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Old 03-30-2005, 11:21 AM
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Pete VanderLaan Pete VanderLaan is offline
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Originally posted by Lani McGregor

And I’m talking measured (i.e. at 0-300C) not theoretical or calculated COE. Lots of people were doing calculations. But to our knowledge the practical testing done in factories on a daily basis has always measured the “fit” between glasses, i.e, the combination of expansion and viscosity – NOT the COE.
When did SPB first list a measured COE? I’m pretty sure that what Tom and Henry are talking about in terms of Labino’s formula is calculation.

Actually you have hit on the first point of confusion. How about 17C-300C instead. When I did the work at Los Alamos labs with this, we started at 0C just like the ASTM standard would have suggested. Nothing made real world sense. Once I shifted to 17C as a start point, things looked right. 17C is of course the temperature at which lab workers are comfortable while wearing white coats. I have to be very careful when I'm measuring four inch rods for expansion that the start temperature is consistent. In summer, it easily goes up to 23C so I need a cooling bath for the canes and dilatometer.

The labino stuff is calculation and it is consistent with the E&T numbers if run up to 250C ( I think). E&T did not originally go to 300C and that's why those numbers have never made real world sense. It seems to me it was either 250C or 225C. I cannot recall right now and I don't want to look it up.

When Croucher and I sat down about eight years back to talk about expansion we both felt that a 93-93.5 would have been a better standard but SP87( which is really a 96) was the elephant in the room. If we wanted to sell color that was not 45 percent lead we were going to target SP87. While Kugler just got around the fit issue by dumping lead into the glasses, we really wanted lower lead contents wherever possible and no lead if it was not critical to the glass. Kugler and company all use GLASMA 70 or 71, I forget which but it is their proprietary batch. It has a predetermined L.E.C which they add colorants to. It explains why Kugler is all over the map. John and I both made the color first, and then adjusted the glass to a 96.

I agree about the multiple formulas. I have six base glasses. I think John had seven the last time we talked. The trouble with the viscosity issue is that I can't explain it. Nick couldn't explain it. Why did lead seemingly defeat the compatibility problem up until you pierced the surface tension of the piece with a saw or a grinder? Would a high Bismuth glass do the same thing ( moot since bismuth is too expensive).

I don't think anyone listed an L.E.C. on their stick until Croucher. I never did. I advertised its expansion but never put it on the rod. I liked the parrots too much.

Maybe glassblowers are more like the tarot card of the fool. Walking towards the cliff and always the presumption that they will turn at the last minute without ever knowing the cliff was there.
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