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Is black a colour?

  1. Yes because we can see it physically

    23 vote(s)
    29.9%
  2. Not sure because there are contradicting theories about it

    9 vote(s)
    11.7%
  3. No because it is not within the 7 basic colours of a rainbow that make up white light

    45 vote(s)
    58.4%
  1. Sep 19, 2006 #1
    Hi to all. I will like to propose a question to everyone in this forum. Hope you guys and gals can contribute your opinions and try to derive a conclusion to the following question: Is black a colour?

    I like to announce that this forum is strictly for friendly discussion with regards to the abovementioned topic. Please don't do flaming here. Thanks.

    Well as a start, people may ask me: Why ask this question? So silly and bo liaoz. Actually this question came into my mind just last Sunday. I've applied what I know in science and have the following to present:

    According to the definition of some online encyclopedias, black is defined as an absence of colour. My own definition of black is a phenomenon which totally absorbs all light shining on it, thus rendering it black. Now, is black considered a colour?

    Points raised:

    1) In the electromagnetic spectrum, the human eye can ONLY see the visible light part of the spectrum, that is white light consisting of the 7 basic components - red, orange, yellow, green, blue, indigo and violet. This is familiar for those science students. Since black is not one of the 7 basic colours, black itself is not a colour. On the other hand, it can be argued that the random combination of certain, if not all, colours together can produce black. But does that mean that we mix colours together to produce something not considered a colour, something we cannot see? If black is a colour, it should be within the visible light spectrum but apparently it is not.

    2) Take a black object and a transparent glass for example. In both cases, light from a source does not reflect back to our eye, but for the black object, light is simply absorbed while the transparent glass actually allows light to pass through. However we compare both cases, since both light does not return to us, by right we should see both as identical but instead we see one as black object, another as a transparent glass. Does the future path of the light determine the 'blackness' of an object?
     
  2. jcsd
  3. Sep 19, 2006 #2

    Danger

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    'Colour' is just a term that Anglophones use to describe the various frequencies of electromagnetic radiation. Black is not included. You seem to be using the concepts of 'additive' colour (light) and 'subtractive' colour (pigments) interchangeably, and they're not the same thing.
    This has been discussed quite thoroughly before. Please run a forums search to check out the previous threads. If questions remain, we'll look after them for you.
     
  4. Sep 19, 2006 #3

    arildno

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    Depends on which definition of colour you're using. The scientific definition excludes black, the popular "definition" includes black.

    Much the same as the contrasts between the meaning of the poupular terms "energy, work" vs. the scientifically chosen definitions of the same terms.

    As long as one is clear about which meaning of the term one is using (popular or scientific), there is no need for further discussion of these topics.
     
  5. Sep 20, 2006 #4
    If you can see it, it's a color. A black piece of paper certainly is a color. A black hole is not...
     
  6. Sep 20, 2006 #5

    russ_watters

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    No, it is still just the absence of color. If it absorbs all radiation, then it doesn't reflect any to your eyes and your eyes see nothing.
    You could argue that, but you'd be wrong. The mixture of all colors is white
    No. We see a glass because some light is reflected.
     
  7. Sep 20, 2006 #6

    russ_watters

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    If it were perfectly black, it would send no light whatsoever into your eye and you would therefore not see it.
     
  8. Sep 21, 2006 #7
    Show me any piece of black paper I can't see, with a light shining on it and I'll agree with you...

    I would consider some gasses black (like oxygen), but I don't know of any solid objects that can be considered black by your definition. So it's doubtful that a piece of paper can be perfectly black, If I turn my head black paper doesn't send any light into my eye, does that make it perfectly black suddenly?
     
  9. Sep 21, 2006 #8

    Danger

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    That has so be one of the most specious arguements that I've ever seen on behalf of any cause. No paper is perfectly black. You can never see perfect black. Even if such were right before your eyes, and you had your eyes shut, random photonic events or brain aberations would give specks of light.
    Oxygen, or any other gas, is colourless, not black. Would you describe steam from a teakettle as 'black'?
     
    Last edited: Sep 21, 2006
  10. Sep 21, 2006 #9

    Chronos

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    A thought experiment: A piece of cardboard in a room [let's say the room is painted flat white just for the sake of argument] lit by a single candle placed in the line of sight between myself and the candle flame. Can I 'see' something is there? I would unequivocally say 'yes', would characterize its 'color' as black, and deem it compelling evidence that 'black' is the absence of light.

    An old friend of mine, who was losing his sight due to glaucoma, explained it best:

    "Only two colors exist for me now - black and not-black."
     
