Oh it's glowing all right at those temperatures. It's just clear. Now if you get a layer on the surface, even a very thin one, of something that reacts with the atmosphere, and it will go opaque because of the reacting compounds at the surface. Tin bloom on float glass, applied color or additives, nasty polluted kiln atmosphere from previous pottery glaze use, etc. will cause the surface to become rather opaque to some degree. Good clean clear glass though is always clear at process and furnace temperatures. I suppose if the background behind the clean glass is dark, then the glow might overwhelm what you actually see and it could look opaque, but it is still clear. Get some light behind it and it becomes readily apparent.
R. > -----Original Message----- > From: Stephen A. Lawrence [mailto:sa...@pobox.com] > Sent: Monday, July 27, 2009 6:57 AM > To: vortex-l@eskimo.com > Subject: Re: [Vo]:Question about hot glass > > > > Rick Monteverde wrote: > > The hot (1800+ degF) and warm (1450+ degF) glass I've worked with > > always stays clear. Glass from a furnace is extremely > clear, you can > > look at the bottom of the pot and it looks like there's > nothing in there. > > In this case it's presumably also not glowing, or at least > not much, and that would seem to fit with the claim that it > absorbs just as it radiates. > > > > > > The really weird thing is when gold metal gets translucent. > Noticed it > > for years but never believed my eyes were telling me the truth. > > Say what?? Could you please provide more info on this? This > teaser is a killer! > > > > > > R. > > > >> -----Original Message----- > >> From: Stephen A. Lawrence [mailto:sa...@pobox.com] > >> Sent: Wednesday, July 22, 2009 3:38 AM > >> To: vortex-l@eskimo.com > >> Subject: [Vo]:Question about hot glass > >> > >> I ran across an explanation of a "blackbody" which I actually > >> understood a week or so back (totally unexpected, it was in the > >> introductory chapter to a QM book), and since then I've > been fiddling > >> around with gedanken experiments involving black boxes with little > >> holes in them and the second law of thermodynamics. > >> > >> And it appears to me that, according to the second law of > >> thermodynamics, if glass is heated red-hot or orange-hot, and it's > >> actually seen to be glowing orange, it should also turn > >> *opaque* to visible light while it's at that temperature. > > >
