Pate de Verre

For a brief history of pate de verre and kiln casting, click here.
Pate de verre, or paste of glass, the technique of pressing glass powders or frits, crushed glass the consistancy of sand, into a mold, is a detailed and difficult form of kiln casting. However, it is the use of these fine frits that give pate de verre its distinctive luster and allows for specific placement of colors in the mold.

Pate de verre utilizes the 'lost wax' casting method that other art objects are made of, from bronze sculpture to gold and silver jewelry.

Each piece starts with a wax model. The model can be an original carving or a duplicate made from a reproduction mold that is poured around the original carving or object.

A model is an exact replica of the finished piece and can take anywhere from a couple of hours to 15 or 20 or more to construct and/or carve depending on how big and complex it is.

I use wax for my models as opposed to other materials that molds can be made from because my work has undercuts which make it impossible to remove the model without damaging the mold.

I use a microcrystalline wax which is a dark brown that looks very much like chocolate and contruct my models by pouring the melted wax into shapes or sheets or small reproduction molds, combining elements, carving and smoothing and polishing using a variety of tools.

When the model is ready, it is glued down onto a surface so it won't float and a dam or cottle is constructed around it. This can be any water resistant material like plywood or sheet metal or clay but we generally use pieces of plate glass because we have a lot of that around here.

All the seams need to be sealed to prevent the investment, the plaster/silica mold material, from leaking out when it is poured around the model.

Pouring the investment. It takes about an hour for it to set up.

When the investment is set, the dam is removed. The wax model is now encased in the plaster/silica investment.

The wax model is then steamed out of the mold, hence the term 'lost wax'. At this point the model is gone forever and the mold is ready to be cleaned up and repaired if necessary.

The molds are now ready to fill with glass powders and frit.

The volume/weight of glass required to fill the mold is calculated and the colors are selected and weighed out into appropriate amounts. Frit crushed glass about the consistancy of powder or fine sand is mixed with a binding agent, we use a dilute solution of gum arabic, to form a sort of glass paste and the colored frit is placed selectively into the mold with small spoons, scoops, and spatulas.

After all the glass has been placed in the mold, it is set in the kiln and slowly brought up to casting temperature, 1400 - 1550 degrees, where it stays until the glass has melted and filled all the negative spaces in the mold. After the hold at casting temperature, it is reduced to the annealing temperature where it must rest awhile. Finally the kiln is slowly cooled over a period of many hours or days - the larger the piece, the longer it takes. If the kiln is heated too fast, the mold will crack and the molten glass will run out, if it is cooled down too rapidly, the piece will crack. When the kiln has returned to room temperatue, it can be removed from the kiln.

After firing the mold material, which now is soft like chalk, is carefully removed from the cast glass and the piece is washed.

The amount of cold work required varies with the piece and depends on how well it cast among other considerations. Excess glass is ground off using a flat lap. Finally, sharp points and rough spots are removed with diamond grinding bits and the surface is smoothed out with grit impregnated polishing points.