I have a question about lost wax casting. I’ve probably cast less than ten
pieces so far, all small waxes in 2 1/2 x 2 1/2 flasks casting sterling
silver. Casting single pieces at a time also. I am wondering if anyone out
there does this on a regular basis and is doing it sucessfully without
porosity problems. Sterling seems to be more prone to this than gold. Any
tips or advice on how to get porous free casts would be really helpful.
I usually use a 2 1/2 inch flask. Today I was using a 2 inch flask.
Normally, I can get up to a half dozen rings into such a flask. Today I was
casting links for a tennis bracelet. Don’t do much sterling. In fact I don’t
sell any silver. Any silver I use is restricted to models or prototypes.
As for porosity, I still get some, but I have found that what I do
get I can remove with a burnisher. Usually a rotary burnisher running on the
A couple of things that seem to be of major importance in
preventing porosity in the first place. Flask temperature: I usually try to
cast yellow gold at about 900 degrees F. White gold a little hotter. Heavy
pieces a little cooler. Lighter pieces a little hotter. Of equal importance
is spruing. Perhaps more so. I try to use as heavy a sprue as I am willing
to cut with a jewelers saw. Some people say that it should be as heavy as
the heaviest part of the casting. Probably good advice, but I haven’t gone
this far. One thing to remember is that as the casting cools, it will
contract. If there is a heavy enough sprue, the sprue can continue to feed
metal to the casting. Another thing that I can’t prove, but I believe is so
is that turbulance will affect the quality of a casting. This means anyplace
where metal makes a particularly violent turn or is pinched through a small
sprue, there will be problems.
So in a nutshell, I look for temperature, cooling effects and
I’m sure a few other people can add a lot.
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