Tuesday, August 17, 2010

mold work on the Terre Haute commission

This is my 100th blog posting! The clay work for the Terre Haute family group was approved. The next step is to make molds of the sculpture and send them to the foundry, to become bronze.

The sculpture must be cut into pieces, to make it manageable for making molds and pieces that the foundry can pour at one time. We removed the heads first, using a wire tool.

Next, we used a sawzall to cut off the arms, which were then mounted upright onto waiting boards with pins. It is intensely nerve racking to cut up a sculpture that I've worked on for months.

Then, the children were cut up and removed, leaving the two adult torsos and legs. When everything was cut into handleable sizes, there were 17 separate pieces to be molded.

The mold work was turned over to Don and our neighbor, Steve McMillen. Steve helped Don on the Home of the Innocents sculpture groups last year. Steve is mixing the 2 part rubber Polygel 40 that we buy from Polytek. Even though we bought the mold compound in 5 gallon buckets, they pour the compound into separate quart cans, to keep down spillage. Notice the plastic sheet - mold making is messy, no matter how careful you are.

The first coat is the most important, as that picks up the surface details. You have to make sure that the rubber compound is pushed into every crevice, and that there are no bubbles.

After the first coat becomes hard, but still tacky, they apply a second coat. When it has gone off, but still tacky, thet apply the part-line shims. They use bubble sheet from sculpture depot in Loveland, Colorado. The sheet is cut into long strips, and those strips get smeared with trewax. Don is cutting the bubble sheet to follow the contour of the sculpture. He makes cuts where the curves are too sharp for the strips and tapes the pieces together with a special tape that we get from sculpture depot. The strips are attached to the sculpture temporarily with straight pins, right through the rubber coat and into the clay.

"...there's no place like home..."

They mix up a regular batch of rubber (equal volumes of part A and part B), and then mix in this light fluffy stuff called Polyfil 2 that we get from Polytek. It makes the rubber compoung stiff, like cake icing. They put it into a plastic baggy, cut the corner and apply it along the seams. Don uses a knife to smooth it out. They have seen people use a short cut by squirting a bead along the drawn-on part line and stick in plastic shims, without the fuss of cutting, taping and pins. It's a little sloppy, so they prefer to take the extra steps.

A third, fourth and fifth coat is applied over the shims and sculpture pieces. Then, they mix up more rubber with polyfil (to a thick icing consistency) and apply it with a plastic knife to areas that have any undercuts. A plaster mother mold will be applied to each mold. Those mother mold pieces have to come off easily, so there can't be undercuts that will hold the plaster.

A final sixth coat is applied, as sometimes the surface of the polyfil mix can be rough. The manufacturer recommends that you only start what you can finish that day. Don and Steve have finished 11 out of 17 pieces at this point. When they finish the rubber work, they will apply the plaster mother molds.

1 comment:

Anonymous said...

Congrats on your 100th post! Nice to see the in process shots of how you make your molds.