If You Can Sculpt It, You Can Cast It.

Casting glass consists of four main steps. The first step is to sketch out a design and scuplt it. There a number of different mediums from which you can sculpt the primary positive. One of the more common methods is to use a large block of wax. This allows the artist to shave away layers from the piece as well as add lumps of wax back onto the positive. Once the rough positive sculpture has its general form, finer details can be added using a light flame to smooth out the surface and remove any unwanted lines or texture.

Once the positive is complete, a negative is made using compacted sand or plaster of paris. If proper planning is done, wood can also be used as a mold. In the case of sand or plaster, the wax is inserted into the material and is left to set. Once the sand or plaster has hardened, the wax can be removed by melting it with either a torch or steam. A caution to the artist: be careful to avoid small crevices or fine details as the glass may not be able to fill these pores before it becomes viscous again.

Now the fun begins. While the mold was being assembled, a pot of glass was being brought up to temperature in the furnace. Once the glass has melted and the bubbles and strings are removed, it is ready for pouring. Unlike glass blowing, though, the temperature of casted glass is a little higher. The elevated temperature allows the glass to reach all areas of the mold and fill in the smaller details that may have been incorporated into the design. Generally, the mold is created with a number of holes on one side depending on the size and intricacy of the piece. The molten glass is poured through these holes and the mold is gently tapped to ensure that the material has filled the entire form. The trick to pouring the glass into the mold is to avoid trapping air.

The final step may be the trickiest part. Since glass is an amorphous solid it has a number of weird properties. Among these is its coefficient of thermal expansion. Upon cooling down from the elevated temperature, glass can shrink up to 17%. This creates a large amount of stress throughout the piece and can lead to small cracks or even catastrophe. To acount for this misfortune, the entire mold needs to be annealed. Annealing is the process through which a piece is brought down to room temperature in stages. For each piece, this cycle may vary as the thickness and size of the overall piece will be different. Once the piece has reached room temperature, the form can be removed from the piece and the glass sculpture can be touched up in the cold shop.