Best mold material?

I’ve been a sculptor all my life, using silicone rubber from
Silicones, Inc. GI 1000 to make all my molds. Now I’m doing jewelry
pieces, and I find the rubber is just too flexible. When I push the
mold against the wax injector the nozzle goes too far in.

So I want to get set up with the very best, and most modern system
for jewelry molding there is. I have an old vulcanizer if that is
what is needed, but I see in my Rio catalogue that there are rubbers
that don’t even require pressure. I need to make molds that will last
for many duplicate parts, and capture the most intricate detail
without shrinking…

So what is the best system, and best mold rubber, and which frame
system is the best, too? Hope that’s not too much to ask. Thank you.

Larry Heyda

You can get silicone rubbers with very different properties when
cured, both RTV and ones you have to heat to cure. You can get
flexible epoxies and you can vulcanise. I tend to use silicone
rubbers and then clamp my moulds to inject the wax using a device I
got from Rio Grande. A lot of what you use will depend on how fragile
your patterns are, both the original and the waxes. I cant really
give you a rubber that does everything.

Nick Royall

I adore Zero D Zero shrink mold material. It does require a

I’ve been very happy with castaldo rubber. There is a pink “no
shrink”. However I have made a ring with a heavy bezel/border to
slip an oval flat piece down in it. I had hoped that I would not be
required to mill out the ring each time I place the flat oval piece
in it which is held by solder. However I must be trying to emulate
die struck items, because I’m finding that my molds apparently do
not retain enough precision to match the same size each time. I done
enough molds I’m tired of attempting to get a perfect fit each time
and settle for close so far. My experience is that you will not get
complete control, but this is the only design I have that needed the
close tolerance. I have several molds of really intricate pieces like
crawfish with legs and feelers that I have used powder rather than
cutting the mold. I have molded a few things I could not have cut
e.g. wasp legs, crab feelers…

Are your molds thick enough from the silicone rubber? Are you using
plates roughly the size of your molds to hold them firmly when you

Hi Larry; I like the vulcanized silicone rubbers rio has thier own
brand called delicone I use the yellow or red one, the reason that
you don’t have to add pressue is because it develops it’s own
pressure when heated. in it’s un-vulcanized state it’s like modeling
clay which is why i like it, you can make your molds without cutting,
using a mica powder to seperate them, if you’re familiar with molding
you probably know what I’m talking about.

If you don’t like dealing with rio grande…contenti makes "moldex"
rubber which is the same thing remember you will need alittle bit of
mica powder of dry teflon spray between the parts, you want to
seperate. I have also found that adding alittle bit more powder or
spray in the corners will help you start the pull-apart process.

Another good company is Zero-D products they have a wide range of
vulcanized silicone rubbers too probably a web site also, they can
reccomend if you tell them what you are doing.

Good Luck…Gregg B.

Dear Gregg, Nick, Jay and Paleo,

Thank you for your advice. I guess I need to do a little honest
research before I waste everybody’s time here. This is the first I’ve
heard about using a mica powder for separation. So I’m guessing the
process is that you mush the rubber up agaist one side of your part,
sprinkle powder on part and rubber, then mush new rubber on the other
side, enclose and heat? I better try to learn more about this from
Rio or some book. If anyone knows a good up-to-date book on making
great molds, I’d love to buy it.

I’ve always vacuumed the silicone I use, poured it into a mold
cavity surrounding the part, then cut the mold afterward with a
zigsaw cut to guarantee registration. It’s worked like a charm with
hardly any flashing.

I guess I just need harder rubber. I appreciate all the brands of
rubber recommended, and I’ll give them a try. Thank you!


Contenti has a red silicone rubber that vulcanizes. It starts out
like a modeling clay in strips about 1/8 inch thick. Vulcanized it
has incredible strength. The detail that is reproduced in the waxes
is perfect because it is self releasing and the material will mold a
fingerprint. Easy to vulcanize, I left my vulcanizer on all night by
mistake and thought the mold would be ruined. It came out perfect.
Drawback is you have to use dedicated frames that are only for the
silicone rubber. Also FYI keep the uncured rubber away from any oil
contamination. I had a vacume pump leak and ruin a few pounds of
rubber. Everyone I have referred to this material made the switch.
Buy a pound and check it out. Frank