question on molding/vacuum forming a clay sculpt

takevin

takevin

Sr Member
ok, i have my chewie underskull sculpted in oil based clay. In order to work with this clay, it has to be warmed up to work with it. Now I would like to vacuum form over this, but with the heated plastic, it would damage the sculpt. What do you think if I were to put the sculpt in the freezer overnight or for a few hours and then vacuum form it? Or, use plaster of paris to mold the sculpt, then I can pour a two part resin in the plaster of paris mold. If I use a release agent the oil based clay should pop out of the plaster of paris correct?? Input please?
 
Actually, I do this with water-clay all the time without a problem. Yes, you can do it with oil clay. Putting it in the fridge will make it pretty solid for vac'ng. You will get 1 good pull, but might have to re-smooth the clay afterwards.
 
One issue: I did this as well with the cheapy cheap clay, and it worked BUT what happened when the cold clay hit the hot plastic was MASSIVE cooling reaction. Cooling lines all over the place, as the plastic tends to buckle when it comes into contact with something cold. Both the vac form and the mold were changed....ruined really.
You might go with the plaster idea, much less likely to ruin the sculpt.
 
I've thought about trying to find a better way to mold a clay sculpture without using silicone or other expensive material. You may want to try an idea that I had about a month ago--buy some alginate, and basically make a "lifecast" of your sculpture. It's cheaper than silicone, and you can pour one or multiple plaster casts of your sculpt without worrying about vac'ing over your sculpt--as long as you pour multiples one behind the other before the alginate shrinks.

If you try it, let me know how it works, as I've yet to get to the point where I can try it.
 
Similar to LordVdr's idea, you could make a brush-up mold out of latex or urethane (you would also need to make a mother mold to help it hold it's shape - I would recommend plaster bandages since they are fairly cheap and easy to use) and then cast an ultracal buck from that. That way you can use the mold in the future if you ever need to make additional copies.

Randy
 
I've read that it works to vacuum form very thin plastic over a clay sculpt and leave it on. Then vacuum form (somewhat) thicker plastic over that. The thin plastic shell stabilizes the surface of the clay and keeps it from getting quite so hot quite so fast.

(Maybe a lot less hot, if heat doesn't come through the thick plastic any faster than it conducts away through the clay.)

I wouldn't try that for the first time on a sculpt I really cared about, though.

(I'd be leery of doing it at all, in case the first pull of thin plastic went wrong. You'd likely wreck the sculpt trying to get it off to do it again. But then, I'm a risk-averse type.)

Making an alginate mold and plaster cast seems much safer.
 
If you want 1, vac form over clay.

If you want many and have few $$$ here is a cheep way.

Make a quick plaster mold of your part. As soon as it's set add mold release. Vasileen is cheep and always works. Poor more plaster into your mold and make a positive part.

Vac-form as many as you like.

You can keep mold around to make new positives if you need but it'll shrink with age. Days can make a difference.

BrianM
 
BrianM said:
Make a quick plaster mold of your part. As soon as it's set add mold release. Vasileen is cheep and always works. Poor more plaster into your mold and make a positive part.
Click to expand...

Oily release agents like petroleum jelly (Vaseline) tend to dissolve modeling clay at the surface. That messes op the surface and tends to make it hard to get out (there's a gooey vacuum there).

Alginate makes it easier to get a clay sculpt out without messing it up. It doesn't stick to modeling clay, so you don't need a mold release.

(And alginate sets up fine on cheap sulfurous modeling clay. It's not inhibited by sulfur like silicone. I use ultra-cheap modeling clay from the dollar store and it works great.)

Here's an example, using alginate both for face lifecast, and then to mold a sculpt built on that lifecast. (The we cast a vacuum forming buck from water putty, and formed craft foam over it.)

http://www.tk560.com/phpBB2/viewtopic.php?t=635
 
Is it possible to make a sculpt from regular brown clay, to then let it air dry until it's hard and to then vacuum form plastic over it?
It really necessary to make a plaster positive if you don't NEED to use the mold again?
 
Varya said:
Is it possible to make a sculpt from regular brown clay, to then let it air dry until it's hard and to then vacuum form plastic over it?
It really necessary to make a plaster positive if you don't NEED to use the mold again?
Click to expand...


This thread was from 2007. It's generally not a good idea to revive a long dead thread.


However, in my experience vacuum forming, you will always NEED to use the mold more than once. If you think you're going to get it on your very first try, you'll probably have a very rude awakening. Every buck I've pulled from took learning. Where does it draw? Where does it not draw? Will there be webbing? Etc.

It is much easier and safer to mold and pull a plaster positive.
 
I second the post above me; you're definitely gonna do it more than once, especially if it's your first go. When I started out, I had a sheet of 4x8' PETG that I plowed through in on setting just to get one good pull.
 
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