Back to Ganoksin | FAQ | Contact

Castaldo VLT Blue Silicone life expectancy

Does anyone know what the life expectancy of this low temp silicone
should be? Should I be remolding finished peices in red silicone
before my blue molds wear out?

Chas Hofmeister

Dear Mr. Hofmeister,

This is Michael Knight at CASTALDO.

The life expectancy of our VLT rubber after it has been vulcanized?
Just about forever. Or certainly a very, very, very long time.
Centuries? I’ll let you know more about this in a few hundred years.

If you mean the service life of molds made with this material, then
the answer is: Thousands of injections, but of course it all depends
on how complicated the design is, if you have cut the mold to make
wax removal easy or stressful on the mold and how rough you are in
pulling waxes.

A second mold made in some other compound would suffer from the same
user variables and would have the same service life.

Michael Knight

Chas, why not just get more? It should be no trouble for you, you’re
pretty good at it at least for now, and of course things can change
quickly in this market. Most low temp and RTV molds deteriorate
fairly quickly almost unethically if you know what I mean and I’m
sure you do!!

Kenneth Ferrell

Thanks Michael,

I did mean service life of the mold, mostly, but also wondered if
the cured molds had any stability issues as it is a low temp product.
I’d just hate to store away molds only to discover years later that
they’ve crumbled or deteriorated.


Most low temp and RTV molds deteriorate fairly quickly almost
unethically if you know what I mean and I'm sure you do!! 

“Unethically” seems undeserved. materials are what they are. Use
them knowing this and all is as expected.

For the record, I’ve got standard vulcanized molds made from Castaldo
yellow label rubber over 30 years ago which, though they’re slightly
stiffer than they were when newly made, are still quite servicable.
I’ve also got some RTV poured Silicone molds made from GE silastic E
rubber, made perhaps 25 years ago, which have become too stiff and
crumbly/cracky to work at all any more. So at least this material
(which may not be as good as current silicone rubbers) does appear to
have less permenance than standard vulcanized rubbers. But those
molds were still usable up to fifteen years after they were made, and
maybe longer. That’s not all that bad, in the end, especially since
those particular molds were being used to inject higher temperature
carving wax, not the typical lower temperature injection waxes… My
more recent silicone rubber molds, most made with vulcanized
silicones rather than the RTV versions (though there are a few of the
poured ones too), go back at least fifteen years, and even the
earliest of them, made in the late 80s from a red silicone from
Contenti, are mostly still just fine. None of them have been used for
high volumes of injections, so they’ve not been subjected to high
usage, but simple time hasn’t seemed all that damaging to them. I
don’t consider these to have deteriorated all that much, never mind
any version of “quickly”.

Peter Rowe

Dear All,

This is Michael Knight at Castaldo.

I’m not sure who Peter Rowe is responding to and I certainly don’t
want to get into an arguments with anyone.

But I don’t think we can all understand this thread unless the
writer can define a few things:

  1. What do you mean by “deteriorate”? Rip and tear? Disintegrate?
    Melt? Please let me know in more specific terms.

  2. What do you mean by “fairly quickly”? Weeks, months, years or
    decades? Or maybe you mean the number of injections. If so, how many
    do you mean?

  3. And what do you mean by “unethically?”

I’d be happy to hear any complaints about our low-temperature
vulcanizing silicone rubber or any of our other products. That’s how
we make improvements-- by listening to customers.

Obviously, I don’t think our product deteriorates fairly quickly and
is sold unethically. I’d like to hear more about this.

