Debbie on thu 18 jul 02
Hello Steve,
If your oil clay has sulfur as an ingredient in it, then that will react
with the RTV (silicon) and prevent it from curing. For this reason I use
only non-sulfur plasticenes. You can however use a barrier on your oil clay
such as lacquer or shellac and then you RTV should set up fine, but it's
always good to run a little material compatibility test fist. It certainly
is a mess trying to clean off uncured RTV from a delicate plasticene model.
Also, a very small inaccuracy in weighing out the catalyst can cause the RTV
not to cure. Good luck! Debbie
> -----Original Message-----
> From: Ceramic Arts Discussion List [mailto:CLAYART@LSV.CERAMICS.ORG]On
> Behalf Of Steve Hammond,Terrasculpt Designs
> Sent: Thursday, July 18, 2002 7:59 AM
> To: CLAYART@LSV.CERAMICS.ORG
> Subject: Question - silicon molds and Roma Plastinlina Clay
>
>
> We have relatively simple clay bas-relief made from
>
> Roma Plastinlina clay #3 Medium Firm. This is an oil based clay
>
> We want to make a silicone mold but have been having trouble
> getting the silicone to harden.
>
> QUESTION: WHAT MATERIAL SHOULD WE USE TO FORM A BARRIER SO THE
> SILICONE WILL HARDEN?
>
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Steve Hammond,Terrasculpt Designs on thu 18 jul 02
We have relatively simple clay bas-relief made from=20
Roma Plastinlina clay #3 Medium Firm. This is an oil based clay
We want to make a silicone mold but have been having trouble getting the =
silicone to harden. =20
QUESTION: WHAT MATERIAL SHOULD WE USE TO FORM A BARRIER SO THE SILICONE =
WILL HARDEN?
John Weber on fri 19 jul 02
Maybe someone else will give you an answer but if not you may want to check
out these web sites on rubber molds for more information.
http://www.polytek.com/index.php3
http://www.sculpt.com/
http://www.mouldmaking.freeserve.co.uk/index.html
Suzanne Tourtillott on fri 19 jul 02
If you're using a two-part silicon compound, you must have equal portions of
each, and knead them very thoroughly until no streaks (from the two
different
colors of the compound) are visible. Your query asks for a recommendation on
a barrier that will cause the compound to harden. To my knowledge, the
barrier has nothing to do with the compound's ability to harden.
According to (ceramic) mold maker Tom Spleth, Murphy's Oil Soap (undiluted)
works well for plaster-mold release, but I believe that no barrier is
necessary for a silicon mold; it's slick enough as is. Please check this out
with a potter, though. My info comes from what I've learned from jewelry
makers who use silicon molds.
Snail Scott on fri 19 jul 02
At 07:59 AM 7/18/02 -0700, you wrote:
>We have relatively simple clay bas-relief made from
>Roma Plastinlina clay #3 Medium Firm. This is an oil based clay
>We want to make a silicone mold but have been having trouble getting the
silicone to harden.
>QUESTION: WHAT MATERIAL SHOULD WE USE TO FORM A BARRIER SO THE SILICONE
WILL HARDEN?
NEVER use Roma plastilina for making rubber molds. The
sulfur in the clay reacts with both silicone and urethane,
preventing either of them form setting properly. If you
must use a sulfur-containing plasticine, spray it WELL
with shellac. If the piece has any undercuts where spray
shellac might not reach, apply it with a brush to those
areas. Then apply a silicone parting compound and let it
dry before applying the rubber. In the future, choose a
non-sulfur plasticine to sculpt your pattern. Chavant
makes several varieties of good sulfur-free plasticine
clays. It can be purchased from sculpture-supply houses
and directly from the manufacturer. VanAken clays are
also sulfur-free and widely available in many hobby and
craft shops, though only made in one grade of firmness
(soft).
-Snail
Rob House on fri 19 jul 02
On Thu, 18 Jul 2002 07:59:08 -0700, Steve Hammond,Terrasculpt Designs
wrote:
>We have relatively simple clay bas-relief made from
>
>Roma Plastinlina clay #3 Medium Firm. This is an oil based clay
>
>We want to make a silicone mold but have been having trouble getting the
silicone to harden.
>
>QUESTION: WHAT MATERIAL SHOULD WE USE TO FORM A BARRIER SO THE SILICONE
WILL HARDEN?
STEVE -
What kind of silicone are you using?
Tube of Caulk ? or Liquid with hardener?
If you've got liquid silicone + hardener and it doesn't cure, perhaps it
isn't being mixed in the right ratio. Or maybe it's old = bad chemistry.
A tube of silicone caulk and a finger can make an OK mold of an appropriate
object (fist size or smaller).
MOLD REALEASE can be purchased, probably where the silicone was purchased.
spray it over the original + allow to dry.
PAM kitchen spray = poor man's mold release.
Pour the Silicone over the top of the draughtable original.
Silicone molds are pretty flexible when they are thin, but if too thick
they can still be troublesome to remove.
Well Enjoy - -- Rob House
www.robhouse.com
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