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Mixing Green Beans with Brown

Part Four of a Five Part Tutorial on Fusing and Compatibility

 

Click here to go to the first part of this article.

If you don't want to buy glass that the manufacturer has already tested for compatibility, then you'll need to do the testing yourself.  This isn't difficult, but it does take a few special tools and a little time.  Testing is the only way to know for certain that the scraps of glass you have will work together without causing cracks.

Testing for compatibility requires a kiln, some scraps of glass to test, and some polarizing film.  Of these, the film is the one that's unfamiliar to most people.

Polarized film is a special filter that blocks a portion of the light coming to your eye.  Polarized filters are often used in photography to reduce glare from water or heighten the contrast between clouds and the sky.

They're also used in Polaroid sunglasses, or in sunglasses that are “polarized” but may not be made by the Polaroid company.  (The Polaroid company, now better known for instant cameras, got its name when founder Edward Land discovered a new way to make polarizing filters and used it to make sunglasses and similar products.  Needless to say, Dr. Land probably managed to stay awake during his high school physics classes.)

I found my first pair of polarized lenses by going to my local drug store and checking out the sunglass display.  I was looking for a pair of sunglasses that was polarized and asked the clerk for the least expensive pair of polarized sunglasses they had.  We eventually found a broken pair that was stashed behind the display.  After haggling on the price (we agreed on free!), I checked to verify that the lenses were really polarized.  This is done by stacking two lenses on top of each other and rotating one lens while holding the other one still.  If the lenses are polarized, you will see the amount of light that comes through change as the lens is rotated. When one lens is 90 degrees from the other, almost no light will pass through.

Once you've found a polarized lens, you're ready to start compatibility testing. 

Click here for the final part of this series -- how to do the compatibility test.

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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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