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VARIOUS TYPES OF KILN CASTING Scroll down to view & read about various types of kiln casting, and to see why this type of glass can be so expensive! Hollow Core Vessels Ancestral Journeys ©Jamie McKay 2005 Gaffers Lead Crystal Mysteries & Memories ©Jamie McKay 2005 Gaffers Lead Crystal Life Came Pouring Out ©Jamie McKay 2004 Gaffers Lead Crystal Ancient Waters ©Jamie McKay 2003 Gaffers Lead Crystal Dreaming the World into Being ©Jamie McKay 2003 Gaffers Lead Crystal Solid Sculpture  The Great Void ©Jamie McKay 2002 Gaffers Lead Crystal | Open Face Casting ~ Bas Relief Tiles The luminous finish on these tiles is created by firing glass frit in an open face mold made of plaster & silica. The side of the tile in contact with the mold's surface obtains a soft matt finish, while the side exposed to the high heat of the kiln obtains a fire polished surface. (More info below describing various kiln casting processes.) 
Neo-Lav Lady ©Jamie McKay 2007 Bullseye Soda-Lime Glass  World Tree ©Jamie McKay 2007 Recycled Bottle Glass 
Test Tiles ©Jamie McKay 2007 Recycled Bottle Glass  By the Light of the Moon ©Jamie McKay 2001 Gaffers Lead Crystal | Variations on Kiln Casting (click on pate de verre above to see & read about this specialty form of kiln casting) Quick Overview: There are as many ways to create a model as there are ways and recipes to create a refractory mold, both of which you need when making a piece of glass art using the various kiln casting techniques shown above. Casting models are typically made from clay or wax and then invested with fireable mold material (refratory molds). The model is removed (directly or by some lost wax casting technique), the empty mold cleaned, and then fired in a kiln in such a way that a specific amount of glass will melt into the mold's empty spaces. Everything is brought down to room temp after having been fired according to a precise schedule that controls the heating, annealing, and cooling phases. The mold is then devested so that the glass piece that was buried inside can be removed and then coldworked to reveal a gorgeous piece of luminous glass art ~ assuming everything went according to plan! More Detail: Bas relief tiles tend to be made from clay; the tile is then invested in a mold called an open face casting by pouring a slurry of plaster silica into some type of mold containment form (such as a coddle box, tin pan, tar paper form, etc). If the model material would not be easy to remove from the mold's interior (such as with a hollow core vessel or with a solid sculpture containing major undercuts that would trap the model inside the mold), the model is usually made of wax with sprue channels and vents added to the final wax form to help ensure that all areas inside the mold will be filled with glass during the firing process without trapping air bubbles. The sprued wax model is then invested in mold material by either pouring into the containment form OR by handbuilding the mold to build up multiple layers around the model. There are many different recipes for making refractory molds (molds that have to endure high firing temps), but they usually revolve around equal portions of plaster and silica ammended with other refractory or strengthening materials such as sand, vermiculite, grogs, fiberglass shorts, ceramic shell materials, etc). Face coats are sometimes applied to the model before the actual mold material is applied or poured, and these pre-coats can include talc or kaolin (epk) in a plaster silica base, to help the mold material come away from the glass surface more easily after the firing is completed. Once the mold is created and cured, the model is removed either directly (as in clay from a tile mold) or by steaming/melting out the wax in a hollow core mold via a process called Cierre Perdue or Lost Wax casting. The now empty mold is rinsed and then loaded & leveled in the kiln. The appropriate amount of glass (frit, cullet, billet, or sheet) can either be piled directly into the mold (as with an open face casting for a tile) OR suspended in a crucible (w/ a hole in the bottom) over the top of the mold so that the glass will melt & pour into the mold during the high temp portion of the firing. The kiln is programmed with a very carefully controlled firing schedule that takes into account the dampness of the mold, the type of glass being used, and the thickness & complexity of the glass and mold, as well as the number of molds loaded into the kiln, so that the proper heating, annealing and cooling phases will take place without cracking the mold or its glass form. Once the firing is completed and everything is fully back to room temp, the mold material is carefully devested to free the buried glass form inside. The glass piece then goes through a sometimes tedious process of coldworking to remove any plaster core materials, surface irregularities or flashing, and any glass overfills left in the sprue cup and sprue channels. For a more complicated hollow vessel form, this whole process of modeling, investing, firing, devesting & coldworking usually takes about 3 to 4 weeks, which is why kiln cast glass tends to be so expensive! The next time you see a piece of kiln cast glass by an emerging artist, just realize that they are likely not recooping much of the time invested in the piece, so have mercy when you see the price and just think, wow what a deal! jamie j mckay (emerging artist!) |
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