Saturday, December 22, 2012
08 Joint Design Nº 45
I mixed and poured the first half of the plaster mold. I used the mold table vibrator when pouring the plaster. I always let the plaster set up for at least an hour without fussing with it. Click on any image to enlarge it.
To make the plaster mold making less stressful, always have a lined trash can and a bucket of water ready. Excess plaster can be scraped out of the mixing bowl, into the trash can. The mixing bowl, stirring tool, and hands can be washed off in the bucket of water. Never put plaster (dry, wet, or set) in the drain pipes.
Once the plaster has set up, the coddles can be removed. The oil-clay I used to seal around the bottom of the coddles can be seen on the molding table.
This is the mold flipped over, showing the other side of the pattern. I remove the ring of oil clay that was supporting the pattern, as well as the pads of clay that were supporting the matter board build-up. I also clean off any plaster that leaked through the build-up.
The matte board build-up is being removed from the pattern and mold.
The first half of the plaster mold with the pattern embedded in it.
I carve four registration keys into the first half of the plaster mold.
I apply a parting agent to the pattern and the plaster. Plaster sticks to plaster, so a parting agent is needed, otherwise the two halves of the mold will stick together, locking the pattern inside the mold. I use a 50/50 solution of liquid soap/water as a parting agent. I apply the parting agent to the mold until the mold no longer absorbs the solution. Then I mop out any excess parting agent with my brush.
I put the coddles around the plaster and reseal the oil-clay around the bottom of the coddles by pressing the clay coils down with my fingers.
I measured out 1.5 pounds of plaster first. Then I put my mixing bowl on the scales and measured out 1.0 pounds of water. The ratio I am using is 2 parts of water to 3 parts of plaster by weight. The part that I am using is 0.5 pounds. Then I rapidly sift the plaster into the water as evenly as I can, until all the plaster is in the water. I let the plaster slack until all of it has absorbed water. Then I push the plaster under the water and stir it. I stir it until it is smooth and creamy.
I turn on the mold table vibrator and pour the plaster evenly over the pattern in the coddles until it is completely covered by about an inch or so of plaster. I let the plaster set up for at least an hour.
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