In planetary astronomy often the "color" of an object is described by relative amount of reflected light in the blue versus the red part of the spectrum. If something reflects light equally at all wavelengths it is "grey", if it reflects more light at red wavelengths then it is redder than a grey object, and if it reflects more light at blue wavelengths it is bluer. We often see surfaces change color. A common term used is reddening. This is also used for light from space which appears redder than expected because dust preferentially absorbs blue light.

My students and colleagues have started to use "blueing" or "bluening" in papers to refer to a color change that causes more reflected light in the blue (or less in the red). This really bothers me as it is not a real word to my knowledge and sounds awkward. I keep changing things to "becoming less reddened" - but that becomes awkward after awhile.

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    I definitely would go with blueing and not "bluening". But if you don't want to use either, then I'd suggest "Becoming more blue" instead of "becoming less reddened"
    – Jim
    Commented Jan 5, 2015 at 6:15
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    "Reddening" and most related words seem to have come the metaphorical way rather than directly from their literal sense; that is, the use was first in a metaphorical sense. This explains why there are such word forms for some colors but not for others. Thus, it may not gel with the flow of the writing to say blueing or bluening as much as reddening or blackening can. If, say, in a chemical process something typically turns to blue, then contextually, blueing could be an expression of the phonomenon, but the same cannot be used outside (in general English writing). Just my thoughts.
    – Kris
    Commented Jan 5, 2015 at 8:06
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    For the record, the reason bluening sounds so bizarre is that the factitive/causative suffix -en (which is only semi-productive in current English anyway) is highly restricted: it can only be applied to simple, monosyllabic roots that end in an obstruent (including fricatives, but excluding nasals). That's why there's a redden/blacken/whiten, but no *greenen/orangen/bluen/purplen/yellowen, etc.: they are either polysyllabic or they end in non-obstruents (including vowels and nasals). Commented Jan 5, 2015 at 14:18
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    However, if we're talking about technical terms referring to spectral movement, one could easily form the causative emblue, using the prefix form that shows up in enjoy, embitter, enlighten. This would naturally encode the linear difference of the two ends of the visible spectrum. Commented Jan 5, 2015 at 14:42
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    @tchrist: I'm not sure that's enough to say the spelling must be "bluing" - after all, that means about 25% of uses in published books (that ngrams includes) do go for "blueing". To put that in perspective, in the same year, "color" outnumbers "colour" by an even greater ratio; is "colour" a horrific mis-spelling too?
    – psmears
    Commented Jan 6, 2015 at 8:57

10 Answers 10


To blue ( from TFD)

  • (tr. & intr.v. blued, bluing, blues) To make or become blue.

Ngram blued, bluing.

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    The word bluing is also a well established term in metalworking, so it is absolutely appropriate to use it for other circumstances where there is a change in colour. Karen's colleagues might like to use the established spelling to avoid looking silly. Commented Jan 5, 2015 at 9:49
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    And general reference. Commented Jan 5, 2015 at 10:21
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    "I'm afraid I just blue myself"
    – prawn
    Commented Jan 5, 2015 at 15:48
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    And next up is the Elvis track, "To Leave Me Will Be To Blue My Christmas". (In this reality Elvis never made it very far...)
    – BrianH
    Commented Jan 5, 2015 at 20:23
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    It's also a well-established process in laundry and hair-rinsing.
    – bye
    Commented Jan 6, 2015 at 5:10

As English already has terms like reddening, yellowing, greening, greying, whitening, blackening, browning, purpling, silvering and goldening to describe a change in colour, it's hard to see what you find so objectionable about blueing.

Your colleagues clearly feel that it is a necessary addition to the lexicon of their profession, and are consequently employing it in their papers; so on what basis do you claim that "it is not a real word", besides the fact that you have convinced yourself that this is (or ought to be) the case?

Words are coined in response to a felt need; language is a tool to be used for the purpose of communicating meaning. Your colleagues are using it in exactly that way.

