Things You'll Need
Silicone rubber kit
Whether you need a theater prop or a Halloween decoration, you can create your own brain mold using liquid silicone. This silicone comes in a pair of bottles that, when mixed together, harden into a flexible rubbery mold over an object. Companies produce many different kinds of liquid silicone, each one suited to a different purpose. If you wish to make a brain-shaped jello mold, for example, you will need food-grade liquid silicone.
Lay out three layers of newspaper over your work area. Make sure your workspace is in a well ventilated area. Place a plastic container such as you would store food in on the papered workspace. Make sure your container is large enough to comfortably hold your prototype with at least an inch to spare on all sides.
Half fill the container with plasticine. Pack it down and smooth the surface over with your fingers. Embed your prototype brain half way into the plasticine.
Embed four marbles in the corners of the plasticine. Place a drinking straw on the plasticine bed, with one tip touching your prototype and the other the wall of the container.
Paint liquid wax over the inside wall of the container and over your prototype. Liquid wax will keep the silicone from adhering to the container and the brain.
Don gloves and a respirator. Take the two bottles of chemicals from your liquid silicone kit and pour them into two separate mixing cups. The total amount should be enough fill the remaining space in the plastic container. Most silicones use a 1:1 ratio between their chemicals, but some silicones require more of one chemical than the other. Check the packaging.
Pour the two cups of chemicals into a third cup and stir it with a mixing stick for one full minute. Then pour the mixture into the plastic container. Allow it to cure for 24 hours. You now have the first half of a two-piece brain mold.
Turn the container upside down and tap on the bottom of it until the contents come free. Shake it if you need to. Once the contents are dislodged, peel the plasticine away from the bottom of your mold to expose the other side of the prototype.
Place the prototype, silicone-side down, back into the container. Remove the marbles, but leave the straw and the prototype in place. Paint the newly exposed face of the prototype, the mold, and the walls of the container with liquid wax.
Mix up a second batch of liquid silicone in exactly the same way as you did the first batch and pour it into the plastic container. Let it cure for 24 hours.
Turn the container upside down and tap on the bottom to dislodge your mold. Peel the two halves of the mold gently away from the prototype. Rinse them under water to remove any residual wax.
You can find fake brains at Halloween stores or from biological classroom supply companies. These work well as prototypes.
Avoid breathing in the silicone fumes or having skin contact with the liquid silicone. Keep it away from animals and children.