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Old 04-01-2005, 02:01 PM
Lani McGregor
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Lost: one COE thread. If found, please return to 1983...

My question at the start of this thread was “When/where did COE come to be synonymous with compatibility in the studio glass scene?”

I could have spared everyone the pain (ok, so some of you like pain) of English & Turner, Winkelman & Schott etc if I’d written MEASURED, not calculated, COE – since it is the measured COE that is nowadays claimed and generally understood to equate to the “fit” of different glasses. And – no arguments here? – we arrive at this COE (0-300C, or 25-300C, or 17-300C!) measurement via a laboratory test using a dilatometer.

Where do we find this – that the measured COE equates to compatibility - in the technical literature? Is there any mention in Scholes, Morey, Volf? If so, can someone direct me to it? We can’t find it.

Was matching COEs to determine compatibility EVER the practice of glass factories in the US or Europe? Not to our knowledge. We, and everyone else we know (thanks to Durk & David Hopper for input on the Europeans; thank you, Tom, for the notes on SPB history), have been doing compatibility testing based on thread tests, ring tests, Trident seal tests, bar tests, and chip/bar tests. None of those tests are measurements of COE or LEC.

Where the COE = compatibility thing IS found is in the book that Dan & Boyce wrote in 1983, while they still thought that matching COEs – or being fairly close – was critical to compatibility. They had reservations at that time and expressed them with disclaimers like “Coefficient of expansion numbers should be regarded as starting points from which to experiment rather than definitive numbers not to be questioned” and “…some glasses that have the same coefficient number, as determined by a laboratory, do not always fit each other when fused together.” (pg. 42, Glass Fusing Book One, 1983)

But in spite of those disclaimers, our industry (colored glass dealers and other manufacturers, and eventually users) grabbed this easy “code” and started using it to define compatibility. Terms like “Tested Compatible to 90.0” (even though the experts will tell you that you can’t even measure to a .0 of accuracy in a dilatometric test) and “90 COE glass” came to be accepted to mean “this glass will fit other glasses of this same COE”.

When Bullseye published its actual COEs that showed a COE (0-300C) range of 88 for our white and 91 for our clear, it was interpreted to mean that we allowed a mismatch of plus or minus 1.5 COE points. We never said that (but this also seems to have come down in the lore - note Pete's comment earlier).

When we declined to guarantee that our glasses would fit other glasses with a COE of “90” we were accused of trying to corner the market and refusing to be “cooperative” with other manufacturers.

The ball was rolling. Dealers were looking for easy ways to inventory, categorize and sell. (I remember the work that Therese did at C & R Loo to try to categorize compatible glasses. It was a supremely noble effort. But I can guarantee that she didn’t have COE tests run on those glasses. At $150 per sample, does anyone really think that Mr Loo let her spend that kind of money to find out what the COE of K61 was, much less the entire Kugler line? I suspect she called around and ASKED. If she then put COE numbers on the answers, it was pure speculation and trust in her sources.)

(apparently I’ve exceeded the ability of the blather-o-meter to track my rant at this point, so this is continued in the next post…)

Last edited by Lani McGregor; 04-01-2005 at 02:05 PM.
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