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Powder separation

Hello, I have been lurking for a while, as well as studying the
archives, and have found lots of useful (thanks,
everyone!). Now I am interested in some specific I am
producing a line of miniature bronze sculptures (100 mm scale), and
have been pouring the wax injection molds with RTV polyurethane. Since
my models are epoxy, cutting the molds scar the surface, so I have
been using the plasticine separation method, with two (or more) pours
for each mold, and have found this method to be messy and tedious. It
looks like powder separation molds would be the better way to go for
me, so… I would like to know what people would recommend for mold
compounds, both RTV and vulcanizing (I do not yet have a vulcanizer),
separation powders, and any special tricks or hints for packing the
molds and producing successful powder separations.

Thanks in advance, Jack Reisland

Hey Jack, Go to Contendi 1-800-343-3364 They have mold compound called
Moldex.It should work for your app. It works in a vulcanizer but if
you can press the mold frame between two sheets of aluminum you can
use an oven.It takes about an hour at 350 degrees F.You use Powdered
Mica as a seperating agent which Contendi also sells.I have used their
Moldex compound for 12 years with great sucess.Best J Molrey Coyote Ridge Studio

Dear Jack, I would like to respond to one section of your last
message. In regards to your question of RTV vs. Vulcanized molds,
these two compounds although similar in purpose, serve differently.
RTV molds are obviously room temperature vulcanized molds, which gives
you the ability to create a wax master and produce a mold without the
risk of melting the master. Now as I am a firm believer that you can
yield better detail from a RTV mold, these are not production molds.
RTV does not have the tinsel strength of a vulcanized mold. I would
recommend creating your original piece, if you do not already have it,
from wax. Make an RTV mold, and shoot some injections. You will cast
those until you have a good piece that you can make your new master.
You will take that master and create a vulcanized mold that will serve
as your production mold. You must account for shrinkage along the
way, which can vary based on wax type and mold type. All of this
unfortunately is not as easy as it sounds if you have not packed and
cut molds before. Rio Grande carry’s some very good videos on mold
making that I feel would be very useful for you. Always keep in mind
the cast ability of your patterns when originally spruing your master,
and take into consideration its ability to drain during burnout. Since
I am not aware of your current casting method, I can not intelligently
make any suggestions to that at this time, however, be aware that
different casting methods require different spruing and treeing
techniques. One last recommendation, would be to get yourself a clear
RTV compound to start out. This will give you the ability to cut a
few molds while viewing the master internally.

Good Luck!
Rusty Heath
Technical Support

Hello Jack, Try some oil on the object very thin and then Talcum
powder like baby powder, richly applied.

Martin Niemeijer

Hi Jack I use to make my molds with two aluminum sheets with drilled
holes in each corner in which I put 1 bolt and 1 wing nut respectively
in each hole then I put my already packed frame with castaldo silicone
between both aluminum sheets and hand tight each wing nut, and put it
in a toaster oven at 350 degrees I do not use C-clamps . If you want
some more about how to use this process go to and ask for the castaldo technical bulletin.


Hi Jack Go to and ask for the castaldo fact sheets
about mold making to be delivered to your address . Or you can see them
on-line under this subjects;

10 “An Easy And Inexpensive Way To Make Jewelry Molds At Home”.

11 “How To Duplicate Your Jewelry”.

12 “Jewelers With Spunk Beat Out The Spelunker”

There is a big bunch of invaluable about mold making
there. Marco