2 piece plaster mould


Master Hobbs

This article will show you how to make a two-part mold of an action figure's head from plaster, and make a latex casting from the mold. The same methods apply to making a two-piece silicone mold to be used in resin castings.

To follow along with this article, you will need:
- an action figure
- Super Sculpey or other clay
- Legos
- plaster of paris
- casting latex a.k.a. balloon latex
- petroleum jelly
- rubber bands
- baby powder

The head of your action figure should be sunk halfway into a block of Sculpey. This will be the parting line of the two halves of your mold. Depending on the figure, you may even be able to spot the parting line on the original, and use that for reference. Don't just push it down into the clay, actually smooth the clay right up to the figure; there should be no space between the clay and the figure. Your should also make a few shallow indentations in the clay, to use as registration marks for the two parts of the mold. I used a Lego guy's neck to do this.
The next step is to build a mold box. This will define the size and shape of your mold. I like to use Legos for mold boxes because they make it easy to build, break down, and rebuild a box of any size. You will also need to build a wall of Sculpey at the figure's neck area. Both the mold box and the Sculpey wall should be the same height: about 1/2 inch taller than the highest point on your figure.Brush a thin coat of petroleum jelly onto any part of the figure that will be inside the mold. This will keep the plaster from sticking to your original. (I didn't have any petroleum jelly, so I used hand lotion and it worked OK.) The plaster won't stick to the Sculpey, so just leave that alone.

OK, now the fun part: pouring the plaster. I use plain old hardware store plaster (it's much cheaper than art-store plaster). Mix it up according to the directions, and make sure not to stir any air bubbles into it. While it's nice and soupy, pour it into your box, starting in a corner. Shake or bang the box occasionally to get any stray air bubbles out. Fill your box up to the top, and put it in a dry place to cure.

Now the hard part: waiting. Make sure you wait until the plaster is totally cured before you remove the box and take the figure out, otherwise you will end up breaking off parts of your mold. The plaster should be dry to the touch. OK, now you can take apart your Legos and very carefully remove the figure. Don't snap of the aligning pegs.

Time for the second part of the mold. Now you're going to have the first half of the mold where the Sculpey was before, and flip your figure over to get the back of the head. You know the drill: mold box, retaining wall, petroleum jelly.
This time, you apply the petroleum jelly to the first half of the mold as well. Make sure you get every surface of the mold. Every surface, I tell you! Especially the top and sides of the aligning pegs. If any part of the second half sticks to the first half, you will lose all your work.n).

Also, apply petroleum jelly to the whole head of the figure (not just the back).

Mix and pour the plaster the same way you did for the first half. Wait until it's dry and very carefully ease the parts apart. Ta-daa! You've got a two-part plaster mold! Good job!
Put the two halves together and use a rubber band to make sure they stay together. If you don't have a rubber band, and you're frantically writing an article, tear up an old pair of underwear and use the elastic.
Now to pour the latex. You should be using "casting" or "balloon" latex, which is a very fluid form of latex. This is not Mold Builder latex! (Although maybe that would work, I don't know...) You don't need a mold release when pouring latex into plaster. Take a spoonful of latex and fill the mold up to the top. Slosh it around in there, get all the air bubbles out, and pour the latex out again. This will leave a thin coating of latex inside, which will dry and become a mask. Of course, if you want a solid head of latex, don't pour anything back out.

Now put the mold in a warm, dry place and wait until the latex is dry. For a hollow mask, this will be about an hour. A solid head could be overnight or even a day. When you are ready to remove the casting from the mold, coat your hands and the inside of the mold (if you're making a hollow casting) with baby powder. This will help keep the latex from sticking to itself. Rock the two halves of the mold back and forth to loosen the latex.
Congratulations! You've done it!