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The Creative Can of Beans
Part Three: Cooling the Can
This is part three. It
probably won't make sense unless you've read parts one and two.
Click here to start at the beginning.
Once you're happy with the way the glass has
slumped over the can, you can stop soaking and begin the process of
cooling down. If you can't see enough through the peephole to know
if you're happy or not, don't worry. It takes a little practice to
know just the right amount to soak. Even more, scrap glass is
cheap, maybe even cheaper than empty bean cans. The great thing
about working with kiln-formed glass is that you can learn with
inexpensive materials. An even greater thing is that you can
salvage a lot of your mistakes by firing again later on.
To begin the cooling process, you should stop
heating the glass and let your kiln cool quickly from your slumping
temperature to around 1000 degrees Fahrenheit (around 525 Celsius).
Some people "flash vent" their kiln, or open the lid for a few
moments, to make the glass cool quicker, but this isn't usually
necessary. Most kilns will cool fast enough on their own.
You may have heard people talk about
"annealing" glass. That's just a fancy way of saying that you need
to control the way the glass cools to help relieve stress in the
glass. If your glass has too much stress, it can crack when it
reaches room temperature. The larger the piece of glass, the more
critical proper annealing becomes, but it's still important for even
bean-can-sized pieces of glass.
There are several different types of
annealing. One is to soak the glass at the manufacturer's
recommended annealing temperature for a while, and then continue
cooling it to room temperature. Many tables are available that give
the appropriate annealing schedules for glass from major
manufacturers of fusible glass.
Another type of annealing schedule can work
well when you don't know the exact type of glass or the
manufacturer's recommendations. Rather than soaking for a while,
this involves just cooling the glass steadily and slowly from 1000 F
to around 750F (540 to 400 C). This range is broad enough to allow most types of
glass to be annealed, and no annealing chart is required.
Whew! Annealing sounds complicated, but so did
making a good baked bean casserole the first time. For small items
like the bean can, just let the kiln cool slowly. Keep the peepholes
plugged and the kiln lid closed, and your kiln will most likely cool
slowly enough to allow for proper annealing. Just check to make
certain that your kiln naturally cools more slowly than about 200
degrees per hour Fahrenheit (125 Celsius) from 1000 to 750 Fahrenheit
(540 to 400 C). If your kiln
naturally cools more slowly than that, then consider yourself lucky:
slower works nearly every time. If your kiln cools too fast (it
almost certainly won't), then just heat a little bit to slow down
the rate of temperature decrease. This approach will work well for
smaller pieces; there are other ways to anneal that work better for
larger items.
But more about that later, when we discuss
further adventures of the bean. For now, just wait
for the kiln to cool to room temperature. (Sometimes it's a good
idea to just go to sleep and let the kiln cool overnight.) When the
kiln's good and cool (resist the urge to peek), open the lid and remove the can with the slumped
glass on top. It should be cool enough to handle without gloves.
Carefully separate the glass from where it draped around the can.
You may need to twist slightly, especially if the bottom of your can
was a bit rough, but the glass usually comes loose without too much
trouble. The fluted form you're holding will make a perfect vase.
If you don't have any flowers, try putting a small candle in it and
enjoying the flames as they flicker. Or just the display the glass
piece on a mantle.
The can will probably look crusty and maybe a
little worse for wear. Kiln wash may be flaking away. If you want,
you can clean the can, reapply the kiln wash, and fire again. Or
you can just toss the can and get another one from the pantry.
(Beans for supper again?) You can even, now that you know the
basics, try slumping on different shapes and forms. Steel cans work
best, but some other cans will work, too (but not aluminum, it melts
at 1200F/650C). Just be careful that if you slump inside the can
(instead of outside it) you only use very shallow metal items like a
small bowl (no
cans). It's also a good idea to drill a few small holes (1/8" or
smaller) in the bottom of your mold to let the air escape so the glass can slump
all the way.
You can even use ceramic items like terra cotta
pots and plates. Unglazed or "bisque" pottery is best, but you can sand the
glaze and apply kiln wash anyway. Slumping inside pottery works
better than slumping on the outside (the opposite of steel), but
make sure you drill those holes and remember to apply kiln wash
before you slump. Or, if it seem to much trouble to make your own
molds (tired of eating beans?), commercially made stainless steel
and ceramic forms are available.
That's slumping glass in a nutshell (well,
actually, it's in a can of beans). Stay tuned for future bean
topics -- the next one (coming soon!) is on fusing pieces of glass
together to form a solid sheet. Then we can slump those sheets and
add even more color (or is that colour?) to our bean can shapes. In
the meantime, save your glass scraps.
And eat plenty of beans.
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Copyright 2005 Brad Walker.
All rights reserved.
This article was originally
written in 1999 and became the basis for the
Warm Glass website. It
has also been published in Common Ground: Glass, the
newsletter of the International Guild
of Glass Artists. There are at least two more lengthy parts, all coming
soon to a computer near you.
If you want to learn more about
fusing and slumping glass, check out the Warm Glass tutorial at
www.warmglass.com/basic.htm
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