Best Clay to use?

What is the best type/brand of clay to use when making a mold for vacuum forming? and what is the best type of plaster to use, too? How do you harden the clay? Thanks for the help.

 

Your question is kind of confusing. You don't use the clay to make the mold, you use it to sculpt your part. And if you're going to make a mold of it, why would you need to harden the clay?

All you need when vacuum forming is a hard copy of the part you're making. Most people sculpt the part in an oil-based clay, then make a mold from plaster, and then make a final casting in plaster. Two things to remember when doing it this way: 1) If you want to keep your mold intact, you can't have ANY undercuts, and 2) If this will be the only copy you're making, there can be some undercuts, but you'll have to break the mold to get the part out.

As far as clays go, anything oil-based will work fine. The largest brand name I know of is Roma Plasticina, which comes in varying hardnesses, depending on your preference. And for something like vacuum forming, plaster of paris or a molding plaster will be all you need.

 

i thought that the clay had to be hard to put the plaster on and then take the plaster and cast plaster inside of the mold and you get the same shape as the clay. I figured it had to be hard so that the clay doesnt change shape while putting on the plaster.

So let me get this right... All you have to do is sculpt the clay into the shape you want, put plaster on it to get the negative, then pour plaster inside of that. Then seperate the two plasters and you will then have the mold. then put that on the forming table and TADA you have what you want. Is that what it is?

Thanks

 

Yeah but you've got the terminology backwards. The negative IS the mold. The positive plaster copy is a casting. Unless you mean it's the "mold" for the plastic casting.

Oil based clay softens when it's warm, but at room temperature it's pretty firm, depending on what kind you're using, so it won't deform when you're making a mold of it.

But yeah, you've pretty much got it. Except you didn't say anything about a mold release. Which is essential. Don't forget about it.

 

yeah like vasoline or something. THanks a lot for the help!