RE: Silicon molding help needed

From: Scott Nelson (
Date: Fri Dec 12 2003 - 15:48:55 EET


I have a lot of experience with this (but it was a while ago so my memory is
getting foggy)

Sulpher is correct, sculpture supply houses sell sulpher free plastacine.
PVA is a green liquid you brush on - think of it like liquid green garbage
bag. It creates a great seal on 'certain' materials, very thin.

Even thinner, and this is where my memory is dim, is an epoxy with the same
viscosity as water, with a really long cure time that I used to use. No
way can I remember the name though....

If you use a spray on mold release, make brush it out with a fine brush to
break up any carrier solvent on the surface then leave it for 20 min to
allow the carrier solvent to evaporate.

And my last tip: prepare a small sample part you don't care about in the
same material, and try it first! Before you throw out hundreds of dollars
of resin (speaking from experience!)


-----Original Message-----
From: [] On Behalf
Of Deanda, Jerrold
Sent: Wednesday, December 10, 2003 7:44 PM
To: 'Bathsheba Grossman';
Subject: RE: Silicon molding help needed

Ah Bathsheba, you are a hot dog....yup, that's what I remember, now you say
it. Thanks for the memory jog.


-----Original Message-----
From: [] On Behalf
Of Bathsheba Grossman
Sent: Wednesday, December 10, 2003 3:18 PM
Subject: RE: Silicon molding help needed

On Wed, 10 Dec 2003, Deanda, Jerrold wrote:
> We do a bit of silicon rubber molding and the only time we've had
> trouble with surfaces not curing was when we used modeling clay to
> fill out the parting line around the master. The toy store clay has
> something in it (I can't remember the exact material) that inhibits
> the material from curing on the surface against the clay.

I thought it was the sulfur in the plasticene that caused this?

> My choices to try would be the PTM&W mold release, (no measurable
> buildup if you need an accurate part) or good ol' vaseline... It's
> surprising how well this old stuff works. You can put it on real thin
> and wipe it off until you can just barely see it on there. Works
> better than some of the exotic (read: expensive) special mold releases
> sometimes.

Score another vote for vaseline -- so low-tech I didn't wanna mention it,
but it works good.


Bathsheba Grossman                 phone (831)429-8224, fax (831)460-1242
Sculpting geometry                                
Solidscape prototyping                           
Protein crystals                             

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