Mold Making
There are many different materials available to help you make molds for general use. You can go to your local arts and crafts store, or check out some of the online art supply houses. Some of the products used for general moldmaking are: gelatin, wax, urethane rubber, and silicone rubber. Gelatin, or jello, is any easy and inexpensive way to make molds. Just make it into a liquid, put the model object into it, and let it harden. The same is for wax, except that wax is good because it can also be painted on the model. Both gelatin and wax can be melted and reused.
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Both urethane and silicone rubber mold making systems come in two parts. One part is the rubber and the other is a curing agent, or hardener. The general steps to using them are:
- Prepare the model and set-up mold forms.
- Spray a mold release agent over the model and forms.
- Prepare the moldmaking mixture according to the manufacturers specifications.
- Remove air bubbles from the rubber mixture.
- Paint or pour the moldmaking mixture over the model.
- Let the rubber harden or cure according to the manufacturers specifications.
- Remove the model and forms from the mold and trim as necessary.
When deciding on which urethane rubber or silicone rubber product to purchase you will normally be given a choice of durometers, which means how hard or flexible the mold will be once it has cured. They will usually range from soft, medium, or hard. Soft molds are easy to demold, and can handle deep undercuts. Whereas, hard molds can handle less detail, but will last alot longer and can be reused over and over without fear of breakage. Medium lies in between. Another choice is thixotropic molding products. Thixotropic moldmaking products are very thick and won't run in an uncured state. It is applied with a brush or trowel.
One thing you must pay very close attention to is the gel time and demold times listed for urethane and silicone rubber moldmaking systems. Usually, the work time is just a matter of minutes. So, you will want to make sure you have your model and mold forms set up prior to mixing. To prepare the model and the forms, you can use a modeling clay or some other type of clay so the urethane or silicone doesn't run under the model or outside of the forms. They sell special devices that you can use as forms, or you can make the forms out of a container, wood, modeling clay, or legos.
Casting
Casting is the process of pouring a product into the mold to get a solid reproduction. There are many different types of casting materials. Your choice of product will depend largely on what type of chocolate or candy mold you will be making. If you are going to be making a vacuum form mold, you must make sure that your casting product can withstand heat. You can use plaster or hydrocal as an inexpensive option; however, these will break after a few uses because of the pressure of the vacuum sucking the plastic down on the object. Another consideration for vacuum forming is whether the item will hold heat. The best product to use is one that is aluminum filled and specially designed for vacuum forming, but they are quite expensive. Sometimes you can get away with using a less expensive casting material, and then filling it with aluminum powder or other aluminum fillers. Another option is to make the face of the item out of some of the more expensive material, and then fill the remaining part of the object with a less expensive product.
If you are going to be making silicone molds, your options for casting models are much wider. You can use plaster, wax, casting resins, and other rubber materials. Many mold making systems have counterpart casting resins. The casting resins can also be filled with other materials as well to reduce the weight and cost.