Michael Knight

That is very interesting Peter as I have Dow Silastic RTV molds made
from the L and the E that are over thirty years old and are the same
as the day they were made. I also use high temp carving wax in my
injector periodically. I wonder what the difference is. I see no
cracking or hardening what so ever. I have been using the stuff since
1976 and have only recently switched to other brands when I found the
Dow product too difficult to obtain, not to mention the prices. Very

Frank Goss

In reference to Castaldo’s VLT rubber and Silicone rubber expectancy
in general as well as organic rubbers and their uses…

Any heat cured rubber, which means all of Castaldo’s vulcanized
rubbers including VLT as well as Contenti’s Red Silicone are all
extremely long lasting and excellent for production purposes. Since
I have a factory with the ability to run some 10,000 pcs per day, I
can state with certainty that these are the best, longest lasting
rubbers for production and are also just as good for small volume
/small quantities. The Organic rubbers like Castaldo Gold label (
not silicone based) have the best tear strength resistance of all the
various types of rubber. That tear strength and elasticity becomes
very important when making extremely complex molds that have spiral
plugs and areas that really need to be tugged on when being removed
from a complex wax pattern. To use this rubber to it’s fullest
extent in those types of molds requires a very good mold maker with
lots of experience. This rubber can be used for less complex items,
but it is not neccessary in those cases.

Castaldo VLT and other heat cured silicones:

The Castaldo VLT is a really good very low shrinkage rubber… It is
important in all low temp rubbers to make sure that your vulcanizers
are properly calibrated and that you follow the instructions. (
calibrated vulcanizers are important for every type of rubber) VLT,
as with all heat cured silicones are very easy to cut, Knife blades
last longer when compared to cutting Organic rubber. Wax does not
stick to silicone rubber. Powder is used to release the air through
the hand cut vents in the mold. That is the primary purpose of the
powder… this does a far better job than any liquid release. Liquid
releases might give a great shine to a wax, but it is actually not an
air release agent… it will tend to seal the air in and this could
cause minor areas to not fill as well as they should.

Silicone rubbers don’t have as much tear strength as organic rubber,
however, in 95% of all applications, Silicone rubber will be more
than adequate. The wax will release from the mold more easily, making
the tear strength not as important a factor in most molds that are
made. The molds are easier to cut and vent, and can easily be powder
seperated instead of hand cut. Production is and can be greatly
increased in most cases by using Silicone molds… Mostly because the
wax releases so easily if the mold is correctly made. We prefer using
heat cured silicone molds for 95% of the molds we make because they
don’t dry out and they last for a very long time. How Long? I was the
original developer of heat cured silicone molds for the Jewelry
industry about 30 years ago while I was working for a jewelry supply
company as a lost wax engineer designing jewelry machinery, materials
and supplies. I still have the very first test molds from back then
and I still make a few products with those molds… How many
pieces… how about over a million wax injections from 1 set of molds
( a set being 10 molds of the same piece so we can handle the

I also have some castaldo gold label molds I made 40 years ago and
those work also…

Most of the Silicone we use is Castaldos VLT for low shrink
applications and Contenti supply’s Moldex red Silicone which has a
higher shrinkage and makes a slightly stiffer mold.

Castaldo has many other types of Silicone mold rubbers for many
differrent applications. Consult Castaldo’s website for applications.

There are other rubber manufacturers and other types of rubber other
than Organic and silicone. I have not gone into any detail about
those due to the fact that I have to get back to running my

I will say that you can use 2 part poured rubbers of which some are
silicone based. these are good for copying wax models and some
organic materials. They have their particular uses, But by and large
are not commonly used for production by any major manufacturers.

Hope this is helpful,
Daniel Grandi
Racecar Jewelry Co. Inc.

We do all forms of model making, casting and finishing for people in the
trade in a wide assortment of materials and metals. Contact:

The Organic rubbers like Castaldo Gold label (not silicone based)
have the best tear strength resistance of all the various types of

I’m particularly fond of Castaldo Gold myself. One other thing about
molds and rubber - you can melt rubber molds with a hot poker or wax
pen. You can (in theory you shouldn’t have to, but this isn’t
theory) melt away porosity, cracked ring shanks that have been
molded, beef up ring shanks, remove engraving, thicken sheet metal -
all sorts of things. Doing this almost always applies to remaking
old rings, duplicating Grandma’s wedding ring, and stuff like that.
You can’t melt silicone molds at all, at least none I’ve
encountered. Sometimes it matters…