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    goldening? never heard that one...
    – Tim
    Commented Jan 5, 2015 at 13:33
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    This is a good comparison, but I'd suggest going with spelling it bluing instead of blueing. Dropping the ending e is pretty standard here, and it avoids three vowels in a row.
    – Bobson
    Commented Jan 5, 2015 at 19:54
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    @Bobson: And the fact that the word with that spelling already exists; one does not need to resort to arguments that a word is needed to justify it.
    – Ben Voigt
    Commented Jan 5, 2015 at 20:36
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    Blueing [sic] is objectionable because it’s misspelled.
    – tchrist
    Commented Jan 5, 2015 at 21:57
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    @Bobson Are you sure you want to avoid consecutive vowels? xkcd.com/853 Commented Jan 6, 2015 at 20:28

In astronomy or photochemistry, "blueshifting" is the word you're looking for when describing the opposite to redshifting. Personally I've never heard people even in scientific circles say "blueing" or "bluing".

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    However, blueshifting and redshifting refer to the change of colour due to Doppler's effect, while here, I believe the change of colour is related to the star's inner properties. These two things certainly should be distinguished.
    – yo'
    Commented Jan 5, 2015 at 10:40
  • @yo': en.wikipedia.org/wiki/Blueshift implies that "blueshift" is used not only for the Doppler effect.
    – user21820
    Commented Jan 5, 2015 at 10:52
  • However, I believe that the colour change discussed here is of chemical origin, not gravitational one, i.e., not cause by a change of the photon's energy, but rather by different spectrum being ejected in the first place. However, that's something for the OP to know, I just point out that the phenomenon they study is not necessarily a shift and these notions need not apply.
    – yo'
    Commented Jan 5, 2015 at 10:59
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    Even if it's not just Doppler shift blue shift to a physicist (and presumably an astronomer) implies a moving of features within a spectrum. The question is talking about a filtering or removal of part of a spectrum - quite likely a continuous spectrum.
    – Chris H
    Commented Jan 5, 2015 at 17:48
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    @user21820 when it comes to reflection off astronomical objects it would seem fair to assume that we only need to consider elastic scattering with a wavelength-dependent efficiency. We can also consider that the OP wants an antonym to reddening, not redshifting.
    – Chris H
    Commented Jan 6, 2015 at 9:19

To blue is already a perfectly cromulent English word, which is to say, it's found in large dictionaries but not used by normal people.

I would tend to prefer the made-up word bluening over bluing in this technical context: 20% for symmetry with reddening, 40% because the verb bluing already has a completely different technical meaning (it refers to a metalworking process), and 40% because using the word blue or blues will most likely render your sentences hard to understand. "Stars in the above class blue over time" is parseable, but IMHO awfully close to "The horse raced past the barn fell".

If you absolutely must have a "simple English" answer, what's wrong with becoming bluer? I don't understand why you'd have jumped all the way to the circumlocutory becoming less reddened when you could just say becoming bluer or becoming more blue.

Also notice that reddened is the adjective that you get when you take the adjective red, verb it, and then adjectivize it again. As such, it's pretty much just a complicated synonym for red; so you could have jumped only slightly less far, to becoming less red.

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    Bluening sounds very weird to my ear, but it's not actually any stranger than whitening or blackening. I guess it's just the lack of bluen as a common adjective - I've heard it, but not very often.
    – Bobson
    Commented Jan 5, 2015 at 21:05
  • The next time I read an answer that says such and such a word is cromulent I will downvote it for lacking originality.
    – Mari-Lou A
    Commented Jan 7, 2015 at 6:06

When referring to color, it is common to use the terms warm/warmer and cool/cooler. If the context would not be confused by using words that ordinarily refer to temperature, this would express a range of colors more accurately.

"The red hue cooled to near violet, before warming up again to a vibrant crimson."

