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Mixing Green Beans with Brown
Part Five of a Five Part Tutorial on Fusing and
Compatibility
Click here to go to the
first part of this article.
To test for
compatibility, you must fully fuse small pieces of the glass you'd
like to test. The simplest, but not necessarily to
best, way to do this is to place one scrap of a glass you want to
use on top of a slightly larger scrap of another glass, and then
fully fuse the two pieces in your kiln.
This will
work, but a better way is to use a base glass of a known COE, and
test your scraps to see if they work with the known glass. To do
this, cut a strip of the base glass 1 1/2" in width and several
inches long. For each other glass you wish to test, cut a small
square (about 1/2" by 1/2"). Place the test squares one-inch apart
on the base glass. Fuse flat to around 1500 degrees Fahrenheit, then
anneal and cool.
To
conduct the test, you simply sandwich the already-fused piece of
glass between the two pieces of polarized film and hold it over a
light source (such as a light table or a flashlight). Rotate the
lenses so that they are at right angles to each other and as little
light shines through as possible. Now check the edges where the
different glasses come together for a white glow. The brightness of
this glow will determine the severity of the stress and the degree
of incompatibility.
If
there's no glow, or only a very slight halo, then the glass can be
assumed to be compatible. Greater amounts of incompatibility (as
shown by more and more light coming through the polarized film)
means that the piece may be useable, but that it's more likely to
crack with use. Remember: where there is light, there is stress.
And stress is what causes the cracks.
There are
a couple of limitations to compatibility testing. The most
significant is that you can't use this method to test with two
opaque pieces of glass, you have to have some transparent so that
the light can get through. That's why testing with a base clear
glass is highly recommended.
A second
limitation is that it's unrealistic to expect to test every single
scrap of glass you have sitting around. Instead, you have to test
the larger pieces, or the colors you most want to use in a fused
project. Save the other scraps for non-fused projects.
And be
careful when you mix green beans with brown. You don't always get
what you want.
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Copyright 2005 Brad Walker.
All rights reserved.
This article was originally
written in 1999 and was one of a series that 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.
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