Stephen A. Lawrence wrote:
> I've seen lead-crystal (very clear) glass being worked at high > temperatures, at Corning many years ago, and as far as I can recall it > did indeed glow bright orange. > After the conversation here I searched through my old slides and found a photo of what I remembered. Turns out my memory was wrong -- the end of the metal rod, clearly visible through the (transparent!) hot glass, was glowing *bright* red. The glass itself was glowing *dim* orange (dim by comparison with the rod's glow). The rod and the glass must have been at about the same temp, or more likely, the glass was hotter than the rod, as the glass had been in direct contact with the environment of the furnace while the rod was "protected" from it by the glass. Guessing the rod is steel but I don't know for sure. Anyhow a blowup of a small piece of the original picture is attached. It's a scan from a slide, which was shot in dim light and wasn't super sharp, unfortunately; it's been despeckled and unsharp-masked heavily but still looks a bit fuzzy. So it looks like hot glass doesn't go particularly opaque, but also doesn't glow very brightly at all in comparison with metal. The "double image" is due to a reflection: the glass knob, on the end of the rod, is being rolled along a very smooth, shiny surface to give the shape the glass worker wants. This was the Steuben workshop, where they mostly made blobby animals and things like that, so rounded knobby shapes were kind of the order of the day.
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