Friday, September 7, 2012

05 Molding Design Nº 8

I have already mentioned Tim Bruckner's book, Pop Sculpture, in post 05 Molding Design Nº 2, as a reference for making silicone rubber waste molds.

Tim Bruckner models an original oil-clay figure over a wire armature, then cuts it apart in order to make molds of the parts. His choice of a waste mold material is silicone rubber. Tim uses a combination of old, chopped-up silicone rubber molds and new silicone rubber to make a one piece block mold over the original oil-clay part. He makes a tube of a three- or four-ply paper called Kromekote, generally used for pen and ink illustration, which he tapes together with masking tape. Then he places the mold in a pressure pot, which he pressurizes to force the new silicone rubber into the spaces between the chopped-up pieces of old silicone rubber.

Once the silicone rubber has set, he removes the block mold from the pressure pot and cuts it open in a zig-zag pattern on one side to release the original oil-clay model. Silicone rubber is flexible, so only one cut is needed to release the oil-clay. After cleaning the inside of the mold, he bands it, and pours his wax into the mold to make a carving wax part.

Wax does not stick to silicone rubber. The wax thickens along the walls of the mold, just as it does in a water-saturated plaster mold, or a moist moulage mold. Since the mold is a block mold, which is cut open, no mold separator is needed. The single zig-zag cut on one side means no registration keys are needed. Furthermore, silicone rubber has a long shelf-life (similar to plaster). Chopping up old silicone rubber molds to use in waste molds means that it can be reused as well.

It sounds like silicone rubber is an excellent choice for making waste molds. However, there are a few technicalities that would keep me from using this method:
1. Silicone rubber is very expensive compared to plaster or moulage.
2. You need to have some old molds to chop-up, in order to make waste molds.
3. An air compressor and a pressure pot are needed to make the waste molds.
4. A certain amount of new silicone rubber is needed for each new waste mold.

Other than that, if a doll maker already has some old silicone rubber molds, an air compressor, and a presuure pot, then this might be a good way to do it.

Plaster is the oldest mold making material, dating back to antiquity. Moulage has been around for over one hundred years now. Silicone rubber is the newest mold material for making waste molds. Each material has its advantages and disadvantages.

The purpose for making a waste mold is to translate the oil-clay into carving wax. This is done because the oil-clay, while easy to model into a figure, is too soft to be test-strung when designing ball and socket joints, and cannot be refined to a high surface finish for making the final molds. Carving wax is tough enough to be test-strung, and can be refined to a high surface finish for making the final molds.

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  1. thank-you Kirsten: please add many more pictures of the step by step process. It is clearing things up for me emensly!1!! Im really gratefull you are doing this blog it will help so many of us just tring to make something we can be proud of and to call our own.

  2. You're welcome. I am happy to know that my daily doll making journal is of some help to others.


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