Surely you will get much input, Noel…
First -- almost everything we cast is injected. Is it hopeless to
get a good polish on injection waxes, pre-casting? I am not
producing these waxes myself, and I do not want to pressure the
wax person unfairly, but the finish is not what I am used to, on
hard carving wax. There is quite a lot of clean-up after casting.
Good waxwork means removing flashings and such. That’s easy to do in
wax, and much more work in metal. Since the rings are going to be
filed all over in finishing, we just don’t worry so much about
"polish" as long as it’s clean. You can use an old nylon hose to
polish injection wax, if needed. Just rub it.
Second-- Recent castings have had what the boss says is called
"spalling"-- networks of raised ridges that look almost like veins.
What can be done to correct this?
That’s because the investment wasn’t thoroughly mixed, and there’s
free water in the mix. Mix it thoroughly, and then mix it some more.
I tshould be perfectly creamy and homogonous. There could be another
reason, but unmixed investment is almost 100% the answer.
Last, today's silver flask contained 8 pieces-- 2 rings and 6
flat, coin-like charms-- and they came out with varying degrees
of pitting on the surface. Some were hardly affected; one was so
bad in places that the pits were too large/deep to be sanded out
without wrecking the piece. This was pretty evenly distributed
through the flask, and did not look like a typical porosity
problem. The porosity I am familiar with is generally close to
the main sprue, and is not confined to the surface. Though, in
fairness, I don't actually know what causes the familiar
porosity, either. Thoughts?
Sounds like incomplete burnout to me, but it’s hard to always pin
down the reason for raging porosity. Overheated metal, maybe,
probably incomplete burnout. Little bits of carbon scattered around
Oh-- and one more question-- Is it really an absolute no-no to get
even the tiniest bit of metal with solder on it in a casting? What
does it do, other than potentially lowering the karat or degree of
purity you can claim? We don’t use silver with solder on it, and we
always use “plumb” gold solder. We take a pretty casual view about
scrap metal and rarely have problems. I know what "the book"
says… I mean PRETTY casual - a bit of solder here and there
doesn’t usually mean much. We won’t cast chains… It’s the cadmium
repair solders that get you, and we don’t use those.
Casting is an art - we’ve been lucky or skilled enough to not have
serious problems in a long time. But it happens… Thanks a lot,