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The blackbody color spectrum up to about 11,000 degrees Farenheit looks like this:

enter image description here

However, when iron or steel is heated it produces light in the following colors:

enter image description here

So it starts to luminesce at about 1000F and gets white hot at 2500F, not 11,000F. Another difference is that before it reaches white hot, it turns yellow (the image showing green is offcolor, it is actually yellow). However, the blackbody color is more like orange, not yellow.

So, I guess iron cannot be considered a "blackbody", but what is the reason for the difference?

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    $\begingroup$ Can you include a link to your source for these images? $\endgroup$
    – rob ♦
    Commented Aug 31, 2017 at 18:13
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    $\begingroup$ Do you know what a blackbody is? Do you have a reason to expect metals to fulfill the definition of a blackbody? $\endgroup$
    – DanielSank
    Commented Aug 31, 2017 at 18:21
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    $\begingroup$ You should make the two plots have the matching x-axes and color scales to pose a meaningful question. Right now it is not possible to quantitatively answer your question I'd say. $\endgroup$
    – KF Gauss
    Commented Aug 31, 2017 at 18:49

2 Answers 2

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The colors do match. The differences you see are due to the differences in the scale and color index. If you create accurate charts, the colors would be very close. This of course does not include various colors of iron oxides on the surface after it is cooled off.

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  • $\begingroup$ Well, aside from the color issue, the blackbody white is 11,000F and metal turns white hot at 2500F. That is a pretty big difference. $\endgroup$
    – Ambrose Swasey
    Commented Aug 31, 2017 at 19:08
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    $\begingroup$ This is not true. "White" is a perception of the human eye that is evolutionary adjusted to the spectrum of the daylight (the sun plus sky). So white is the color of the black body at the temperature of the sun surface. Iron at 2500F is yelliwish-white like soft light bulbs as opposed to daylight bulbs that have a cooler tint. Again, the discrepancy is only in your data not being precise, but not in the actual phenomena. $\endgroup$
    – safesphere
    Commented Aug 31, 2017 at 19:15
  • $\begingroup$ Because of atmospheric effects, the net sunlight spectrum when it reaches the earth's surface isn't quite a blackbody spectrum anymore. How much it differs depends on location, time of day and weather, but if you imagine a graph where the colour temperature is put on the horizontal axis, going from blue to yellow as you go from left to right, so that the vertical axis goes from pink to cyan, the colour of daylight is typically off from the ideal blackbody colour by about 300 K. (Or equivalently, a blackbody radiator with the same colour temperature... $\endgroup$
    – Anonymous Coward
    Commented Jul 3, 2022 at 16:55
  • $\begingroup$ as daylight is about 300 K too pink compared to what you'd normally consider white.)But that isn't the whole story, because chromatic adaptation is a thing: if the general lighting of a given environment is off-white, but not by too much, you will subconsciously correct for this and after a while the lighting of the environment will appear white to you. This is the reason why, if you normally use your laptop during the day in a naturally lit office, but then look at it after reading for a bit in your ‘flame’-LED-lit living room, the display will appear bluish until you adapt to it again. $\endgroup$
    – Anonymous Coward
    Commented Jul 3, 2022 at 16:55
  • $\begingroup$ @AnonymousCoward Alternatively, we can describe Rayleigh scattering as converting the spectrum to that of a blackbody in $7$-dimensional space. $\endgroup$
    – J.G.
    Commented Jul 4, 2022 at 6:12
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As mentioned by safesphere the perceived white may be misleading as this only tells you something about the relative reaction of the different receptor cells in your eyes.

Besides this I want to add that nearly no object can be considered to be a black body. "black body" denotes an object that has very extreme properties. Black bodies do not reflect or transmit any incident light, regardless of the associated wavelength. Most realistic objects are better described by the term "gray body". These are objects that feature a frequency-dependent light absorption. Of course, this also leads to an emission spectrum that deviates from the idealized black-body radiation. Especially the emission of light at specific wavelengths may be reduced. This can lead to deviating colors in comparison to black-body radiation.

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