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    Best not to go there in astronomy, though, where red is a cooler colour and blue is a hotter one. Commented Jan 5, 2015 at 14:01
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    How weird is that, right? I wonder why? Does the light spectrum react in the opposite direction when it reflects extreme heat? Or, start over in the middle, like, ROYGBIVIBGYOR? (Any physicists out there?)
    – Oldbag
    Commented Jan 5, 2015 at 16:03
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    I think it's just that hot things humans experience (like fire and heated metal) are red/orange because they're just not hot enough to be blue/white. Whereas cold things we experience (like snow and bodies of water) are white and blue, but not because of their temperature. Whereas astronomers don't care about things humans experience, they care about the colours of stars and the fact that blue light is higher energy than red light. Commented Jan 5, 2015 at 16:17
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    @SteveJessop - Actually, the core of a candle flame is generally blue, but most people don't look closely enough to notice it (or at least don't think of it when they're talking about flame color).
    – Bobson
    Commented Jan 5, 2015 at 21:03
  • @Bobson not only that but how many people stop to consider where the hottest part of the flame is? The blackbody emission from the soot in the yellow parts of the flame is also much brighter.
    – Chris H
    Commented Jan 6, 2015 at 9:21

There isn't an equivalent of reddening for the color blue. I will add in my vote that using blue in the same sense as redden sounds jarring and distracting. Blue could be used this way but it still sounds "odd" - bluing conjures up images of a chemical process in my mind.

Use the term turning blue - it has the same number of syllables as blue-ening if that was a word - or turning bluish/turning towards blue if one of those would work better.

You then probably want to avoid the term redden and use the corresponding term turning red/turning reddish/turning towards red.


Bluing/blueing is definitely a legitimate word, though may not be commonly used for the situation you describe.

This term (US Eng: "bluing"; UK/commonwealth often "blueing") is also used in the firearms and steelwork worlds, as a reaction (the formation of surface magnetite), a substance to emulate that reaction (various chemical compounds, typically based around selenium dioxide), and as the verb to describe the process of applying such a substance or reaction to steel, and to describe the color change as the effect takes place.

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    Firearm bluing was my first thought when I read the question.
    – TecBrat
    Commented Jan 7, 2015 at 15:06

Bluing is also a term used for a household product, the purpose of which is literally to give fabric a blue shade (thus the name) to make it appear to have a cleaner white color. My opinion is that if bluing was named after turning something blue, then turning something blue is bluing it.

On a side note, bluing laundry isn't as common as it used to be. The only reason I knew about it is because a poster from Sendak's In the Night Kitchen hangs on a wall in my parents' house:

In the Night Kitchen

See the description on the bottle of Chase-O (Washes and Blues).

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    Bluing, in a broad sense, is actually still a common part of many laundry detergents. It's just made with fancier chemicals nowadays, and called "optical brightener". Commented Jan 7, 2015 at 18:49

I'm aware of the term "cyanosing" being used in medical/paramedic terminology to describe a patient's skin turning blue due to a lack of oxygen e.g. "The patient was unconcious and cyanosing". Cyan = blue.

Also - in Australia "blueing" is colloquial for "fighting" e.g. "The two men were blueing about who was next in line at the bar".


This question became more and more interesting, as I continued researching. Why wouldn't you use the term "Planckian locus"? (It's so cool sounding) It would also be more accurate in describing the colors, for instance, a "bluing-red" sounds like purple - but there are no purple (or green) stars. (See: Planckian locus)

If you wanted to save time and ink, you could agree on an abbreviation, say:

"Plus/minus intensity on the PL -or- (PL+) versus (PL-)

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    When the problem is that "changing things to becoming less reddened ... becomes awkward after a while", I'm not sure the solution is to change them to increasing intensity on the Planckian locus instead.
    – user1635
    Commented Jan 5, 2015 at 18:30
  • What, you didn't like my neat little abbreviations?
    – Oldbag
    Commented Jan 5, 2015 at 18:44
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    @Oldbag It's really annoying and hard to read when people coin their own abbreviations like that. It seems to be somewhat common in philosophy but, in my experience, it's not the done thing in the sciences. Commented Jan 5, 2015 at 18:56
  • @DavidRicherby- I guess medicine isn't a science then... (ALS, ED, COPD, ADD, ADHD, MS, HBP, CP, A-Fib, CAT scan, ICU, etc.) Also, I think Einstein would have had a helluva time doing his equations if he had to keep writing out: "The speed of light".
    – Oldbag
    Commented Jan 5, 2015 at 21:15
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    Yeah, I think "it's not the done thing" is an example of wishful thinking. It would be more accurate to say "it shouldn't be the done thing." ;) (...says me, the guy advocating the use of the made-up word "bluen" in my own answer...) Commented Jan 5, 2015 at 21:36

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