How the Process Works

There are a million different ways to mold plastics. One of the simplest is to cast a positive item in a harmless degradable casting material, and then form identical positives from the negative mold.

To begin this process, one must select an object capable of being casted in this way. For something to be castable in this way, the surface of the object really only needs to have minimal "undercuts". An undercut is a section of the surface where the material turns in from the surface, and then turns under. If there are undercuts that are over an 1/8" approximately, when you remove the object from the mold, the casting material will get stuck under the surface of the object and tear. If you want to cast an object with an undercut, you can place a small amount of molding (non-drying) clay to cover the orifice.

To do a simple 2D mold, start by making a mold box. Scrap foam-core works best for this. Construct a 5-sided box out of the foam core, about 1 inch larger than the item you are trying to mold. Use Hot Glue to make the seams water-tight. Affix the item to the bottom of the box, if possible. If not, a way of suspending the item in the mold will be necessary.

To do a simple single-use mold, an algae-based mold making materials. This is also skin-safe. More durable molds can be made out of silicone rubbers. Mix the material according to package instructions. Fill the mold box with the liquid material 3/4 full. Suspend the item in the mold if necessary. To make a 3D mold, use pencils or other cylindrical objects and place 3 or 4 surrounding the object, being careful not to interfere with the mold. Let the material dry, according to package directions.

Once dry, carefully remove the mold box. To make a 3D mold, leave the object inside the mold you have already made. Remove the cylindrical objects. Make a new mold box that will contain the mold you made, the object, and then space to make another mold of the other side. Repeat the process.

Carefully remove the master object, and mold parts, and any other extraneous bits and bobs used in the mold making process. If making a 3D mold, stand the mold halves upright, and carefully cut a hole to the base of the object you are casting. This will allow you to pour the plastic into your mold. Spray the inside of your mold or mold halves with a release agent. Then place a piece of foam core on either side of the mold, parallel to the split in the mold and rubber band it together with as many rubber bands as you can find. The foam core will keep the rubber bands from slicing your casting material in half, but the rubber bands need to apply enough pressure to keep the split in your mold water tight. 

Mix the ABS (or preferred casting material) according to the package directions, and slowly pour into the molds. Gently shake the molds to remove air bubbles. Let set per package directions. Gently peel out of the mold to make a plastic replica of an object.