In this particular case the "manufacturers specifications" say there's more to compatibility than just COE, so your statement contradicts itself. And I'm not quite sure why you equate "marketing" with "lying." Marketing is not (usually) an evil plot to hoodwink customers. In fact, educating customers is generally considered more a effective marketing strategy than lying to them, as you seem to imply that this particular manufacturer is doing.Lynne Chappell wrote:Oops, hit a nerve. I guess it was the tone of the remark. I guess I just get tired of hearing the same response from Bullseye whenever anyone names a glass by its COE. And excuse me if I find that that particular response smacks of marketing. (Don't use the other guys glass just because it is supposedly the same COE, it hasn't been tested against our glass.) And I hope Lani isn't reading this thread because I'm actually a great Bullseye lover. I use their glass almost exclusively, use it in my classes, and sell it in my store.
However if you will only use glass that has been tested with the chip test you can only use Bullseye glass without your own testing, which is pretty limiting. As for different viscosities playing against each other: if you test glass A against a clear standard, and glass B against a clear standard, the assumption is that they are compatible. That is what we do with a chip test in our studios and that is what Bullseye does. I don't see that it is reliably testing one colour against another if there are subtle other factors such as viscosity involved. Perhaps the viscosity differences that play nice with the clear won't play nice when you put glass A with glass B without the clear?
I know that Europeans use Bullseye with GNA with a 2-4 point difference in COE, but I believe that the method of layering is instrumental in keeping the stress from cracking the piece.
And I have never heard of 90 COE float - where is that coming from? All the float that I have ever seen was in and around 83.
I've had Spectrum System 96 pieces develop compatibility cracks. I've had a piece for 15 years that has Bullseye and Spectrum glass mixed together that is still intact. Its a fuzzy science.
I think people should be content to trust the manufacturers specifications and feel free to use glasses with the same COE without fear. If you occasionally get a crack, well that's just the nature of the medium.
Have you ever asked yourself why some of this "fuzzy" stuff happens? WHY can "Europeans" layer BE with GNA to keep "the stress from cracking the piece?" If your Spectrum 96 develops "compatibility cracks" despite having the same COE...why? If BE and Spectrum 96 combine successfully in a piece, despite COEs that would suggest otherwise, why? Logically, if these things are possible then there's something besides just COE at work. And, equally logically, if those factors can make glass work together, they may also prevent glasses from combining successfully.
Glass is an important substance, studied extensively, and there is a great deal of readily available information out there that can solve these puzzles. The manufacturers are one source, the Web is another, and places like Rakow bend over backwards to provide information (I just got 75 pages of information on potential devit issues in casting tonight from Rakow, in fact).
I think we can do better than a virtual shrug and "well that's just the nature of the medium."