Although you can make one material work for most every design, one
mold material isn’t the best choice for every design. These are the
pros and cons as I see 'em:
RTV. Perfect for molds of wax, organic and plastic originals, or
where shrinkage is a problem. The clear RTV’s make cutting easy
since you can see where you are going. Waxes release beautifully.
It’s a little more expensive. I find it less than ideal where lots
of flex is necessary on an oft-used mold. You have to wait for it to
cure. You need a vacuum.
Vulcanized silicone. Shrinks less than vulcanized rubber, for the
most part. Packs very quickly. You can use powder separation. If
you are new to cutting molds, the fact that there are nearly
see-through varieties is a plus. Where a rubber mold might stick in
a design, vulcanized silicone will, most often, release beautifully.
It doesn’t oxidize silver masters (better for duplicate molds). It’s
a hair more expensive than rubber. You need a vulcanizer that will
get hot enough. You need a metal master.
Vulcanized rubber. Inexpensive. Powder separation is an option.
There are some good kinds out there that release well without having
to overuse spray or powder. You need a vulcanizer. You need a metal
If we are supplied with a metal master, we’ll almost always use a
vulcanized mold. They’re less expensive and we can be injecting
waxes that very day.
The Alchemist Casting Shop - platinum, gold, silver, bronze