Monday, July 5, 2010

Mold-making, Day 1

An incredibly tiring, but (apparently) successful day.

It was supposed to get to 100 today, and I wasn't sure my window AC unit would keep the studio cool enough to prevent the mold rubber from being effected, so I got an early start.

First step was to build a clay wall to catch the rubber as it runs off the mold.

If the figure looks shiny, it's because the second step was to coat everything with vaseline (thinned with mineral spirits). I used about a 50/50 mix to paint the base, and a 90/10 mix in a spray bottle for the figure itself.

After that, I whipped up a quick foam-core mold that I filled with the mold making material, which eventually set into long strips of hardened mold rubber, about 1/2 x 3/4 x 20 inches long. Later, I pinned these to the sticky surface of the mold to ensure proper registration between the rubber and the mother mold. This was Justin's idea, and it looks to have worked out great. Thank you Justin

After that, there was nothing to do but pour the rubber. I'm using Polytek 74-29 (also on the advice of Justin and Darla), and one of the cool things about it is that it's black. Looks like a Gulf Coast vacation.

The first pours were easy. The 74-29 is a little more viscous then some of the other materials, but it moves easily, and fills nicely. It didn't take any time to get the whole figure covered and looking like this.

From there, things slowed down considerably. The problem with brush-on molds (as opposed to poured box or blanket molds) is that that you spend a lot of time moving the material around, waiting for it to set up. You can thicken the material with cab-o-sil or polyfiber II, which I did, but getting it where you want it is still slow, tricky work. A little like trying to ice a cake with motor oil.

The other problem is that it's hard to know when you're done. In theory, the goal is to get an even 3/8ths - 1/2 inch layer over the entire piece. In practice, after you get everything covered, and touch up the obvious light spots, it's hard to figure out depths. The hard part is that if there are thin spots in the rubber, you won't know it until the end, when it's too late. Better to err on the side of caution, add another layer, and hope for the best.

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