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I have read this question:

Why doesn't diamond glow when hot?

This is because of Kirchhoff's law of thermal radiation. The corollary from it is that emissivity of a material is equal to its absorptivity.

enter image description here

Does any material glow, under appropriate conditions?

a body must absorb and emit identically at a given wavelength. Transparent is a terrible emitter.

These answers specifically explain that though every objects glows in a sense when heated (just some not in the visible range), in the case of diamond, heating it will not cause it to simply emit visible wavelength photons.

Thus diamond will not emit visible light, since it is remaining transparent when heated, and can only emit little number of visible wavelength photons.

Though, this explanation does not work for glass. If you heat glass, it emits visible (glows), meaning either of two things:

  1. it absorbs visible and re-emits visible

  2. it absorbs all wavelength and re-emits visible (in cascades or for other reasons changes the re-emitted photons' wavelength relative to the absorbed ones)

Question:

  1. Why does hot (molten) glass glow, while diamond does not?
Qmechanic
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Árpád Szendrei
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1 Answers1

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Clear glass does not glow all that much in the visible. The illustration seems to show quite thick glass, and it is impossible to see from the image whether it is clear when cooled down. The temperature would be quite high (1000 °C or more), an opaque object at the same temperature would radiate more.

Edit: an image from https://youtu.be/FXXwCNSiAFY Hot glass, Noomoon Pictures