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.
TR the Teacher