Floating Away

Been quite busy lately and haven't had time to post.  A while ago, I posted about some float (window) glass that a buddy of mine obtained quite cheaply.  You can follow that thread here and the first test results here.  I certainly was amazed by the results which wasn't at all what I expected.  I posted my results and asked some questions over at the Warm Glass forum.  The answers told me that I should have expected the results.  But I wasn't happy.  The holy grail of cheap clear casting glass was theoretically in my sights and I wasn't giving up quite so easily.

Off to the kiln for round two.  Since the first test wasn't flat, and took way too long to grind, I decided to fire the test piece longer and hotter.  The test pieces are 8" rings about 1" thick.  This is something that easily fits in my little kiln, doesn't take forever, and is easily repeatable.  I doubled the length of time for the melt and added 150 degrees to the top temperature.  Glass I'm used to would have been in a puddle on the floor at those times and temperatures.  Here is a picture of the second test.

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Now this is strange.  It's hard to see in this picture but the glass went completely milky white.  The previous piece had "veils", but this piece is completely opaque.  It was definitely flatter, but certainly isn't smooth.  The bottom was pretty good, but this still has a long way to go before I could say I have an 8" flat disc.  My guess right now is that even longer/hotter wouldn't get where I want to be.

That left another test to do.  What if I took the glass, crushed it into frit, and then cast that.  That is a good way to work with other types of glass.  So I put a bunch of the float cullet in the kiln, heated it up to about 1100F, and then quenched the hot pieces in a bucket of water.  This sets up a bunch of internal fractures in the pieces, but they don't shatter immediately.  Hitting them with a hammer creates a fairly uniform gravel (frit).  The best way to describe it, is that they are like fat grains of rice. 

I weighed the first test piece which was 2.5 pounds.  I then weighed out the same amount of the frit, so I'd have a good comparison.  Of course, the frit mounds up as there is quite a bit of air spaces in between each of the grains.  It should all melt down flat.  Off to the kiln with a schedule that I thought would work, based on previous frit casting.  Boy was I surprised.

The picture is sort of out of focus, so sorry for that.  But you get the idea.  This looks like the surface of piece of sandpaper enlarged a hundred times!  This isn't flat, not even close.  However the color is much more uniform, even if it is white.  That I expected based on previous frit casting with transparent glass.  I wasn't ready for the surface texture.  Longer and hotter for this piece is needed as well.  

Finally, I had a friend polish the first test piece.  This is quite nice.  I like the veiling effect, but you certainly see the shape outline of the original cullet.

Well, its off to consider other options and tests.