Tuesday, October 30, 2012
06 Waste Molds Nº 50
Plaster Waste Molds
This is an old picture of plaster molds soaking in water in order to become saturated with water for casting wax into. The working principle is that water and wax do not mix. If molten wax is poured into dry plaster molds, then the porosity of the dry plaster will absorb wax into the walls of the mold, and the mold and the casting will be ruined. Remember to soak plaster rough shell molds in water until they are thoroughly saturated with water before casting carving wax into them. Click on any image to enlarge it.
Plaster rough shell molds are made using the dry lake bed technique of mixing plaster. In this technique, an estimated amount of water that equals the volume of plaster to be poured is put in the mixing bowl, then plaster is sifted through the fingers evenly into the mixing bowl until a cracked dry lake bed pattern appears. Plaster is always added to water. Once the plaster has slacked for a minute or three, push the dry lake bed under and mix with hands and fingers, squeezing out lumps until the plaster has a creamy consistency. Then pour the plaster into the mold box, covering the model. Martha Armstrong-Hand used water saturated plaster rough shell molds to translate her oil-clay doll figure into carving wax doll parts.
One of the reasons we make molds is to create a record of the work. Plaster rough shell molds may be used to create one or more carving wax patterns or models. Because the carving wax thickens around the walls of the water saturated mold, hollow castings may be produced. One thing about plaster rough shell molds is that the plaster may not be reused to create a new mold. Also, because the dry lake bed technique does not produce a very strong mold, these waste molds do not last very long, if more than one carving wax casting is wanted. These plaster rough shell molds are now taking up space in my studio. I have never used them to make any new carving wax castings. This is one reason why I decided to use hot-melt moulage to make my waste molds for casting carving wax. The hot-melt moulage may be reused many times for making new molds.
Silicone Rubber Waste Molds
While silicone rubber may be used to make waste molds of an oil-clay doll figure for casting carving wax doll parts, it is much too expensive for me to use at this time. It requires an air-compressor, a pressure pot, and old, chopped-up, silicone rubber molds. Also, a certain amount of fresh silicone rubber is used to bind the chopped-up molds, so it is much more expensive than either plaster or hot-melt moulage. However, it is nice to know that the old silicone rubber molds can be reused in such a way. One other thing to mention is that a silicone rubber mold does not rely on water in order to resist sticking to carving wax; one of the properties of silicone rubber is that it resists carving wax. More information about this technique can be found in Pop Sculpture, by Tim Bruckner, et al.
Hot-Melt Moulage Waste Molds
With this third version of my doll, I did not make any plaster rough shell molds for casting carving wax doll parts from oil-clay doll parts. Instead, I used hot-melt moulage, a molding material in the alginate family. Hot-melt moulage is reusable. It is melted in a non-aluminum double boiler, then poured into the mold box. Once it cools, it sets up into a semi-flexible mold which may be cut with a mold knife, if made in one piece, or also made into multiple piece molds. Because the moulage has a lot of water in it, and because water and wax do not mix, it is a fabulous substitute for plaster rough shell molds. It must be kept moist in order to reuse it. After the casting is made, the moulage waste mold is chopped up and stored in containers with tight fitting lids so it will not dry out. I use Atlas Mason jars to store my moulage in, in between uses. Each jar holds about one pound of moulage.
Here is the reusable hot-melt moulage, stored on a shelf in the studio until its next use. Hot-melt moulage is usually used to make molds for casting plaster or wax models.
This is the last post for making moulage waste molds over the oil-clay doll figure, which were used to translate the oil-clay doll parts into carving wax doll parts for further development. Next I will discuss making carving wax in the studio, carving wax tools, and some techniques of working with carving wax. After that, things will start to get exciting, as joints are designed, and the carving wax doll is designed, then refined for use as patterns or models for the final slip casting molds.
I try to do a little bit of work on my doll every day. I am figuring it out as I go along. I am trying to follow the method of making a slip cast BJD as outlined by Martha Armstrong-Hand, in her 1999 book, Learning To Be A Doll Artist: an apprenticeship with Martha Armstrong-Hand. It is an awesome method of making a multi-media figurative sculpture that is fully articulated, with ball and socket joints, tensioned with springs or elastic.
A dead-tree version of LTBADA is currently out-of-print and unavailable. If you do not have a copy of this book, please check the Martha's Method topic at Woodland Earth Studio for a reconstructed version of the book, based on the Table of Contents of LTBADA.
According to the TOC of Martha's Method at WES, I have just finished 06 Mold making. The next step is 07 Carving Wax.
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