Recycled Glass Pot Melt Tests

Flash back Friday! Here’s a post from the archives that is still pretty entertaining! (Post was first published on 2/8/2010)

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.

Recycled Glass Pot Melt Tests Set Up

Recycled Glass Pot Melt Tests Set Up

Here are the pots post firing (the bottom shelf, the remainder were on another shelf).  With the exception of that center pot, it looks like we got pretty good drainage of the crucibles.  The center pot:
Recycled Glass Pot Melt Test

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.

Recycled Glass Pot Melt Test

Recycled Glass Pot Melt Test

This is the smallest particle size (16#) through the 3/4″ aperture.  The result is shiny and smooth, but not translucent.
Recycled Glass Pot Melt

Recycled Glass Pot Melt Test

Med size (>16# <1/8″) clear through the 3/4″ aperture.   The results are very shiny, with some translucency.
Recycled Glass Pot Melt Tests

Recycled Glass Pot Melt Test

Large chunk (~1/2″) tempered glass through the 3/4″ aperature.  Very translucent and shiny.
So, the conclusion here is that we need to use about a 3/4″ aperature or larger.  Any of the glass particle sizes will work with that aperature, but each gives a very different result.  Next step in the casting process is mold making and further temperature refinement based on increased quantity of glass.






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