By the way, this is my first Instructable so if you find it interesting, I would truely appreciate any comments.
Step 1: Gather Materials
~Object to make a mold from
~Mold compound - in our case we will use liquid latex
~Plaster cloth - used to make a frame for our latex mold
~A clean, Taclon brush. - used to "paint" on the latex. Dont use a regular paint brush. Ill explain later.
~Clay - used to make a base for the mold
~Plastic food wrap
Step 2: Preparing the Object to Be Casted
First thing, take your clay and make a flat base, about an inch wider than the bone. Next build clay up around the bone until there are no gaps between the bone and the clay base you made.
The picture below was taken days after I made my mold, so the clay dried up and receded. You really dont want a gap because it causes problems when you go to de-mold.
Step 3: Apply the Latex
Here is a good tip. Don't use a regular paintbrush with the hair like bristles. Instead use the brushes that have the plastic bristles.
Step 4: Make a Frame for Your Mold
So after you have applied all of your layers of latex, and they have dried throughly, your going to wrap your mold in clear food warp. The frame itself will be made of plaster cloth, the clear wrap just makes the frame removal easy and clean.
Now you dont the warp or plaster cloth to be tight on the latex. The clear wrap should loosely hug the jaw, but the plaster cloth should kind of blanket the bone. In other words, the Cloth is going to harden, and if it curves around the bone, your not going to be able to get it off. It needs to be able to be pulled up without catching on any thing.
(ugg hard to explain but once you do it you'll under stand)
Step 5: Making Sure Every Thing Worked
Once you get the frame off, peel off the clear wrap. Then gently pull off the latex mold. Dont worry about stretching it out. Latex can be stretched pretty far if you put on enough coats.
Step 6: Actually Making a Cast
Now pour in your casting material. For this instructable I will be using plaster. One its cheap, two its easy to mix. Also plaster drys enough to be removed from the mold in about an hour. The downside with plaster is that it chips easy and does not hold up to moisture at all. After I make something I spray it with a weather resistant paint to prevent it from melting if it gets wet.
After the plaster has set up for an hour, peel off the mold just as you did off of the original. Below is the final product.
Step 7: Oh Yeah!
If you dust the latex mold with talcum powder or regular baby powder, it will prevent the latex mold from sticking to itself.
I totally forgot something until "Dramatic Imagery" reminded me. Before you start coating your base model with the latex, you can coat it in a release agent that will help with keeping the mold from sticking to everything. You can buy some commercial stuff or do as he says and coat it with talcum or baby powder. Also, after you make you mold, coat the inside so when you make your cast they wont stick.