A mold is defined as a negative form that is used to shape casting materials. This allows individuals to create duplicates of the original object. The cast will have the precise likeness but in a hollowed mold form. Below is a quick and intuitive guide for making your own mold and casting.
Materials Needed for Molding and Casting
To generate a mold, you will need your preferred 2 part rubber be it silicone or urethane. There is a variety of casting materials available and the one chosen will depend on what you are molding. In general they consist of an activator/hardener that cures near room temperature in approximately 24-48 hours. In addition you will also need a master model of the object you wish to reproduce.
Lay Out the Dividing Plane
The dividing plane must be laid out prior to producing the dual part mold. This can be accomplished by pushing a master model inside the modeling clay until it reaches the desired dividing plane (it does not need to be perfectly horizontal). Additionally, registration keys are needed to correctly align each mold half. This prevents any issues with both halves coming together which would allow casting material to leak out running your part.
These keys could be something as simple as the handle of a brush or carved grooves. Any object capable of disrupting a smooth surface can cause the slipping of the mold halves. An external shell will then be used to hold liquid silicone and avoid accidental slippage.
The internal space (walls within the shell), master model, and modeling clay surface must be covered with the mold-based release agent. If this is not done, it becomes difficult to extract the master model from its mold later on.
Creating the Mold’s Lower Half
Pour the silicone mixture with a combined activator inside the shell’s corner. Consider using an adequate height of about ten centimeters in order to remove as many air bubbles as possible created by the mixing process. Allow the silicone to spread and then fill in every area of the shell. Ensure that the silicone cures properly before removing its lower half. Once separated you can clean off any excess modeling clay carefully in order to prepare the mold for the other side..
Once the master mold is clean, it can be covered using a release agent if necessary and used to produce subsequent castings. Doing this prevents your casting material from sticking to the mold thus ruining your ability to produce more.
Working with the Casting Material
The casting material must be poured inside your mold using a pouring channel if possible. The size is essential to produce a quality casting (with the exception of centrifugal casting techniques). For most materials except metal, it must be between three and five centimeters in length. Wax, concrete, or plaster requires an allowance of about three centimeters. Cut a minimum of 1 air vent to allow air to escape the model faster. The vent, however, must be positioned above the spot where the pouring channel comes into contact with the model cavity.
