life span of a casting mold ?

As a consumer, I've been told that a certain jeweler has been
continually using a 30 year old mold to cast gold jewelry.

I thought those molds wore out after so many pours, being made from
rubber. So you can only shoot hot liquid wax in there so many times,
then you have to make a new mold.

Is this so?

On Sun, 07 Nov 2004 21:42:31 -0800, in ¸õ (TRafferty) wrote:

As a consumer, I've been told that a certain jeweler has been
continually using a 30 year old mold to cast gold jewelry.

I thought those molds wore out after so many pours, being made from
rubber. So you can only shoot hot liquid wax in there so many times,
then you have to make a new mold.

Is this so?

It varies somewhat, depending on what type of rubber was used, and the degree to which
the mold needs maximum flexiblity. Highly complex molds may have been almost cut to
shreds in order to make a mold from which a complex highly undercut wax model can be
safely extracted, and that sort of mold may not last as long as one with a simple design
that doesn't put so much stress on the rubber when pulling the waxes out. Over time,
most of the rubbers tend to get a bit stiffer, whether or not they're used.

Keep in mind that casting wax is injected into the mold at a temperature of only about
160 to 170 degrees F. Vulcanized rubber molds are about the same durability as the
materials auto tires are made from. The wax doesn't have much effect. I still have
some molds I made in college, in the 70s. They aren't great designs, but the molds,
while perhaps a bit less flexible than they were 20 years ago, are still just fine. And
my employer, which has been in business since 1937, has a few boxes of the old molds
still kicking around. Their earliest casting work appears to have been done with sand
casting, so the earliest "molds' amount to usually simple brass metal models that were
used to make sand molds. But from sometime in the late 40s or early 50s, it appears
they got on the bandwagon with lost wax casting, and a few of the rubber molds from that
period are still kicking around, though we don't actively use them any more. Some of
them seem pretty stiff at this point, but I think I could possibly still get a usable
wax from more than a few of them.

And I've got a couple of vulcanized silicone rubber molds that are the type used to spin
cast white metals directly into the rubber for costume jewelry manufacture. (Silicone
rubber withstands much higher temperatures than standard vulcanized rubber). Those were
made using newspaper as a seperating layer between the outer layers of rubber and the
mold frame, and the papers are imbedded into the rubber, making it fun to date the mold.
Those papers appear to be from the 50s or maybe 60s, though I'm unsure since they're not
in english. The mold, if I still had a spin casting machine, would still work just fine
even with the actual molten white metals (which melt between 400 and 600 F, much higher
than casting wax.) The actual mold impressions are pretty scortched and darkened at this
point, but appear to still retain all the needed detail and have not cracked or
otherwise actually broken down.

Now, there are also other types of mold material. The room temperature vulcanizing
(RTV) types, usually silicone rubbers mixed as liquids and poured, which are useful for
making molds of things that cannot withstand the heat and pressures of vulcanization, or
when a mold with no shrinkage is needed, are not as durable as the vulcanized types.
Over time they loose flexibility and start to get too weak and easy to tear. I've got
several of those made in the late 70s still around here. About half of them can still
be carefully used, while the others cannot, having been too damaged in one way or
another. It doesn't appear to be heat from use that damages them, just plain aging of
the material, since there is little difference between those molds that were used a lot
(for injecting wax) and those that were not.

Hope that helps.

Peter Rowe

Peter W.. Rowe, wrote:

On Sun, 07 Nov 2004 21:42:31 -0800, in ¸õ (TRafferty) wrote:


As a consumer, I've been told that a certain jeweler has been
continually using a 30 year old mold to cast gold jewelry.

I thought those molds wore out after so many pours, being made from
rubber. So you can only shoot hot liquid wax in there so many times,
then you have to make a new mold.

Is this so?


It varies somewhat, depending on what type of rubber was used, and the degree to which
the mold needs maximum flexiblity. Highly complex molds may have been almost cut to
shreds in order to make a mold from which a complex highly undercut wax model can be
safely extracted, and that sort of mold may not last as long as one with a simple design
that doesn't put so much stress on the rubber when pulling the waxes out. Over time,
most of the rubbers tend to get a bit stiffer, whether or not they're used.

Keep in mind that casting wax is injected into the mold at a temperature of only about
160 to 170 degrees F. Vulcanized rubber molds are about the same durability as the
materials auto tires are made from. The wax doesn't have much effect. I still have
some molds I made in college, in the 70s. They aren't great designs, but the molds,
while perhaps a bit less flexible than they were 20 years ago, are still just fine. And
my employer, which has been in business since 1937, has a few boxes of the old molds
still kicking around. Their earliest casting work appears to have been done with sand
casting, so the earliest "molds' amount to usually simple brass metal models that were
used to make sand molds. But from sometime in the late 40s or early 50s, it appears
they got on the bandwagon with lost wax casting, and a few of the rubber molds from that
period are still kicking around, though we don't actively use them any more. Some of
them seem pretty stiff at this point, but I think I could possibly still get a usable
wax from more than a few of them.

And I've got a couple of vulcanized silicone rubber molds that are the type used to spin
cast white metals directly into the rubber for costume jewelry manufacture. (Silicone
rubber withstands much higher temperatures than standard vulcanized rubber). Those were
made using newspaper as a seperating layer between the outer layers of rubber and the
mold frame, and the papers are imbedded into the rubber, making it fun to date the mold.
Those papers appear to be from the 50s or maybe 60s, though I'm unsure since they're not
in english. The mold, if I still had a spin casting machine, would still work just fine
even with the actual molten white metals (which melt between 400 and 600 F, much higher
than casting wax.) The actual mold impressions are pretty scortched and darkened at this
point, but appear to still retain all the needed detail and have not cracked or
otherwise actually broken down.

