Making Molds - Clay and Plaster of Paris

When creating special effects looks its wise to understand the various types of molds that can be formed to create fun and detailed looks.
I started out with a simple clay and plaster of paris type mold. This is a great way to start making molds because it is easy and only requires a few supplies that are easily found at a craft store (or in your dad's shed out back if you are lucky!)

All you really need is clay and plaster of paris. Clay tools are optional, but you can also use odds and ends you find around the house. You can use any kind of clay but I used oil based clay that does not air dry so that I can use it over and over again (also, it was provided to me by my professor). It is also smart to have some kind of mold release. I used peanut oil and baby oil for this, some other options are vaseline/petroleum jelly or spray-type oil 

Gather your supplies and then find a surface that you will sculpt on. You can use anything as long as it has a smooth finish on it, plastic and glass work very well. 

Next, find a source of inspiration for the prosthetic you would like to make. You search for photos on the internet or in books or you could even come up with a sketch for your design. 

For my sculpts I decided to create a knife wound that will ultimately be placed on my arm, a set of warts, and a fantastical diamond-bursting-through-skin  appliance. I sculpted the knife wound using a large water bottle, the warts and diamond on an old binder. 

 I stabilized the bottle with some extra clay underneath. I found a knife-gash photo on Google that I modeled this concept after. I used the bottle to simulate the curvature of an arm as it can be difficult to apply flat-backed appliances to rounded surfaces.

 Above is my wart sculpt. Again I used inspiration from Google images. I textured the warts with one of my pointy clay tools. Lastly I created a diamond shape with skin formed around it so it appears as if it is growing through the skin. 

After the sculpting is complete, build a dam around each sculpture. Make sure it is at least and inch taller than your sculpture and mush it down onto the sculpting surface to get it as air-tight as possible. When this is done, apply a thin coat to the clay surfaces with mold release. Only the surfaces that the plaster will come in contact with are necessary to coat. 

The next step is mixing and pouring the plaster of paris. The ratio of water to plaster of paris varies based on the brand and type of plaster, so be sure to thoroughly read and follow the instructions on the container. When pouring, pour very slowly to avoid any air bubbles that might form. Once poured, pick up your sculpture and tap it against the table a few times to help any air bubbles rise to the surface. 

Once the plaster is dry (I waited overnight to make sure it was dry) you can pull apart your molds. Sometimes they will come out cleanly but if there is any clay left in the mold you can pick it out with a tool or wash it out with water and a toothbrush (for water based clay). I was lucky and two of mine came apart very cleanly, the third only required a small amount of cleaning with a clay tool. 

Now you are ready to use your molds to make some awesome prosthesis! These molds will make an appearance in the coming posts when I talk about how to pour various materials.