Things You'll Need
Clear coloring agent
Silicone casting agent
Object to be cast
Plastic is a convenient material with which to make small objects for art, craft and household uses. It can be molded with silicone and many other materials, which makes it quite a flexible medium. The only difference between clear plastic and any other sort is the coloring agent. Use a clear coloring agent and make sure to not contaminate the plastic with any dirt and detritus to get a clean, transparent piece.
Decide on the type of mold you want to use. There are dozens of different ways to mold clear plastic. One of the easiest ways to do it is to use a silicone mold making compound, such as the one linked to below in Resources.
Pour enough mold making compound to cover the object you want to mold into a plastic container. In the case of the mold making compound below, you will have to mix equal proportions of both bottles first to activate the silicone.
Immerse the object in the mold making compound and wait for it to set. Different compounds have different setting times, so follow the instructions on the compound you are using. Once it does set, pull the object out.
Measure your mold. Pour water or sand in it, then pour the liquid into a measuring cup or graduated cylinder. The amount that fits in is how much plastic you need to mix.
Mix your plastic. A typical plastic will have resin, a catalyst and a coloring agent. To mold clear plastic, use a clear coloring agent. Depending on the plastic, you will have to use different proportions of the different chemicals. Mix it thoroughly in a paper cup with a stir stick, since residue from the plastic could ruin a bowl.
Pour the plastic into the mold. Ensure the mold is level and stable. Leave it to dry at room temperature in a dry room where it will not be disturbed overnight.
Remove the clear plastic from the mold. Since the plastic shrinks a bit during the process, you will probably be able to get it out just by turning the mold upside down and tapping it lightly on the counter.
Mix the plastic thoroughly before pouring it. Start with a simple object. More complex shapes are harder to mold well.
Don't use too much catalyst. It can heat the plastic too much during curing, or result in it not setting up properly.