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Max-Cast, Inc.
P.O. Box 662
Kalona, Iowa 52247

tel: 1-8_00-728-933_9
local: (319) 65_6-5365
M-F, 8:30am-5:00pm

Modeling Materials

Plaster is tough and inexpensive. It is not liable to crack, distort, or lose its shape, can be repaired, and is transportable. Be sure the model or platform is properly reinforced with wood, wire, steel, aluminum rods, and/or burlap. If the piece is big enough or complex enough to require disassembly to be molded, be sure it can be easily cut at those points. It is best to have your plaster piece completely finished rather than trying to do final finishing on each wax. It leaves the metal finishers no guide. This ultimately saves time in waxwork, particularly if there is to be a large edition. If a number of sand castings are required, the plaster pattern must be tough enough to stand up to the strain and be draftable. Rubber molds will often pull apart a plaster original although Dental Gel can be used on fragile pieces to obtain a limited number of waxes.
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Unfired clay is very difficult to use for either pattern making, rubber molding, or sand molding. It is liable to break, crack, and distort. Fired clay is much more stable and easy to work with. For sand molding, we prefer to make a rubber pattern of it first. Dental Gel can be used, if necessary, to mold a valuable fragile piece, but it adds expense.
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Plasticene is a much better medium for modeling because it does not crack, is easy to repair and can be used over other armature materials such as plaster or styrofoam. Transporting it can be a problem, particularly in warm weather.
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Self Hardening Clay
Self hardening clay has a lot of the same properties as plaster, but it is more expensive. It can be used thinly over styrofoam for larger pieces.
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Epoxy resin is useful for larger pieces since it can be formed with fiberglass, cloth or mat over Styrofoam, wood, and/or metal armature. Nice surface can be obtained. Detail is difficult. Some plastic patterns may react with rubber molding compound, and leave it sticky or discolored. It is always a good practice to do test samples. Reassembling resin models which have to be cut up to make a rubber or sand molds maybe difficult or impossible.
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Wood is an excellent pattern material. Historically, patterns for sandmolding have been wood. Carefully carved and drafted, these were used to make thousands of molds and castings. Wood can also be burned out of ceramic shell molds with an oxygen lance, but some ash which remains may be difficult to remove. Carved wood pieces can be used to make rubber molds quite nicely if wood is waxed, shellacked, or varnished.
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Most stone is okay, but porous stones and marbles should not be used since rubber and sand molds will stick and since binders in those compounds may discolor the originals. Again, Dental Gel can be used for a limited number of waxes from which a more permanent rubber mold can be made.
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Wax is an excellent medium for modeling and is very amenable to rubber molding. Although the original will probably be destroyed in the molding process, plenty more waxes can be produced from the mold. For larger pieces, wax maybe brushed hot over Styrofoam and modeled and carved to achieve the desired surface texture. An armature may be necessary to support a styro pattern and/or spindly waxes. It is good to remember to provide for the possible disassembly of the pattern to facilitate molding.
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Styrofoam can be used as a one-shot pattern invested in a sand mold (it is about the least expensive casting method going). However, the range of possibilities is somewhat limited with this method. As an armature material, styro is extremely useful since it can be covered with a variety of other materials: Epoxy resin, wax, plasticene, plaster and any number of other materials to provide the desired surface toughness and texture. Note that some things react adversely with styrene, notably urethanes and many solvents contained in other materials. It is best to try them on test pieces first.
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Bronze and Aluminum
Superficial damage may occur to the patina or paint on these pieces so repatination or painting may be necessary.
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If an external armature is used, be sure its horizontal stem from the main vertical member gives at least three to four inches separation from the piece. This gives molders room to operate and will help insure a sturdy mold. It is best if the support member falls on the mold's parting line on the side of the model or pattern.
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