Casting Polyester Resin
Polymers generally shrink when they cure. If polyester resin is cast in a form, this shrinkage can cause total failure if the piece has a complicated shape. The hardening process generates heat, which dissipates very slowly in the resin. Therefore, thick areas harden faster (and shrink more quickly) than thin ones. The result is a crack in the thinnest part, which stayed liquid longer and had to relieve the stress. For this simple reason, most polyester sculptures have boring shapes: pyramids, cubes, and so on. It is obvious then that the very complex shapes of the pieces by Eda Easton required a very special casting process.
To begin with, the pieces were sculpted in clay. A plaster mold was then made, from which a plaster original was cast. The sculpture in plaster was then surrounded by a silicon rubber mold, which was embedded in a plaster mother mold and carefully sealed at all seams. The liquid resin, containing the polymerization catalyst, was poured into this form.
Because of the toxicity of the vapors of the liquid resin, which is a solution of the pre-polymer in styrene, Eda and her coworkers wore protective gear, thick rubber gloves, and a face mask with a carbon filter to absorb the vapors. When the casting was done, the studio was abandoned for two days.
How did they avoid the shrinkage problems and how did the chrome-plated steel get into the sculptures?
The first problem was handled after consulting with various researchers in the polymer field. Adding only a very small amount
of catalyst extended the so-called gel phase, in which the polymer is just barely solidified. This had two benefits: even the bulky parts of the sculpture solidified more slowly and the entire sculpture had plenty of time to relax and cure all internal tensions. The polymerization process was made to last seven to ten days. After the initial settling of the liquid polymer into all crevices of the mold had stopped, the steel parts were gradually lowered to where they belonged; external guide marks had been carefully established to make this a precise operation.
Once the pieces were taken out of the mold, they were allowed to cure completely for several weeks before the surface finishing could begin. This was arduous work, first with coarse tools, then with finer and finer sandpaper, and finally with fine grit polish. Because power tools were found to do more damage than good, this process took weeks and much manual labor.
Having the clear resin without any fillers or other additives gives these pieces their unique transparency with many internal reflections. The most interesting part of the entire creative process is the way in which the artist had to anticipate the effect of these reflections in the resin sculpture while working on the original in clay! One can get a feeling of this and have an interesting comparison by looking at the bronze casts of two of these pieces: Leda and the Swan and Folie a Deux exist in both media.
