| Many of my pieces are cast using a sand
mold process that is very similar to traditional metal foundry
practices. This green sand is actually a
crushed volcanic rock (olivine), that is mixed with a specific
percentage of dry clay (bentonite). The bentonite gives this mixture some
stickiness so that the pattern can be pressed with greater detail.
The green sand is moistened and screened into a metal casting box. Then I press my original pattern (made of wood, plaster or wax) into the sand, making sure that it is perfectly level. Any low spot would lead to an over pour with the glass spilling over the lip of the mold.
After removing the pattern I screen
powdered glass into the mold. I use stencils and free hand drawings to
add images to the surface. In this process there is no room for errors
since nothing can be erased without disturbing the delicate mold.
I usually prepare the drawings that float inside the casting (inclusions) the night before. They are meticulously laid out on a steel surface using crushed and powdered colored glass. Great care must be taken to ensure that the finished drawing will fit within the confines of the final casting. Since the images are frequently layered one on top of the other the final composition must also be carefully considered from the very beginning (example).
| At this point I am finally ready to bring
in my team of assistants for the actual casting. Depending on the size
of the piece, I work with a team of three to ten or even twelve people.
First I pour a little glass onto the drawings on the steel. After a few
moments when these have sufficiently cooled, I begin pouring glass into
the larger mold. The smaller castings with the images are then laid into
the larger casting between ladles of molten glass. Since both the
smaller and the larger castings are of
the same glass, and everything happens hot and fast, they melt together
with hardly a trace of separation (example).
| There is again no room for errors and no
way to fix mistakes. After literally hours of preparation the
interaction with the molten glass takes only a few extremely exciting
minutes. The team has to work like a finely tuned machine. For a large
piece involving up to a dozen people we will frequently do a "dry
run" to choreograph everybody’s movements and actions. This is a
"team sport" that is not without personal risk. We pour the
glass at close to 2300 degrees Fahrenheit, using steel ladles that weigh up to 25
ponds when empty. After
the pour, while the casting is "setting up" we keep the top
surface "warm" using propane torches with three to four foot
long flames. After torching the casting for several minutes we move it to the annealing oven. Here the casting is
cooled at a computer controlled rate from 930 degrees Fahrenheit to room temperature over
a period of two to ten days depending on the thickness and mass of the
© Copyright 1999 by Vitroglyph, Inc.™ and Henner Schröder