[Jewelry making - Article 00025] - Re: [Orchid] To quench or not to quench, that is the question

[James Binnion]

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Hi John,

>     Second - if you heat something up hot enough, it glows - "becomes
>     incandescent". The colors of temperature have been known since the
>     before dark ages, and are well defined. If you are heating copper
>     or gold, the reddish color of the metal can fool the eye, but
>     that's only light. If you heat a piece of steel, a piece of copper
>     and a piece of glass all to 1500F in a dark room, they will all be
>     roughly the same color, because it's not color, it's incandescence. 

    To continue to beat the dead horse. 

    The color that heated objects radiate is a little more variable than
    you suggest. There is the "ideal black body radiator" that will
    radiate a specific spectra when heated to a specific temperature.
    But real world objects have a property called emissivity that is the
    ratio of how they radiate when compared to the ideal black body.
    Blackened steel glows much brighter (has a higher emissivity) than
    highly polished silver so reading the color of a piece of heated
    steel is much easier than the brightly polished silver just because
    there is more light given off. If you take your hypothetical steel,
    copper and glass and heat to the same temperature your eye will read
    the as slightly different colors in part due to the shear difference
    in brilliance of the radiated light. Also there is a variation in
    the radiated spectra for different elements (the basis of optical
    spectrography ) so there is actually a minor color difference at the
    same temperature for different elements. So the colors are a good
    rough rule of thumb but not as useful as a pyrometer :-) 

Jim

James Binnion
jbin AT mokume-gane.com
James Binnion Metal Arts
http://www.mokume-gane.com
360-756-6550
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