce the likelihood of incomplete fill. You can't go hotter than
that without burning the binder in the sand.
It helps to hammer the sand in really hard, to get good detail and
no flashing. It also helps to put vents at the far end of the
object-- just scratch them into the sand while you have the two
halves separated. Curve them back around toward the top, then out to
the edge, as the metal doesn't like to flow back the other way, but
air doesn't mind.
It is important to pay very close attention to how the sand meets
the model in the bottom half; if there is any gap around the model,
the sand in the top half will fill it, but this produces tiny, thin
sections of sand that tend to break off when the halves are
separated to remove the model, causing lumps of metal where they
Be sure you sweep away all loose crumbs of sand before you put the
mold back together, so they don't end up in the casting.
Lastly, I have actually put a sandcasting mold in the centrifugal
casting machine and cast it, with no problems, though I always
expect the sand to fly out (it never has). Even though it has
worked, it makes me nervous, so I don't generally do it, and I can't
promise that it is a good idea. I guess you could clamp a sheet of
metal on each side of the frame so you wouldn't have to worry.
Sure, it is not the ideal way to cast-- that would be lost wax-- but
it is quick and easy, and you get to keep your original. There's
something to be said for immediate gratification.