Beginning a mold

moldHere’s a photo of a new sculpture, in the first stage of moldmaking. I spent the weekend at Open Studios trying (and occasionally failing) to describe this basic moldmaking process, but here it goes again.

I’m making a reusable “glove” mold on this lifesize half figure. The figure was sculpted in a red earthenware clay (the color you can see through the greenish mold rubber), which I let dry to a leather-hard stage which stands up better to the rigors of the moldmaking process. Over the clay I spread several thin layers of Polytek’s Polygel 40 mold rubber. This mixes 1:1 by volume, a fairly forgiving mix for a plastic but this is thankfully typical of Polytek’s products. Since this is the first time I had used a gel rubber (actually polyurethane), I found that it hardened up a bit suddenly and I got stuck with several drips and a few untintentional gaps. Next time I will mix it with some poly-fiber (although the company says this is not necessary) to make a more evenly-spreadable resin in the liquid stage.

I then fastened a strip of cast rubber about 1″ x 1″ x 36″ around the top of the figure (cementing it on with more liquid rubber), which will ultimately form a dividing line for the two pieces of the hard backup shell. I added a wall of plastelina on top of this, making a fairly solid dividing line for the backup halves, which I will make in hydrocal.

After I make the hydrocal outer shell, I’ll remove it as soon as it sets up completely, then cut the seam line (that cast 1×1″ strip you can see running around the top of the head and shoulders) of the rubber mold until I can peel it off easily from the clay. Usually the clay original is pretty badly destroyed in this stage, but occasionally I can retrieve part for another use. Once I put the rubber halves, and then the covering shell, all back together again, I can fill the rubber mold with a number of materials: plaster, wax, cement, or polyurethane hard plastic.


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