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FIRING THE KILN CASTING

The process of firing the casting is basically the same, regardless of whether you fill the mold using loose frit, pate de verre or a crucible drip. In general, you follow the same basic procedures and steps as heating for fusing and slumping, except that the thickness of the glass and mold generally dictate slower heating and cooling times. It's also very important to recognize that the mold can crack during firing, so extra care should be taken to ensure that everything stays intact.

A good rule of thumb for how fast to heat is to increase the temperature around 300 degrees per hour for each inch of the casting. It never hurts to go slower than this, and you can sometimes go faster, but faster heating schedules run the risk of thermal shocking the glass or mold.

It's generally a good practice to soak for half an hour or so at around 1200 degrees F, then continue more rapidly until full fuse temperature is reached. For ordinary soda-lime glass (such as Bullseye and Uroboros) this is around 1500 degrees F. Some artists prefer to soak at a temperature as much as 100-200 degrees F above full fuse; there are literally hundreds of different ways to kiln cast - the right one is the one that works for you.

Once the casting temperature is reached, the casting needs to soak for a while. How long depends on the thickness and shape of the mold and the size and complexity of the item being cast. You'll need to experiment to find the right length of time (start with half an hour to an hour for a simple casting). Take comfort in knowing that you can re-fire if necessary. In addition, you can always soak a bit longer than you think you need to just to make sure.

If you need to add more frit due to settling, just turn off the kiln, add the frit, reheat to soaking temperature, then soak some more. This process can be repeated several times if necessary. 

Click here to go to the next step in the Kiln Casting process, "Annealing and Cooling."