Dan Saultman on sun 13 feb 05
Randall,
Your exploration into rubber as a mold making material was informative.
I would suggest that you look into a product called RTV. I believe it's
a Dow product. This rubber-like casting material is a 2 part mixing
product also. It is silicone based which means that it can be a
negative mold and then cast using the same material for the positive.
This is particularly good if you need to make additional negative or
cavity molds. This material is designed primarily to be poured into a
form rather than painted on. But perhaps it has a paintable property to
it. I have also used this product to pour decorative carved wax
candles, so it holds up well to modest melted wax heat. I t also would
be good for making a mold from an existing product, like a metal
medallion. It's quite flexible and forgiving.
Some of the clay art items I make are plaques. They start out as
sculpted masters made from oil base plasticine/plastelene modeling
clay. While I was a designer at General Motors, model makers would
carry hot tubs of this pungent modeling clay and apply it to full sized
styrofoam automobile form to build up the features. When warn it can be
troweled on like thick slip. At room temperature it it firm and can be
modeled with a traditional set of modeling tools. However, if chilled
in the refrigerator it can be shaved and carved like hard cheese.
Modeling clay separates readily from a plaster mold although it is a
lost master method if strident undercuts are part of the design. Clay
caught in undercut cavities come out cleanly using compressed air
rather than damaging the mold by trying to extract the clay using a
dental pick etc. I then carve out any extreme undercuts the plaster
mold may have with dental tools. The result is a piece that looks like
it has undercuts but freely comes out of a plaster mold.
My point is that the RTV silicone casting resin mentioned above would
suit oil-based clay mastering and sculpting methods methods and prevent
loss of the master. Plaster could then be cast around a silicone copy
of the master. The silicone master would pull out of undercuts and not
be damaged.
Dan Saultman
Detroit
To view the plaques I am speaking of visit:
http://www.saultman.com/potfolio.html
On Feb 12, 2005, at 5:56 PM, Randall . wrote:
> I wonder how many here use rubber molds, either in the model
> development process or to cast non-ceramic materials as an adjunct to
> your ceramics...
>
> ...The Polytek mold can be made in a day, it doesn't shrink at all, and
> has a many years storage life, it's forgiving of all kinds of insults
> in making the mold that would kill other two part rubbers to where
> they won't cure, bubble up or otherwise don't work. One brand I tried
> years ago warned that NO moisture of any kind was acceptable in the
> model and that if any was present the rubber would foam up. The
> Polytek like the other two part rubbers is strong but if you get a
> nick say from a blade in a critical spot it can tear, and once it
> starts to tear it tears much easier along the fault line of the tear,
> it's also fairly pricey I buy the kit that is about 2 gallons and
> it's just about $118, but with that size I found I have been able to
> make about 3 medium sized molds or more, maybe 2 larger ones, so it
> works out ok for costs.
>
> Randall
>
>
Craig Clark on tue 15 feb 05
Randall, Dan has given you a very good overview of what you can do
with RTV based molding systems. Additionally, you can also brush the
material onto your pattern, whatever it happens to be. There is a
company in NewJersey that has been in the business for quite a few years
now and has superb technical assistance. They will answer whatever
quesitons that you may have for your specific application directly over
the phone. They have a number of products that work better for various
casting purposes. Here's the link http://www.polytek.com/ I'm
having difficulty with my browser so you will most likely need to cut
and paste. I don't think it is hyperlinked when I mail.
Hope this helps
Craig Dunn Clark
619 East 11 1/2 st
Houston, Texas 77008
(713)861-2083
mudman@hal-pc.org
Randall . on wed 16 feb 05
At 8:20 AM -0600 2/15/05, Craig Clark wrote:
> Randall, Dan has given you a very good overview of what you can do
>with RTV based molding systems. Additionally, you can also brush the
>material onto your pattern, whatever it happens to be. There is a
>company in NewJersey that has been in the business for quite a few years
>now and has superb technical assistance. They will answer whatever
>quesitons that you may have for your specific application directly over
>the phone. They have a number of products that work better for various
>casting purposes. Here's the link http://www.polytek.com/ I'm
>having difficulty with my browser so you will most likely need to cut
Hi Craig,
I think you must have missed a post of mine or something, I ONLY use
Polytek and have for years now, more specifically I presently use
their 74-35 brushable poly. Like all their rubbers, it has nearly no
odor at all.
I always like their newsletter and a few show a HUGE architectural
Corinthian capital they made in fiberglass as replacements for
deteriorated stone ones, the thing was 6 feet tall!
I haven't tried their plastics or resins like Polyoptic clear or
polypoxy for casting as I don't feel plastic or resin is a sculpture
medium- plastic and resin is in my opinion a material that's used for
mass production of cheap products that quickly become brittle or
otherwise deteriorate. It's used for toys that get broken and tossed,
and for garden products you buy at Walmart for $9.95 and stick in the
garden and that usually wind up in the landfill within a few years.
I did once try a polyester resin and bronze powder to make a cold
cast bronze, but it was miserable stuff, sticky, gummy, stunk like an
auto body shop and it wound up costing almost as much in materials as
casting a regular bronze did!
I won't even go into the auto body repainting shop type fumes and
carcinogenic chemicals contained in that kind of stuff, I wouldn't
have it in my house.
Randall
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