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