    Last edited: Sep 21, 2006
  11. Sep 21, 2006 #10

    In the scientific definition of black you are right, but we as everyday people call things by the color black (a car for instance). Now scientifically you would argue with me that what I call a black car is not black, and you would be right, but I'll continue to refer to it's color as black.

    If something emits or reflects no electromagnetic radiation in the visible spectrum, it is black by definition. Oxygen therefore is black. Colorless and black are the same thing by scientific definition.

    Steam reflects light back to me so no I wouldn't call it black or colorless.

    I know I am presenting two different views here, but I think they both have a proper context.
     
    Last edited: Sep 21, 2006
  12. Sep 21, 2006 #11

    Danger

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    I see your point, but still disagree with it from the scientific viewpoint (and this is a science site, after all).
    To start with, the aforementioned black cardboard is absorbtive of visible EM, but most likely reflects in other wavelengths. For the sake of arguement, I'm accepting that. If you try looking at paint chips or a Pantone chart, though, you'll see that there are an awful lot of different colours deemed 'black'. Obviously, their reflective/absorbtive qualities are different.
    As to my reference to steam, I meant the actual steam rather than the condensed water that you can see. It's invisible. If you take that to mean black, as you suggested, then you could call space black... and it doesn't even exist. How can 'nothing' have a colour quality?
    Chronos, in your example you are not 'seeing' the object. You're seeing the shadow of the object. It could be any colour, and you wouldn't be able to tell (as long as the ambient light is strong enough). All you can know is that there is something blocking the light.
     
    Last edited: Sep 21, 2006
  13. Sep 21, 2006 #12

    russ_watters

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    Jeez, I'm glad you said it before me. Now I don't need to go bang my head against a wall. :grumpy:
     
  14. Sep 21, 2006 #13

    russ_watters

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    You can, of course, believe whatever you want, but this is a science site and from a scientific point of view, the question has an unequivocable right and wrong answer. You are not helping by providing the wrong answer.
     
  15. Sep 21, 2006 #14

    Gokul43201

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    Where did you find this "definition"?
     
  16. Sep 21, 2006 #15

    arildno

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    I would like to say that if we look at our actual PERCEPTION of colours, rather than the physical basis of colours (which is "common man's" way of defining colours), then "blackness" is not perceived as something essentially different than colours proper.

    There is not anything inherently wrong with using actual perceptions as a naive classification scheme for "colours", but it is a scientifically useless definition.

    Other than charting our perceptions, that is..
     
  17. Sep 21, 2006 #16
    It's not a definition, I'm simply relating conditions of matter that fit it into the definition of black. If you have something else to offer I'm all ears.

    If someone here doesn't agree that by definition oxygen, and other colorless gases fit into the definition of black, then I would like an example of something that is black, other than a black hole, which I hope we all agree on.
     
  18. Sep 22, 2006 #17
    Ok I agree with you that for glass, some light is reflected thus we can see the glass. But if we follow the definition that black is absence of colour, then that means no light can reflect back to our eye and we will see nothing, but how come we still can see that 'black' object? Also. If black is a colour, what is its wavelength? If you say it is a colour we can see, then it must have a wavelength between 400nm and 700nm so that it can be part of the visible light of the EM spectrum right?
     
  19. Sep 22, 2006 #18
    Now you guys are arguing two different points, one is talking about color pigments, the other is talking about colored light. Heck their additive theories are completely different, pigments use R Y B for primaries, and light uses R G B for primaries. By definition you are both correct, but there are two definitions. Pigment black is the addition of all the colors together, while light black is simply the the existence of no light at all, or of Electromagnetic light outside of our visible range. As in Infrared light just below our visible red and Ultraviolet just above our visible purple.

    So I'm guessing you are both right, just taking different perspectives since the original question was a little confusing.
     
  20. Sep 22, 2006 #19

    Gokul43201

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    And I'm asking you how you came up with that definition of black?

    A thing is black if it absorbs all the visible radiation incident upon it.

    Why? I can perfectly well define 0 Kelvin, but you won't accept the definition unless I can give you an example of something at 0 Kelvin?
     
  21. Sep 22, 2006 #20

    Why do you keep asking the same question, I already answered it. You want to talk about 0 kelvin, fine. Something that absorbs all visible light obviously doesn't reflect any... Something at 0 kelvin obviously doesn't emit any light... Do you still need to know where I got the definition of black to qualify the above statements? It's irrelivant to the discussion, and just seems more like badgering.

    The issue of wether 0 kelvin exists has been done in many other threads, why start all that again?

    All I'm asking for is a real world example of something black. If you don't know of any fine, just say I don't know.
     
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