Saturday, October 24, 2009
What does a casting look like after firing? Removing the plaster and excess glass.
As I mentioned earlier, the recycled glass is kiln-cast in plaster and silica molds. After firing and cooling, the plaster will easily crumble away from the casting. Sharp glass edges may remain on some of the casting so wear gloves.
Most castings do not come out perfect and a lot of cold working must be done. I first use use my glass grozier pliers which is a hand tool for removing away small excess bits of glass. Since you have to estimate how much glass to stack in your mold, excess glass can flow around the edges of the mold and this glass can be nipped away. If the glass is too thick, it will have to be cut off with a wet tile saw or glass saw (electric).
The casting has to be wet scrubbed with a variety of brushes to remove the plaster bits embedded in the glass. Any pointed tool will also work in picking out bits of plaster. There will still be some pinpoint plaster bits remaining so the casting can be soaked in a variety of substances. I have had some luck with Coca-cola which acts to fizzle the plaster out of crevices. Lime-Away can be used as well but since this is a toxic chemical, wear gloves and do not leave it unattended where children or pets may have access to it. Some chemicals can create an etched effect so be cautious in testing different chemicals if you do not want to achieve that effect.