Question on making a urethane mold of a sculpey sculpture

Hey folks!

I was sculpting previously in Roma Plastilina, then creating urethane molds (I'm using Smooth-On's Brush-On 35) for them to do plaster casting from. I just tried out and LOVED Super Sculpey. I LOVE having a non-squishable master!

Anyway, my question is: Does anyone know if cured Super Sculpey needs to be sealed before applying the urethane mold material? (Sealing is important if the model is either porous, or is reactive with the urethane, as is the sulfur in Plastilina, for ex.). (BTW, I will be applying a silicone release agent regardless.)

Thanks very much,

Hi - no super sculpey do NOT require any type of seal. It is a hardened surface already.

Het Cat Just what are Sculpey and Fimo and the others really made of anyway? You should not have been able to get urethane to cure touching Roma, it's a problem we often mention. Usually shellac is suggested as a barrier, or PVA. You should be doing little experiments there. I would use thinned Vaseline or Sonite Seal Release on the S. Sculpey.

Sculpey and Fimo are said to be made of 'polymer', which is a vague, catch-all term for plastic. Beyond that, I'm not sure.

And you're right, like I said, Roma Plastilina contains sulfur which inhibits polymerization, so you have to seal first with shellac or whatever.

I was really trying to find someone who actually has experience with this combination of materials. I asked at Smooth-On's tech help line, and got a 'Um, SHOULD be OK...' So I was just hoping to find someone who knew!

With all due respect, do you know that this works from trying it? The issue is more if the surface is porous, regardless of how hard it is.

With all due respect, why don't you do a test run yourself? If you're in doubt just use a mold release and stop sweating it. Polymer clays are made of the same stuff they make those white plastic plumbing pipes out of.

Hey Dan, What's Sonite like? Always wanted to try that product, is it good for a piece of antique, irreplacable sandstone carving for example. I have used multiple coats of clear PVA because I can wash it out after - is Sonite fairly unnoticeable?

Hey Debra,

I appreciate your trying to help (I'm hoping here that my reading of sarcasm in your reply is mistaken), but really, I'm trying to find an answer to a very specific question that frankly requires a more in- depth understanding of both urethane rubbers and polymer clay than either of us seem to have.

I appreciate your suggestions, but just to clarify for others who might be reading this, applying a mold release is NOT a substitute for a sealant. I agree that both polymer clay and PVC pipe are made of plastic, but there are many different formulations of plastics, which can have quite different properties

Yes, I've done it several times. A mold release is more than enough. A small test sample would bear that out. That said, I find silicone a far better material for this purpose.

Thanks for the info. I'm glad to know I'm doing the right thing.

Hi Gary Sonite seal release is a grease, so it will darken anything porous. It has a smell I like, but wouldn't want to eat off it. You might wash it off the stone with a solvent but I wouldn't go there. I might use their Universal Mold Release which is a silicone I think.