Low-melt metal casting

Jewelry Discussion
1

I have done a great deal of centrifugal casting of silver over the
years. Recently, I attempted casting some small parts (about 1oz)
for a Pocher model car using low-melt metal (not pewter). I made my
two-part mold from RTV rubber. They came out excellently. The
molds have escape paths for air, etc. However, when I poured the
low-melt metal, the resulting cast piece was covered with tiny
pockmarks or bubbles. Since I made an air escape tube in the mold,
I don’t think my mold is trapping air. In fact, the pockmarks look
more like trapped moisture. But where is the moisture coming from?
The RTV has no water in it when it is cured. I really don’t know
what to think . . . ? Do any of you have experience casting with
low-melt metal? Or do you know anyone I might contact? I need some
help. Thanks in advance for any suggestions.

Regards,
Mike Youngblood
msyblood@aol.com

2 
They came out excellently.  The molds have escape paths for air,
etc.  However, when I poured the low-melt metal, the resulting cast
piece was covered with tiny pockmarks or bubbles.  Since I made an
air escape tube in the mold, I don't think my mold is trapping air.
 In fact, the pockmarks look more like trapped moisture.  But where
is the moisture coming from?

Hi Mike, Before casting the metal, you must use talc on the mold …
preferably in a soft bag …simply tap the bag of talc lightly in
the cavities of the mold, then close the mold and pour away…should
come out fine… usually, the first shot would be to warm up the
mold. the second shot should be better… then, it can get
progressively worse as the mold heats up too much …so let it cool
a bit between pours. Hope this helps.

Daniel Grandi Casting, finishing in gold, silver, bronze, pewter for
designers and people in the trade. Contact: sales@racecarjewelry.com