Saturday, August 1, 2015

09 Plaster Production Molds Nº 257

Because I ran short of clay on this build-up, I was not able to cover the underside. So what I did was roll out some very thin coils of clay and put them all around the edges of the build-up where it meets the coddles. Click on any image to enlarge it.

Then I used a 1/4 inch wooden dowel to press the coil all around the inside edge of the coddles in order to seal it. I used the dowel because my fingers are slightly too big, and my fingernails have a tendency to jab the build-up. I think it is now ready to pour some plaster. I always wait until I have an uninterrupted block of time to pour plaster. That takes away some of the stress of plaster mold making.

Some arithmetic:
The inside of the coddles measures 3.5 x 8.25 x 9.125 inches.
That makes a total volume of 263.48 cubic inches.
2/3rds of that will be the amount of water, so 263.48 divided by .67 is 175.65 cubic inches.
There are about 14.44 cubic inches in one cup of water.
175.65 divided by 14.44 is 12.16 cups of water.
I am going to subtract two cups of water for the carving wax upper torso that is sticking up in this part of the mold, so that leaves about 10 cups of water for this mold part.
The ratio of water to plaster is 2:3, by weight.
Water weighs about 8 ounces per cup, so 8 x 10.16 is 81.28 ounces of water.
That means that one part of water is 40.64 ounces.
There are three parts of plaster, so 3 x 40.64 is 121.92 ounces of plaster.
81.28 divided by 121.92 is 0.66666_. That is the 67 consistency that I want.
There are 16 ounces to a pound.
81.28 divided by 16 is 5.08 pounds.
121.92 divided by 16 is 7.62 pounds.
So what I want to do is weight out 5.0 pounds of water to 7.5 pounds of plaster.

Links To BJD Tutorials Updated 1 August 2015

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