Thread: Molding tips

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Hey all,

Having a little trouble with molding and wondering if I could get some feedback.

Here is what I did.

I made a shrunken head out of air dry clay. I then let it dry for about 5 days. To the touch it seemed very hard at this point. I then covered it in vaseline, then tooks some plaster of paris from Michaels (havnt found that 30 cal stuff locally). Gave it a good coat on both sides, using a clay wall as barrier. Let it sit for about an hour and tried to pull it off.

And this is what happened.

When I pulled it apart, first the back of the shrunken head came off in parts. Asuming I may need to do a couple coats here? But when I pulled off the front, it came in one piece, but it also took the nose, part of an ear, mouth, and an eye with it!

So I am kind of at a loss to what I should do here. It seemed that the plaster of paris, either the fact that it was wet or the heat made the clay loose again.

Is it as simple as needing to let it dry alot longer, or maybe I need to find some sort of sealer to apply to the clay sculpture? Im sure the oil based stuff is better for things like this, but really trying to stick to a budget.

Any help would be appreciated. Dont want to keep losing my clay creations!

I don't know that much about molds but you have to use some kind of a release agent...Smear the vaseline in the mold maybe?.....You need something so it doesn't pull it apart to pieces...I wish I was more help but that's my guess what happened....Good luck...ZR

I had always heard that Vaseline was a terrible release agent for plaster. You would probably have better luck with several coats of carnuba wax or a store-bought release agent from Michael's. It may cost a few dollars, but your sane mind is priceless, right??

I think your main issue is that it sounds like you only used one coat of PP. You really need to layer it up thick, as PP is not that durable as a mold. you might even want to add some fiberglass gauze between layers. Ultra Cal 30 is definately the way to go, though. You can find it cheap online, and if you buy smaller quantities the shipping isn't as bad.
As for the clay seperating, yes a better release agent might help, but you have to realize that your original may be distroyed in the molding process. Unfortunately it happens. Just carefully scrape the clay out of your new mold and make as many as many replacements as you want!

I'm not sure what kind of airdry clay you used, but it's possible the vaseline may have softened the clay up a bit.

As for plaster of paris, coats of it REALLY are not going to work for a mold without some reinforcement. The individual layers don't cross-bond well, and bandages won't hold the detail you need.

You should try a method more similar to this:

http://www.opusframing.com/library/pdf/2part_mold.pdf

Then you get two solid blocks of plaster. I'ld say you want at least 1/2" thick on all sides.

good luck, and have fun.

Thanks for all the tips guys! This is giving me some good ideas to work with.

What are your final casts going to be made of? Ultra-cal might not be what you need.

Expanding foam. The stuff you can get in a can down at the hardware store.

Sounds like you are going to need a thin flexible latex or RTV mold for the head and then a strong Hydrostone or ultra-cal mother mold to withstand the expansion. If you any undercuts, a hard cast will not come out of a plaster mold. That is why you might need the flexible mold first.

Ohhh...expandable foam will most likely blow out a PP mold. Definately agree with Scourge. Mother mold with UltraCal.