Warm Glass
REMOVING AND CLEANING THE CASTING
Once you are certain that the mold and glass inside are cool, carefully break the mold away from the glass. Proceed slowly, taking care not to break the glass. This can be easier said than done, but if you are careful you will eventually be able to remove the entire mold and free the glass.
The surface of the casting will probably look ugly, not at all like the shimmering piece of glass you may have imagined. Let the casting sit for a few hours just to make certain it has completely cooled, then you can begin the cleaning process.
Wash the casting in water. You may want to use a stainless steel or stiff nylon brush to clean off the mold material residue. Sometimes you will need to use a wet/dry sandpaper or Dremel-type tool to help with the cleaning. It’s important to keep the casting wet during this cleaning and to wear a respirator to keep from breathing in any silica dust particles.
Once the casting is clean, you may want to polish it (see Polishing equipment section) or shine it up using an oil or acrylic enamel. Clear spray oil, such as Varathane Natural Oil Finish #66 Clear, will permanently give the casting a shiny finish. Similarly, you can use a clear acrylic or enamel spray to give the glass a permanent wet look. For all of these products, make certain the casting is completely clean and clear of fingerprints and other blemishes prior to using.
If you have a soda-lime glass such as Bullseye or Uroboros, you can use a commercial product such as Back Magic to impart sheen to the casting. These products are painted or brushed on the casting, which is heated in a kiln to around 1100 degrees F. If you use this approach, make sure you heat, anneal, and cool the item slowly so as to prevent cracking. Unfortunately, these products are lead-based, so they can not be used on surfaces that will come into contact with food.
Finally, although kiln casting can be more rewarding and interesting that fusing and slumping, it is also more complicated. There are many more tricks and techniques, and most artists have developed their own approaches to kiln casting. This variety can be a source of frustration (there is, after all, no single "right way"), but it is also part of what gives kiln casting its charm and excitement.