Why would you want to do a full-body lifecast? I can think of only two reasons that apply to makeup effects work for stage or screen. The first is for the purpose of creating a body or corpse, in which case the task is somewhat easier because the lifecast will most likely be done with the subject in a prone position. The second would be for the purpose of creating a body form that will be used to create a sculpted costume or body suit.
To do a full body, front and back, will require about 15 lbs. of alginate (about $120, or £61.5); to do the same job with a skin-safe silicone will require about 3 gallons of (platinum) silicone. The cost difference between alginate and silicone for a project of this size is enormous. You must know before starting what your time allotment will be to perform the task and whether or not you will need more than one "pull," or copy, from the mold. The advantage to using silicone is that you do not have to make a stone or foam positive from the mold
immediately because once silicone has set, it will not dry out and any shrinkage will negligible. With alginate, a positive must be made fairly soon after the alginate mold is removed because it will begin to dry out quickly due to the water it is made with. However, if you need to make multiple copies, you can make a silicone mold from your positive using a much less expensive tin silicone.
Before we go any further, let’s also discuss the materials we could use for casting our positives: oil or wax clay, Ultracal 30, plaster, Hydrocal, or urethane. Here are the characteristics of each:
■ Sulfur-free oil-based clay or wax-based clay is ideal for melting and brushing into molds where additional takeaway sculpture and texturing may be needed. Often, rigid urethane foam is cast as a reinforcing element to the positive after the clay has been brushed in and allowed to cool. Rigid urethane foam is lightweight and can be quite strong.
■ Ultracal 30 has the lowest expansion of any rapid-setting gypsum cement available. Ultracal was designed to give the patternmaking industry the ultimate in a gypsum cement tooling medium. It is also ideal in the makeup effects industry for its ability to withstand repeated heating and cooling, which is necessary when fabricating foam latex appliances. Since prosthetic appliances must fit precisely to sell the illusion of reality and believability, Ultracal is outstanding mold making due to its exceptional hardness and accuracy of detail.
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Impression dental plaster and Lab dental plaster are harder than regular Plaster of Paris; they set faster and have a negligible amount of expansion compared to Plaster of Paris. However, I would not recommend any plaster as a casting medium for prosthetic appliances; in fact, I would not use plaster of any kind for prosthetic fabrication except as a mother mold/shell material or as a core model that will be reworked and molded again.
■ Hydrocal® from U. S. Gypsum offers higher strengths than typical plaster products (such as #1 Potter’s Plaster, Impression dental plaster), though it is not as strong as Ultracal. It can be used in a variety of arts and crafts applications in addition to makeup effects work. Hydrocal is especially designed for thin sections, which require high green (early) strength to minimize breakage during removal from intricate molds.