Does anyone have any tips on how to us one of these successfully.
I always seen to get air pockets or the gold only goes part way
down before solidifying.
First, oil the mold surfaces lightly with something such as machine
or motor oil, or coat with a layer of soot, such as from a plain
acetylene flame without oxygen. If using oil, don't over do it. You
want a thin film of oil, not a wet puddle of the stuff. Wiping the
mold with a rag or brush that's got a bit of oil on it, just enough
to leave a visibly oiled surface without excess, is ideal.
Then preheat the mold hot enough so that if oiled, the oil starts to
smoke. With soot coating, you don't get the smoke as an indicator,
but still preheat the mold about the same. Either way, fully preheat
the mold fully, then heat the upper portion of the mold slightly
more, which aids in getting the metal to solidify at the bottom
before it does so at the top. Progressive solidification from bottom
to top is the goal. Not sufficiently or properly preheating your
mold is probably your biggest problem.
Support the mold with a little something, a nail perhaps, under one
end, so the mold is slightly tipped. This helps air escape as the
metal tends to flow down one side.
And make sure your metal is hot enough. If either the mold or the
metal is not hot enough, the metal can freeze before fully filling,
and this can appear as gaps or voids.
Pour in a steady stream, slightly slower than the mold could
actually take the metal. You want the metal to fill from the bottom
up, not all at once. If all at once, you can tend to get voids
running down the center of the ingot. If poured slightly more gently,
that shrinkage void will be mostly confined to the top end of the
If you are torch melting the metal, keep the metal fully covered by
the flame during melting, and try to keep both the metal in the
crucible AND the pouring stream also protected by the flame during
pouring. This will help to reduce problems with defects in the metal
due to oxidation, especially with silver or lower karat golds. The
flame used should be at least slightly reducing (soft), and can be
quite reducing, if it will still get the metal hot enough.
By the way, in judging your ingot, if it comes out of the mold
looking totally bright and smooth, without any of the texture of the
mold, you probably did not have something, either the metal or the
mold, hot enough. It's bright because it's smoother than the mold
surface on account of it's solidifying before it could fully form
itself to the surface of the mold. This may still be a usable ingot,
but you'll get better ingots if the metal can more fully conform to
the mold surface, texture and all.
Hope that helps