Well, I started crafting an argument to counter that, but in the middle of writing it I had to confirm I wasn't talking out of my ass. So I went and found the article that quote came from. http://www.glassnotes.com/resources/Does-Glass-Flow/Glass-Flow.pdf I'm still skeptical. The only thing he argues to refute glass flowing down and becoming thicker over time is anecdotal evidence of someone claiming they have seen examples of old glass being thick at the top not just the bottom. The rest of the math isn't sourced well, as this is more of a casual piece. But he claims, >"Estimates of the viscosity of glasses at room temperature run as high as 10 to the 20th power (poises; a unit of measure for viscosity...) >"It is worth noting, too, that at room temperature the viscosity of metallic lead has been estimated to be about 10 to the 11th power, (1011 ) poises..." He finishes his argument with, > Presumably, then, the lead caming that holds stained glass pieces in place should have flowed a billion times more readily than the glass. While lead caming often bends and buckles under the enormous architectural stresses imposed on it, one never hears that the lead has flowed like a liquid. I'd argue the viscosity rates he mentions are theoretical estimates just as he claims, not measurements (since you can't manifest that many years of data,) and are questionable. He may have a single anecdotal example of glass being thick at it's top, but there are plenty of documented cases to counter that. Furthermore, his comparison of metal caming (glass frame) warpping under structural stress to that of glass accumulating mass toward gravitational forces over time doesn't make sense. I'm willing to bet, that if you were to put a sheet of glass in a true: zero gravity, zero atmosphere, standard temperature, totally isolated chamber; if given enough time the intermolecular forces would form a sphere, or other more tightly wrapped shape. While a rod of iron would not change at all. I'm not post grad educated, but I have had enough experience with people who are to know their degree or title doesn't make them as smart as most would believe. Despite him being a research scientist for the Corning Museum of Glass for 40 years, that doesn't mean his opinion on the minutia of chemical properties is absolute. IF it's true that solid objects have a viscosity under normal forces, than this seems to me to be a somewhat esoteric argument as to the transition point of liquid to solid. As far as I am concerned, if there is a noticeable flow within the lifetime of a normal man, than it is liquid. Thank you for showing me this. I spent way to much time on contemplating this and typing all this out, but it's interesting.