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Molten glass, on photos, appears to radiate light like a black body. However, as cold glass absorbs almost no visible light, I would guess the emissivity for visible light is very low. So I am wondering, is the emissivity of molten glass surprisingly high, or does molten glass emit far less light than a black body?

[ -- edit: I am mainly interested in the emissivity for visible light, not infrared ]

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Surprisingly high. These tables says the emissivity of molten glass to be between 0.76 and 0.94

https://www.calex.co.uk/site/wp-content/uploads/2015/07/ir-in-glass-industry.pdf

https://www.sika.net/images/Documents/Table_of_Emissivity.pdf

http://www-eng.lbl.gov/~dw/projects/DW4229_LHC_detector_analysis/calculations/emissivity2.pdf

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  • $\begingroup$ Thanks for the links. Those tables report the emissivity for infrared thermometry, and it seems only one of them contains data about molten glass. Cold glass is not transparent for infrared (if λ>3 µm). I am mainly interested in the emissivity only for visual light. $\endgroup$
    – jkien
    Jan 2 '19 at 19:53
  • $\begingroup$ This paper is pretty good: The Emissivity of Transparent Materials, R Gardon (1956) doi.org/10.1111/j.1151-2916.1956.tb15833.x Talks about how the emissivity is just not a surface property. $\endgroup$
    – D Duck
    Jan 3 '19 at 19:25

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