On Slipcast Glass

 copyright 1992 Louis Katz

all rights reserved

Although not clean, clear and glossy like glass, cast glaze is a far cry from the earthen incinerations that lie close to my heart. The process was a product of circumstances at Illinois State University where I spent my first year of graduate school. Joel Meyers, who runs the glass program, had managed to have a truckload of refractories donated to the school. The glass department, housed in a building too small for the program, was filled to the brim with ceramic-fiber products. Equipment was buried behind boxes of fiber, and the question soon arose as to whether the fiber was worth its storage space. An excess of expensive material underfoot is a great instigator of experimentation. Not only might I never have gotten a chance to use stuff like this for free again, its use was a space-saving public service. Consequently, glass was blown into ceramic-fiber tubes; molten glass was poured into other forms; fiber was wrapped, compressed, ground, melted and then disposed of.

Before the fiber's arrival, I had already been trying to visualize a way to cast glass with thin walls. Thick glass can take weeks to anneal properly, and beginning glass students were discouraged from making anything thicker than 1/4 inch. The traditional glass-molding material is a mixture of plaster, sand and silica flour. It is inflexible and requires that complex glass forms be cast with thick walls. But ceramic fiber is flexible. Forms cast in it can be thin. The fiber's flexibility relieves any stress from contraction that the mold might put on cooling glass. My first piece was made with cullet I had ground to a fine powder in a ball mill and mixed with water. I poured it into a small bowl made from ceramic-fiber paper, then poured it out. This left a thin glaze of cullet on the inside of the paper. When it was dry, I put this mold into the kiln and fired it. Afterward, I peeled the fiber paper off and was left with a bowl of very thin glass. I was fortunate in that this piece came out of the kiln intact, as I was soon plagued with a breakage rate exceeding 70%. Casting glaze is fraught with difficulty. Cracks that form in the glaze coat of clay vessels generally don't destroy the structural integrity of the body. Not so with glaze only. A crack is a crack, and cracks were hard to avoid. I never knew what caused them. If the kiln fired too slowly or too quickly, it cracked. If a piece of sand or anything else fell into the glaze, it cracked. If you were mean to your little brother in a previous life, it cracked. Theorizing that fiber in the glaze was causing cracks by not shrinking at the same rate, I tried using lower-expansion glaze recipes, elaborate cooling cycles and burning incense. Eventually, I did surpass the 50% survival rate. I figured that if I could sell the pieces for enough money, the losses wouldn't matter. I was lucky it worked at all. Besides, a 50% success rate doesn't drive one nearly as crazy as a 70% loss rate does.

New problems continued to crop up, though. When I was invited to be a visiting artist at the New York Experimental Glass Workshop in Little Italy on the isle of Manhattan, I ground 50 pounds of glass, set the slurry in the back of my car and drove from Montana to New York. On arrival, I discovered that the ground glass had settled into a rock--not the normal too-much-feldspar in-the-recipe kind of rock, but a solid, capable-of-deflecting substantial-swings-of-a-hammer concrete. Not to be outdone by what was once a slurry, I went to Canal Street and bought a blender. After crushing the rock with a hammer as best I could, I threw it in. Within a few minutes, I had a few quarts of glass slurry and stubs instead of blender blades.

Since then, my feelings about such casting--including the work I made and whether or not I will ever make more--have vacillated. gave up using the technique in 1988 after reading health warnings that came with a new roll of fiber. It was a good excuse. I had been coming home itchy, going to bed itchy and waking up itchy. Those who worked near me were also glad to be rid of the stuff. The rubber cement I used to hold the molds together would burn off in thick clouds of odiferous black smoke that would offend the unsuspecting nose at a quarter mile. The binder continued to stink even after the cement had burned off. Part of my feelings toward the process must also be a result of comments by others concerning cast glaze's "lack of conceptuality," its "craftlike presence" and "inescapable relationship to the process." Their incessant cries for "content, content, content" seemed to imply that all I was making were empty vessels. Was I duped by that bag of bull? Did they provide just enough pressure to turn me away from a Fiberfrax destiny? After all, I had sold a few pieces right away. I made some more; I sold some more. One piece was broken in a gallery after winning a cash award. The postal service ate and paid for another. Cast glaze was a commercial success.

I started my last cast-glaze pieces in 1988. A trip to Thailand interrupted the cleaning process, and they were packed away, already fired but still in their fiber molds. Since then, concern over my exposure to bits of devitrified ceramic fiber while peeling the fired pieces has kept me from making more. In 1993, I peeled the molds from the pieces cast in 1988. I still worry about the hazards of fiber. The warnings mentioned a 1500degF threshold for devitrification to occur, but perhaps I could fire lower than that. As I look at my small collection of this work, I wonder if I can still put myself in a space where I can use pinks and light blues and make more pretty things. I wonder how far back I will need to go to bring cast glaze forward, and when and where I should leave it.


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copyright 1997 Louis Katz