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Silicon RTV


#1

With all of the recent discussion of Silicon RTV, I thought I would
throw out a query to see if anyone can help. I have been making
Silicon RTV molds for 25 years, and so I have used many products with
varying degrees of success. I did find at one time what I would call
the perfect silicon for jewelry molds, but production of this
material was discontinued about 7 years ago. The product was made by
Wacker Silicone and it was called Elektroguard 2755. When I say it
was the perfect mold material, I mean it had good tear strength, was
neither too hard or soft, showed little shinkage, would not react
with other materials, even oil based modeling clay, the cure rate
could be accelerated with heat to about 6 hours at 120 degrees with
no apparent adverse effect on the mold, and the molds do not
deteriorate over time. Wacker discontinued making it when it’s
costs soared (the last 8lb kit I bought was something like $300) to
the point that whatever industrial application it was used for no
longer supported it’s production. At one time I spoke with one of
the chemists at Wacked and he agreed that this material was like no
other silicon RTV on the market in that it had such great flexability
in use. I have since tried several products and while they are
acceptable for general mold making, the one area that I have had
trouble with is accelerating the cure time. I have found nothing that
I could get less than a 15 or 16 hour cure with the addition of more
catalyst or an accelerator, and usually the results were inferior to
a properly cured mold. Does anyone out there have experience with a
Silicone RTV that fits the above bill? Thank you for any
suggestions!

Best regards,
John


#2

Dear John,

I have been making silicone and gum rubber molds since 1977. I
started with the Silastic E RTV. A white fairly flexible mold
compound. This was and is too flexible and tears easily. I do
comparisons of many silicones with a thirty point comparison chart. I
get silicone samples from many parts of the world. Some Japanese
silicones are excellent. Hard to get but excellent.

I will state without question that the BEST silicone I have ever
used is Silastic L RTV. Now this stuff is hard to find. Most people
use the J RTV . The J is good but much too stiff. It look just like
the J but the working properties are the best. It does not cure
objects that come in contact with gum rubbers and objects with any
sulfur content. I compare all silicones I test to this silicone. It
will cure overnight or baked in a low temp oven. There is virtually
no shrinkage in either case. It’s almost impossible to measure 1%
shrink. Especially on jewelry.

Now I don’t make a dime on this product, but I sure wish I could.
I’ve even tried to become a distributor but they want you to handle
other Dow products. Try it you’ll like it if you can find it. I buy
mine from Stebgo Metals in South St. Paul Minnesota. They also keep
the price down to about $29.00 a pound for my mold classes. That
beats every price I’ve seen elsewhere.

Good luck and happy molding.

Best Regards,

Todd Hawkinson
www.trhawkinson.com
TR the Teacher
www.mctc.mnscu.edu/jewelry