Creating plastic toys, whether for commercial purposes or your own craft projects, can be done effectively at home using a combination of basic art materials and professional model-making products. The process of making plastic toys begins with a mold, or negative impression of your toy design, which will be filled with your final product material to create an exact copy. For plastic casting, the best mold material is silicone room-temperature-vulcanizing (RTV) rubber, which can be used to create a simple two-part mold.
Preparing Your Materials
Set up your work area for creating molds in a well-ventilated room with a table or other work surface. Cover your work surface with plastic and set your materials within easy reach.
Choose a plastic toy that you would like to copy, or build your own toy design in clay or wood. Coat any soft clay model with a clear sealer and let it dry completely before proceeding.
Lay the plastic toy flat on your work surface. Roll out a sheet of modeling clay that is longer and wider than the plastic toy in this position. Place the toy model on top of the modeling clay sheet.
Build a rectangle of interlocked Legos around the outside of the toy model, leaving at least 1/4 inch between the toy and the Legos on all sides. Make sure that there is no gap between the Legos and the modeling clay.
Add Legos vertically all around your rectangle until you have a height that is at least 1/2 inch taller than the highest point of your toy model. Remove the model from the Lego box you have created.
Pouring the Mold
Mix together half a batch of silicone RTV rubber with its catalyst in a plastic cup, following the specific mixing suggestions for the particular rubber product you have purchased. Pour this batch into the Lego mold box, stopping when the box is halfway filled.
Press the plastic toy model into the silicone rubber until it is half covered. Make sure that the toy is not touching the bottom or sides of the mold. Press several marbles or wooden craft balls into the rubber around the toy in the same manner. Let the rubber sit for 12 hours to cure.
Remove the marbles from the cured rubber, revealing several circular depressions. Mix together the rest of the silicone RTV rubber and pour it into the mold, covering the toy model and filling these depressions. Completely cover the toy. Let the rubber cure for 12 hours again.
Take apart the Lego wall and peel off the modeling clay bottom. Carefully pull the mold halves apart and remove the plastic toy model from the center cavity. Put the mold halves back together, fitting the marble shapes on one side into the depressions on the other side.
Strap the mold together with rubber bands. Cut a small pouring hole into the top or bottom of the mold with the razor blade, reaching the inside cavity.