Step 3: Mixing Oogoo
As stated before, Oogoo is simply a mixture of clear silicone caulk and corn starch. It can be mixed anywhere from 5 to 1 to 1 to 2 silicone to corn starch by volume. Up to a point, the more corn starch you add the faster it will set up. I like to mix it in small disposable cups using a Popsicle stick that is wrapped with Gorilla Tape to create a spatula. See pic4. Once it cures the Oogoo peels easily off the tape wrapped stick and the mixing/spreading stick can be reused.
Mix In Small Amounts
A good starting mixture to try out is 1 corn starch to 1 silicone by volume. It is easiest to mix it in small quantities so as to have plenty of time to work it. To see how it works, you could start with 1 tablespoon silicone caulk to 1 tablespoon of corn starch. You can reduce the amount to as little as 1/4 tablespoon corn starch to 1 tablespoon silicone if you want more time to cast it or sculpt it. I rarely mix up more than 3 tablespoons of silicone at a time.
The dry starch and sticky silicone do not want to easily mix. But if you are persistent and keep quickly stirring and mashing the mix, they will eventually merge into a thick paste. The resulting Oogoo is very sticky and will stick to anything that you spread it on. Most things it will stay well glued to. On a few things like some plastics and metals, it will easily peel off after it has cured.
The resulting Oogoo is a nice reflective white but I recommend coloring it so that you can easily see if you have an even mix. See the coloring step.
WARNING: While mixing, Oogoo will give off the strong smell of Acetic acid which can be irritating to the eyes and respiratory system. I strongly recommend that the mixing and forming be done outside or in a VERY WELL VENTILATED room. You should also wear nitrile gloves while mixing as the uncured silicone contains other solvents that might be absorbed by the skin.
One recurrent problem with silicone caulk is that once opened, it will tend to set up in the tube tip. To get a good seal I have had good luck using Gorilla tape wrapped over the tip. See pic4b. If you leave a quarter inch gap between the wrapped tape and the tip you can squeeze out just enough silicone to seal the tip well from air and moisture.