Wednesday, July 7, 2010

Mold Making, Day 3

Wednesday was spent putting the mother mold together.

In making a multi-part mother mold, each new piece is either defined by a clay wall, or built up against the (heavily lubricated) wall left by the previous piece. The image below has examples of both. In this case, the mother mold is composed of strips of burlap dipped a special plaster called FGR-95. FGR-95 is really meant to be used with fiberglass. I've built a lot of sculpture with FGR-95 and fiberglass (some of which can be found here), but that was in grad school, where the school supplied the fiberglass. Now that I'm paying, I'm using burlap.

Below is a bad photo of interesting moment. At this moment, I was midway through building the largest section, when I realized that the parting line I'd started wasn't going to release. The pieces of a mother mold aren't manufactured like a jigsaw puzzle, they're thick and imperfect. They don't slide neatly in and out. If they're too complicated, they don't go back together.

Sadly, I only realized I'd designed a locking system when I was putting in the second piece, so I had to improvise. Now I've got two little subsections in the middle. In the end, though, I'm not sure I could have done it another way. There's big undercuts there that could cause problems when it comes time to get the cast out. So I got lucky there.

Here's what it looked like, more or less, by the end of the day Wednesday.

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