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Retouch/filing gold castings


#1

Greetings Sunil-

Allow me to respond to your post about finished castings. I am a
professional jeweler and engraver and have practiced this trade
for 20+ years. New to this business maybe, but you hit the nail
on the head with your observations. This is where your greatest
loss of metal occurs and one of the most labor intensive areas.
You should try to have absolutely the best molds possible to
produce the best waxes that you can. The better finish on your
waxes, the better finish that you get straight out of the cast.
If you’re using rubber molds, finish your models that the molds
are made from as perfectly as possible. Better than rubber molds
are metal molds which are finished to perfection also and impart
this same finish to every wax that they produce. The metal molds
are more accurate than rubber and produce waxes(or plastic
patterns) that are very consistent with no variation, but are way
more expensive as they have to be machined. One way to sharpen up
the waxes that you produce is to try this new silicone rubber
mold material that they carry at this company everyone on Orchid
is talking about named Contenti in Rhode Island, USA. It is
different than what is generally used in the industry(Castaldo),
and is a burnt orange color. Otherwise it works the same as the
Castaldo except that if you get your masters finished perfectly,
this rubber is better at imparting this same finish to your
waxes. A mold made from a high polished master will produce a wax
that has a high polish also to start with. You can actually see
yourself in the shine that it imparts to the wax, something that
the other just won’t do. This is a very subjective thing, but if
you used each type of rubber side by side using the same master
to make both molds from, you can readily see the difference. The
better finish that your wax has, the less clean up you have after
casting. The cost of finishing the wax is nominal when compared
to the cost of finishing the metal itself after casting, to say
nothing of the metal lost in the process. Your cast will come out
in the same condition that your waxes went in with, any flaws,
etc. will be reproduced in your casted metal. I can’t stress this
concept too much. After getting your waxes up to speed and casted
with the best possible finish, you would then pickle, bomb, and
possibly electro-strip the castings. You would then polish the
castings with a vibratory, rotary, or magnetic tumbler. If your
castings are coming out with a nice finish straight out of the
cast, you don’t need to use any of the tumbling media that cuts
or removes any metal at all because you won’t get a better finish
than what you came out of the caster with using this silicone
rubber mold material.( granting that you did everything
correctly). You can tumble with steel shot for a short time and
maybe something for a higher shine like charged shells, etc. It
is going to depend on how well finished your waxes were prior to
casting once again. After any tumbling, you will have to clean up
by hand polishing where your sprues were etc., but if you cut
your sprues off with either a saw frame or end nippers, it will
leave very little clean up necessary if done properly. You would
then pre-polish everything ( using grey star, tripoli, etc.) and
set your stones. You then take the piece and do the finish polish
using rouges, zam, or whatever.

Any metal loss as a result of tumbling is recovered by letting
the fluid from the tumbler sit and the heavier particles settle
to the bottom. Filter this sludge out of solution and send the
filter papers off to the refiner to recover your metal.Any loss
at your polishing stations will be caught in your filters there-
again, send to a refiner to recover your metal.The same would
hold true for the remains of any bombing that you would do- send
it to the refiner.The absolute optimum would be to have your
waxes finished so well that all you have to do is cut your sprues
off, polish this spot or spots and polish the rest of the piece
with only rouge- no tumbling necessary, no filing necessary
other than the sprue points. This silicone rubber imparts such a
nice finish to the waxes that this is entirely possible. Just ask
Frank the Goss-inator! Regards- Ricky Low


#2

Ricky, Thank you very much for your valued suggestions.

After getting your waxes up to speed and casted
with the best possible finish, you would then pickle, bomb, and
possibly electro-strip the castings.

I am new to the terms PICKLE, BOMB & ELECTO-STRIP; can you let
me know the importance of these and the way they are carried out.

You can tumble with steel shot for a short time and
maybe something for a higher shine like charged shells, etc.

We usually do the rotary tumble polishing using seel shots but
have never know about charged shells. How does the charged shells
works.

waxes finished so well that all you have to do is cut your sprues
off, polish this spot or spots and polish the rest of the piece
with only rouge- no tumbling necessary, no filing necessary
other than the sprue points.

What is the best technique to cut off the casting / sprues in
order to minimize time and gold loss?

I thank you once again for your valued Regards

SUNIL KHINVASARA
BANGKOK
TEL 66 2 6788334 / FAX 662 2863650
Email: sunilk@ksc15.th.com