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Compatibility Testing

Glass incompatibility will show up as small cracks or fracture lines where the two incompatible glasses come together. These cracks will likely increase with time and may eventually result in a complete separation. The photo below shows an example of incompatibility.

Click photo to see enlarged photograph. Photo courtesy of glass artist Deb Compton.

Extreme incompatibility, such as that in the above photo, shows up fairly quickly (sometimes immediately )after firing.  More insidious incompatibility problems arenít obvious to the naked eye and need to be discovered through compatibility testing.

Although there are several commercially available  compatibility testing products (one of the earliest was called the stressometer), you can easily make your own compatibility testing kit.  All that's needed is a source of light and some polarized film.  A flashlight will work for the light source, as will a light table or even a bright window.  You can buy polarized film (sometimes called polarizing film) or you can use two camera lenses or even a broken pair of sunglasses.  Just make certain that the lenses or sunglasses are polarized, rather than simply shaded.

Once you've identified your light source and obtained some polarized film, you're ready for the compatibility test.

Click here for the next part of this tip, which discusses how to conduct a compatibility test.

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Copyright 2007 Brad Walker.  All rights reserved.

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