Once you have started sci-fi scratch-building, you will always look for more effective ways to produce or re-produce parts and details. Molding and casting is one way to build better and faster models.
Imagine that you have worked for several hours to make one particular detail and that this exact part is used ten times on the model in other places. Scratching ten identical parts will be difficult, time consuming, and boring. With molding and casting this will be fun, fast, and even educational. This method will produce exact copies of your prototype and as many as you need.
The first thing you need to do is to buy the right materials. You will need two different types:
- RTV silicone for the mold
- Resin casting material
The molds must be made from a special kind of industrial silicone called RTV (Room Temperature Vulcanizing). These silicones are very expensive! If your local hobby retailer doesn’t carry it, try looking in the yellow pages or on the internet.
Be sure to specify what kind of casting material you will use because there are many available. The types are:
- Polyurethane – yellow color (recommended)
- Polyester – yellow color
- Epoxy – clear, white or gray color
These materials are based on two or more chemical components and come in many different qualities. You’ll need a resin that has a pot-life (the working time from you mix the components until the resin starts to thicken) that is approximately 5 to 10 minutes. This is the time you will need to mix and pour the resin. If the mold is large or has a lot of “hard to fill” details, you must consider a longer pot-life. The longer the pot-life is, the longer the curing time will be (the time it takes to cure into solid resin). When resins cure they develop a lot of heat because of the chemical reaction in the material. This is normal, but remember that the resin will cure faster if the room is warm and slower in a cold room.
Resins also have different consistencies. Some are thick (good for massive molds without many details), while some are thin (good for smaller molds with a lot of details).
Both urethanes and epoxies can be pre-colored with a special araldite color. This will not affect the quality of the product if mixed in the right amounts. I prefer to mix some white and black into the resin. This will make the cast parts gray and it will be easier to spot faults like bubbles and so on.
To sum up, the following are important when buying resins:
- Curing time
Warning! I don’t want to scare you, but it would be irresponsible of me not to mention the health hazards involved when working with these materials. Please note that all these materials and their gasses are harmful to swallow or breathe. They can also cause serious allergic reactions. Epoxies can be lethal to those that are allergic and getting hardener in your eyes will probably make you go blind. Use vinyl gloves, eye protection and proper ventilation!