Recipe 19 : How to Make Silicone Prosthetics in Plaster Molds
- Koji Ohmura
- Feb 3
- 5 min read
When you made prosthetics with gelatin or foam latex, have you ever wondered, what if I created these with silicone? Could it be softer or easier to paint on? Yes, you can run silicone in these molds. I will show you how to run silicone in plaster molds.
If you want to learn how to make silicone prosthetics in flat silicone molds, click the recipe below.
Materials you need...
Petroleum Jelly
Hair Dryer
Chip Brush
Foam Latex Mold Release (Steric Acid from GM Foam)
Urethane Parfilm/ Epoxy Parfilm
Acetone
Baldiez
Airbrush
Compressor
Needle
Respirator
Nitryl Gloves
Scale
Plat Sil Gel 10
Plat Sil Deadner
Revlon Colorstay Foundation
Red Flocking
SilcPig White (Optional)
Mixing Cups
Mixing Sticks
Vacuum Chamber
C-Clamp
RCMA No Color Powder
Material links are here.
Lesson Video
Mold Prep
Before pouring silicone into the plaster mold, we need good mold preparation. Otherwise, silicone prosthetics might stick to the mold and be destroyed.
First, brush petroleum jelly (Vaseline) on both sides of the mold. You can warm it up with a hair dryer. It will create a smoother and thinner layer.
Thin layer of petroleum jelly Next, brush Foam Latex Mold Release. I normally use GM Foam Mold Release. It is stearic acid and creates a nice layer when it dries. If it looks thick when it dries, buff it with a clean chip brush.
Steric acid from GM Foam Do not brush "used" stearic acid from foam latex prosthetics. Sulfur from latex will inhibit platinum silicone from curing.
If you are using a used foam latex mold, paint INHIBIT X from Smooth-On.
Next, spray Urethane Parfilm. Let it sit for 30 minutes. Epoxy Parfilm works as well.
Spray Plastic Skin
Gel 10 Silicone stays sticky if there is no plastic skin. So, you will need to encapsulate the silicone prosthetic with plastic skin on both sides. I use Baldiez for this. It is acetone-based. You can use Super Baldiez, which is alcohol-based, if you like. It is softer but also more fragile.
Baldiez normally comes in a thick liquid. You need to thin it out with acetone in order to spray with an airbrush. My favorite ratio is 5:1 (Acetone:Baldiez).
Pour this into the airbrush cup. Keep the leftover mix in an airtight, acetone-resistant container.
Spray 2 layers of Baldiez on both negative and positive mold. Each layer needs to dry before the next layer.
Spray Baldiez all around. 3rd layer is on the sculpture edges only. Too much Baldiez layer will make the surface stiffer. Use a needle and pick the plastic skin on the outside of the prosthetics. Check if it looks like a spider web or pantyhose. If it looks like a plastic wrap, it is too thick.
Checking the thickness of Baldiez.
Mix Silicone Base Color
PlatSil Gel 10 is a standard for silicone prosthetic makeup now. It comes with A & B. Mixing ratio is 1:1. For this prosthetic, I am making it 150% soft. It is very easy to handle during the application. You might adjust the softness accordingly. I tried other softness levels for some facial areas. The softest one was 200%. It was very soft and moved well. I just needed to hold it carefully when I applied it.
When you mix it, it is important to weigh out the exact amount of each. You will need some math skills here.
Mixing silicone color with Revlon Colorstay. Formula for 150% softness
Platsil Gel 10 A - 100 grams
Deadner - 300 grams
Revlon Colorstay Foundation - 3 grams
SilcPig White - 0.6 grams (Optional)
Red Flocking - 0.06 grams
Calculation example (Do not mix these! It is just a calculation to figure out how much deadner you will need for 150% softness.)
A = 100 grams
B = 100 grams
A + B = 200 grams
200 x 1.5 (150%) = 300 grams
Deadner = 300 grams
Once the tinted mixture is ready, I put it aside. Then, I take an adequate amount from the cup. This time, I only used 100 grams. I added 25 grams of B. This is how I calculated it. (D is Deadner.)
Here is a cheat sheet.
150%: (A + D) divide by 4
175%: (A + D) divide by 4.5
200%: (A + D) divide by 5
Example; B = 100/4 = 25
Mix it thoroughly.
Mix Silicone A & B
Mix A+D and B together and place it in a vacuum chamber to remove bubbles. I leave it in the chamber for 1 minute. If you do not have a vacuum chamber, pour the silicone from a high point slowly.
Popping bubbles in a vacuum chamber. Pour the silicone onto the mold. I pour on the edge of the sculpture area first. You can put a wooden piece or clay under the mold to level it, and pour the rest onto the positive mold.
Pour it on both sides. Check if there are no bubbles and close the mold. Use the keys to guide the mold to lock in. Then place 2x4 wood and a mold strap to tighten the mold.
Don't move it while it's curing.
Opening the Mold
2 hours later, check the silicone leftover on the side of the mold if it is cured.
Add RCMA No Color Powder from the side. Using a hair powder atomizer is a good idea. Some people do not put powder on in order to keep Baldiez skin clear. If so, remove it carefully.
Pumping powder with an atomizer. Use three pieces of 2x4 wood to make a bridge. Hook a C-clamp onto the bar of a positive mold and the bridge.
Twist the C-clamp and open the mold slowly.
2x4 bridge and a clamp As it opens, keep the prosthetic only on one side of the mold. In this process, I kept it on the positive mold.
Powder on the prosthetic and remove gently from the mold.
Powder on the prosthetic.
(Optional) Wash the Prosthetic
I like a less powdery look. So I normally wash the prosthetic with water. Since the edge is very fragile, I only use a water spray, not running water. When I apply the prosthetic on a model, I wipe it again with Windex or 70% alcohol.
Since this piece is a unicorn forehead piece, I punched hair to make it look like a horse mane. You can watch this video to learn how to punch hair.
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