Ditmar/Gayle on sun 1 aug 99
The heavy crazing, aka: cracking, of glass in the bottom of bowls or on the
surface of other clay pieces is due to incompatibility between the two
materials.
For the thin layer usually produced, normal kiln cooling is generally
adequate for proper annealing. Up to 1/4 inch or so would anneal with very
little extra time to cool down. The annealing isn't the problem here.
When working with glass, the COE or coefficient of expansion, is the most
critical. You can't even melt different brands of glass together without
the item cracking, unless the COE is the same. The uneven shrinkage of the
two materials puts such a strain on the glass that it shatters in place.
There is too much of a difference between the COE of glass and ceramic to
have it in a clear, crack free pool in the bottom of a vessel.
Sorry to rain on your parade, I wish there were an easy solution. I've
often wanted to do the same thing whenever I look at the vivid colors in my
scrap pile.
>From Alohaland, Ditmar.
Jeff Ferris on wed 4 aug 99
I have been playing with melting/fusing glass with ceramics a bit... just
playing so far.
My try I just placed some chunks of stained glass, bottle glass and
window glass onto a piece of bisqued fired stoneware, fired to ^6 and let
cool normally. Wowie! What color and depth! And where I stacked different
colors of glass, the cooled glass captured the fluidity of the glass'
metled state. Kinda like when you put a drop of food color into water and
you watch the color drop into the depths of clearness? BUT, I had to
touch... OUCH! Little slivers of glass into my finger tip!
So I placed the pieces out of reach. Like a moth and a bug zapper, I was
drawn to the color, depth, motion and gloss. So I kept playing and
getting zapped. With bisque temps, ^10 and even in the raku kiln. If the
crazing is OK for you, I have learned that if you put a clear glaze over
the pieces of glass, then at least, for me, the surface seems
finger-safe. Nice, smooth surface over a crazed pool of glass. (I have
been doing a lot of high-relief tiles and been looking at ways to fill
the recesses to create a smooth surface and maintaining the visual
relief.) None of my tests are more than a few months old, but they don't
seem to be getting more dangerous as time passes.
Something else that is cool about glass is that it takes surface
impressions very well. On one tile, in the raku kiln, covered with glass
& glaze, I tried to reduce in-kiln. So, when I reached temp, I grabbed a
big chunk of straw, turned off the gas, opened the lid, tossed in the
straw and quickly closed the lid and all vents. Each strand of straw that
hit the tile top, left a deep grove. Like the texture in the glaze
surface when you put straw in the reduction bins, but much more
pronounced.
I have a friend who likes to place small chunks of glass near the top of
her teapots and do the normal ^10 firing. The glass melts, runs down the
side of the pots to form a very thin streak and it does not seem to
craze, due to the thin spread of the glass.
I read somewhere (digitally) that if copper is placed under the glass,
some really great colors result. My next firing will have a few small
vessels with copper wires and foil beneath my glass and glaze.
Finally, some time ago, I ran across a web page about someone doing
glass-casting and it detailed the firing schedule used. You'll have to
search for that yourself!
So, I have yet to produce anything saleable, but at least I don't bleed
anymore.
-- Jeff Ferris
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"You're gonna have to kill me to make me stop." -- Cool Hand Luke
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