Now, there are also other types of mold material. The room temperature vulcanizing
(RTV) types, usually silicone rubbers mixed as liquids and poured, which are useful for
making molds of things that cannot withstand the heat and pressures of vulcanization, or
when a mold with no shrinkage is needed, are not as durable as the vulcanized types.
Over time they loose flexibility and start to get too weak and easy to tear. I've got
several of those made in the late 70s still around here. About half of them can still
be carefully used, while the others cannot, having been too damaged in one way or
another. It doesn't appear to be heat from use that damages them, just plain aging of
the material, since there is little difference between those molds that were used a lot
(for injecting wax) and those that were not.

Hope that helps.

Peter Rowe

In addition to this:
A friend of me brought some samples of several hundred very old rubber
molds, which were completey stiff and hard.

I made some tests with them to get them reusable. The best result we get
after they were inlaid in hot water with sapon for two hours.
Most of them get like new.

Grüße,
Heinrich Butschal

--
www.juwelen.online-boerse.org
www.meister-atelier.de
www.schmuckfabrik.de
www.medico.butschal.de

"Peter W.. Rowe," wrote in message
. ..

Hope that helps.

Peter Rowe



Thanks for the reply. If I may, can I email you the link to which I'm
refering to. It shows the "actual" molds for the peice that is being
sold?

On , in ôõ (TRafferty) wrote:

"Peter W.. Rowe," wrote in message . ..

Hope that helps.

Peter Rowe



Thanks for the reply. If I may, can I email you the link to which I'm
refering to. It shows the "actual" molds for the peice that is being
sold?

Sure.

Or better still, perhaps, put it in a reply posting to the whole group, so everyone can
see and comment. No reason it should be just me...

Peter

On , in ¸õ Heinrich Butschal wrote:

I made some tests with them to get them reusable. The best result we get
after they were inlaid in hot water with sapon for two hours.
Most of them get like new.

Heinrich,

I'm unclear on just what, exactly, is "sapon". A solvent of some sort, or oil?

thanks.

Peter

Glycerol. Saponification is the process of hydrolyzing a fat with an alkali
such as NaOH into soap and glycerol. Lye soap like grandma used to make from
cooking fats. Glycerol is a plasticizer and a solvent good for softening
rubber.

--

Don Thompson

Remmy sez,
Count de Monet.
Unless, of course, you are Baroque.


"Peter W.. Rowe," wrote in message
news
On , in ¸õ Heinrich Butschal wrote:

I made some tests with them to get them reusable. The best result we get
after they were inlaid in hot water with sapon for two hours.
Most of them get like new.

Heinrich,

I'm unclear on just what, exactly, is "sapon". A solvent of some sort, or
oil?

thanks.

Peter

Peter W.. Rowe, wrote:

On , in ¸õ Heinrich Butschal wrote:


I made some tests with them to get them reusable. The best result we get
after they were inlaid in hot water with sapon for two hours.
Most of them get like new.


Heinrich,

I'm unclear on just what, exactly, is "sapon". A solvent of some sort, or oil?

thanks.

Peter

Sorry for my mistake. I wanted to write "soap".

Grüße,
Heinrich Butschal

--
www.juwelen.online-boerse.org
www.meister-atelier.de
www.schmuckfabrik.de
www.medico.butschal.de

"Peter W.. Rowe," wrote in message
. ..
Or better still, perhaps, put it in a reply posting to the whole group, so everyone can
see and comment. No reason it should be just me...

Peter

A jeweler out in LasVegas is trying to sell his molds for $2.25 million

http://cgi.ebay.com/ws/eBayISAPI.dll...m=383344429 3

On Mon, 08 Nov 2004 21:37:45 -0800, in ?? (TRafferty) wrote:

"Peter W.. Rowe," wrote in message
...
Or better still, perhaps, put it in a reply posting to the whole group, so everyone can
see and comment. No reason it should be just me...

Peter

A jeweler out in LasVegas is trying to sell his molds for $2.25 million

http://cgi.ebay.com/ws/eBayISAPI.dll...m=383344429 3

Wow. That's a rather healthy price for some old rubber molds...

But I see no reason they wouldn't work still.

If your planning to buy em, however, do be aware that what these produce are only the
wax models for the ornament sections of the frames. You still need to obtain or make
the frame itself, to which those ornaments are affixed. And the waxes still need to be
cast, and finished. The molds are only one step in the process. I'd guess the real
value of that auction, if there is any, is in the rights to the designs, not the molds
themselves, though it's nice to have the molds if one wanted to make more of those
glasses. Most decent jewelers, working from even just the photos in that auction, could
make new models and new molds for a cost with a whole lot fewer zeros than the auction.
So what justifies that price is the copyright (if there is one) and all the Elvis stuff
attached, if that's justification. In this world of ours, where all sorts of
copyrighted design work from fine jewelers gets copied and knocked off, often very
inexpensively, in parts of the world where U.S. copyright law is hard to enforce, or
even right here where it may not be economically feasible to prosecute, one would have
to be very sure that one was indeed able to justify a purchase like that...

cheers

Peter