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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.


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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