I’ve got a brilliant vet. She’s coming to our home to help Ed “pass over”. I wish there were a glass doctor who’d do the same thing for the sick old myth of the COE.

Fat chance. This misunderstanding about compatibility and the Coefficient of Expansion has been around for longer than many people have been fusing. They were raised on it. Sadly, it may be around forever, mucking with basic technical information in our field and making it harder for users to solve problems when they occur.

We’ve never labeled Bullseye glass as “90 COE”. At the beginning, we labeled the sheets – and still refer to them today as – TESTED COMPATIBLE. Due to the confusion that arose when other companies entered the market and adopted the term we’d coined, we now label our sheets BULLSEYE COMPATIBLE. My two earlier blogs in this series define exactly what this term means.
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Sorry to be dragging my feet on this subject. I have to confess to finding it a little tedious. For me, technical information is like lifeboat maintenance on the Titanic. No one really cares about it (myself included) until something goes wrong.

Then you’d like to know that the equipment doesn’t have holes in it.

Last week I went over basic compatibility testing as it was established at Bullseye and has been practiced in our field, with little or no variation, for the last 25 years. Whether that test is being performed within the factory or the artist’s studio, it is not - and never has been - a measurement of the so-called COE. What is measured is the strain that exists at the interface between the chip and the base glass.

WHAT STRESS?! By Bullseye’s factory standards the four chips on the far right of this bar are considered incompatible. Chips 1570 and 1572 are low relative to the base clear. Chips 1573 and 1580 are high relative to the base. Compare this bar with one in which many of the samples are very obviously out-of-compatible range
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Third, and last, on my list of “Unbeautiful Things” is the manner in which kilnforming is being marketed today. I have some pretty strong opinions on this, so if you’re not ready for another rant, you may not want to keep reading.

This is what STRESS looks like. It happens when glasses that are not “compatible” are fused together. Understanding it is the foundation of glassforming.

IMO reducing a rich and fascinating field to a litany of assurances that success will come from buying a glass with a “wider margin of error” and a kiln that a dog can program does a disservice to the many exceptional artists who have worked to advance the reputation of the medium and to the beginners who deserve to be educated, not harvested.
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