From: Widerman-AT-aol.com Date: Sat, 8 Mar 1997 02:22:25 -0500 (EST) Subject: Re: Types of Plaster The thickness of the mask skin in a plaster mold is determined not simply by how long it is left in the mold, but also by the thickness and moisture content of the plaster. Plaster soaks up moisture and, in theory, could be completely dried out, crushed and reused. A freshly made plaster mold contains a lot of moisture and will not draw out moisture from rubber or neoprene as quickly as a mold that has had more time to dry out. (Humidity will affect how quickly your mold dries out.) A thick plaster mold will draw out more moisture, faster than a thin mold. These additional variables are the reason why there is no direct length of time to skin thickness ratio. There are many variations and tricks you can employ in casting rubber such as the slosh method where you simply slosh rubber around the inside of the mold, adding layers of rubber until you have reached the desired thickness. Using a hair dryer can speed this process. This allows some control over varying the thickness in different parts of the mold.You can also dip felt in the rubber and use it to strengthen specific parts of the mask (usually the back of the head so it won't collapse from it's own weight, and the neck where the sleeve will attach. The face can remain thinner and pliable.) This will not work with neoprene. You can bake your mold at a very low temperature to remove moisture if you are in a hurry. Be careful not to overcook or the mold will crack. Allow to cool slowly. Hydrocal is much finer than wall plaster (also much more expensive). It takes detail better and is denser and stronger when hard. These may or may not be desired properties. I would recommend it if for casting small and highly detailed objects. I prefer plastecine to pottery clay. -Steven-> --- Personal replies to: Widerman-AT-aol.com --- List replies to: puptcrit-AT-lists.village.virginia.edu --- Admin commands to: majordomo-AT-lists.village.virginia.edu
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