Moldmaking Step by Step
Molds can be made from many materials. You can choose plaster, clay, natural rubber, or silicone rubber. Whichever material you use, the basic technique is the same. Follow these steps carefully to insure success.
Carefully choose the shape you wish to duplicate. Obviously, simple shapes are easier than complex shapes. Take some time to examine the piece and determine if it is truly suitable to use as a model. That wonderfully interesting widget with all sorts of protrusions might look great as a knick-knack — but how hard will it be to get wax out of a mold made from it? If the model you want to duplicate has “undercuts,” a one-piece mold is not advisable. Determine which direction the mold will come off of the model. Will it have to be pulled off in such a way as to risk damaging the hardened wax inside? Ask yourself if the model lends itself to being made as a one-piece mold. If not, you'll have to devise a two-piece mold.
Problems: Draft and UndercutThe biggest problems for the moldmaker are draft and undercut. Draft is the taper form intentionally given to molds in order to make removal of the candle easier. An undercut is any flaw — such as an indentation or protrusion — in the model. Undercuts make candle removal (from a one-piece mold) difficult, if not impossible.
The shape you choose from which to model your mold is the clue to easy or hard removal. Latex molds can be peeled off like an adhesive bandage. However, remember that hardened wax is frangible. Trying to peel off a mold from the outstretched wings of an angel might break them off. So when choosing models, take their basic shape into consideration: the simpler the better (and easier).
If you want to make really fancy shapes, there are many good books available on candle moldmaking. Your craft store may carry a line of candlemaking books. Or, search the Internet's many candle Web sites. Your library is also a good source.
There is no one best material to use for making your own molds. As you experiment and gain experience, you may well develop preferences. You may find one or another material easier or more difficult to work with. Once again, there's always a lot of trial-and-error to home candlemaking. That said, here are some general guidelines for moldmaking substances.
Clay — Clay is an excellent substance for replicating a shape (model) you have made yourself. It's hard to reuse and best for making one-of-a-kind shapes. Don't attempt to use clay for quantity candlemaking.
Latex — Latex is fairly easy to use as a brush-on liquid. (See “Making a Latex Mold: A Step by Step Guide.”) However, latex is somewhat time-intensive as you have to apply ten to twenty coats and wait for each one to dry before applying the next. The good news is that a latex mold can be reused several times, sometimes — depending on the shape — as many as twenty. The downside of latex molds is that they shrink as they dry. This can distort the shape. To avoid this problem, simply support the mold as it is drying. Although latex can be reused, it's also great for a single use, especially if you are using an odd-shaped model. Be prepared, however, for your candle to emerge from the latex mold a bit smaller than the mold itself.
Natural Rubber — Natural rubber has many advantages. It is flexible and easy to handle. However, it has one big disadvantage: you can't use stearin with a rubber mold. A chemical reaction between the two will ruin the rubber due to the corrosive quality of stearin (stearic acid). The good news is that natural rubber can be reused with candles made from wax that doesn't need stearin as an additive. If you want to use a natural rubber mold just a few times, you can use stearin as part of your wax mixture because the chemical corrosion is a slow process. But, eventually, the stearin will make pits in natural rubber.
Plaster — Plaster of Paris makes excellent molds but it is entirely without flexibility. From a practical standpoint, plaster is best used to make a master mold from which you can then make molds of flexible material. Plaster can be used to create a two-part mold.
Polysulfide — This material is reasonably priced and fairly easy to use because of its flexibility. It can be poured over almost any object. Just remember to coat the model with a releasing agent. Petroleum jelly and liquid soap are good.
Polyurethane — This substance is inexpensive and mixes up easily. It is not advised for quantity production, especially if you are using stearin as an additive. Like natural rubber, there is a chemical reaction between the two, though less severe. The downside to polyurethane is that is doesn't keep well. You have to plan to use it as soon as you open the can. It's probably best used for molds with which you are going to do a short-run production of no more than a dozen candles, and make them at the same session of candlemaking.
Every mold material (except plaster bandages!) comes with a sheet of instructions and information about the material's attributes and recommended uses. Be sure to read it and follow all instructions carefully. You may need to wear rubber gloves or take other precautions.
If so advised, be sure there is sufficient ventilation when using the moldmaking material. This caution cannot be emphasized enough, especially when using the chemically based materials.
