File spoon-archives/puptcrit.archive/puptcrit_1997/97-03-11.140, message 213


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->


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