One of the things about recycled glass that everyone who uses it knows is, you have to test everything. Twice. And then do it all over again, since your results could have been a fluke and the worst time to realize that is after you’ve spent a very long time on something.
So. In preparation for some cast sculptural work that’s coming up, I decided to do some potmelt (crucible) casting tests. The factors I need to isolate are: glass particle size, aperature size and temperature.
The most obvious way seemed to test three aperature sizes and three glass sizes at the same temperature. This would allow me to isolate one factor at a time.
The glass I used was: ground clear window glass larger than 16# and smaller than 1/8″, ground clear window larger than 1/8″, smaller than 1/4″ and large chunk tempered glass. All three were mixed with one third by weight of ground Bombay Sapphire bottle glass.
Next I used 9 terra cotta pots, all of the same size, drilled 1/2″ holes in the bottom of three, 3/4″ holes in the bottom of three and 1″ holes in the bottom of three. Next step; loaded one of each size with one of each glass mixture.
I set them all up in my side-fire kiln (a.k.a. the EZ bake). Based of past experience, I knew that 1700 wasn’t hot enough. I decided to try 1850 for 15 minutes.
This pot contained the smallest particle size (16# mesh) and the smallest aperature (1/2″). This is very useful, because it gives me a baseline for the bottom end of the success spectrum.
The next step is to look at the resulting melts and see which other combination would suit our purposes the best.
Fusing and casting with mixed glass of unknown COE without extensive testing is not considered best practice in the glass world. An article in Boyce Lundstrom’s seminal glass casting books about creating glass with a new unique COE by melting together various glasses made me wonder if the same process could be true with pot melts. Unfortunately, the tendency of the bottle and float glass to be become opaque during the pot melt process made it quite difficult to judge the degree of internal stress when inspecting the results through polarized film:
For more information about mixing glass for fusing, and how to look for internal stress: