| Topic: |
Science > Physics |
| User: |
"MKrojc" |
| Date: |
30 Jan 2006 04:17:09 AM |
| Object: |
Color darker when wet |
I'm looking for some explanation on why all colors, when wet, get
darker. The thing is, that I have never stumbled on an example when
this is not true. So I'd need some help on why and also if there are
exceptions.
If my explanation id poor, then just wet your color T-shirts :)
Thanks a lot.
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| User: "John Christiansen" |
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| Title: Re: Color darker when wet |
30 Jan 2006 05:28:55 AM |
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"MKrojc" <krojc@email.si> skrev i en meddelelse
news:1138616229.190233.42910@o13g2000cwo.googlegroups.com...
I'm looking for some explanation on why all colors, when wet, get
darker. The thing is, that I have never stumbled on an example when
this is not true. So I'd need some help on why and also if there are
exceptions.
If my explanation id poor, then just wet your color T-shirts :)
Thanks a lot.
I haven't done any research on this so I am a little into guessing. When
radiation hits a surface some of it is reflected and some is absorbed. The
more radiation that is absorbed (and thus less reflected) the darker the
surface, a black surface absorbes at least in theory all radiation. Now if a
surface is wet some of the incoming radiation will be used to evaporate the
water and thus less radiation is reflected and the surface seems darker.
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| User: "Andy Resnick" |
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| Title: Re: Color darker when wet |
30 Jan 2006 07:51:04 AM |
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MKrojc wrote:
I'm looking for some explanation on why all colors, when wet, get
darker. The thing is, that I have never stumbled on an example when
this is not true. So I'd need some help on why and also if there are
exceptions.
Interesting question. It's not *always* true, as getting a metallic
reflecting surface wet deosn't change the percieved color, or intensity.
Presumably you are referring to colors printed on paper, cotton fabric,
etc., where water is absorbed into the matrix. I think the main change
there is a decrease in *scattering* of the incident light. And I
suspect that the hue of the color is firly unchanged (or is it the
saturation?)... instead, the total amount of light that is scattered out
of the paper/fabric is decreased, and so the absoprtive properties of
the dye are less pronounced.
What would be interesting is to try an experiment using fluorescent
dyes, because those directly emit. I bet you would see no changes.
Just a semi-educated guess....
--
Andrew Resnick, Ph.D.
Department of Physiology and Biophysics
Case Western Reserve University
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| User: "MKrojc" |
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| Title: Re: Color darker when wet |
30 Jan 2006 09:06:57 AM |
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Yes, I'm talking about all materials that absorb water!
I did a "test" with cloth, paper and a piece of a brick and I placed
drops of different liquids on it: hexane, kitchen oil, ethanol, water,
glycerol and gasoline. In all cases one drop of liquid changed the
apearence of a "wet" dot color to exactly the same (keep in mind that
my eye was a meter" shade of color even in cases when liquid itself is
not transparent.
But there is a difference, that can be observed only on non translucent
materials - brick in my case. If I take a piece of paper and wet it
then it appears darker only if background is solid, if I look at the
light it appears lighter.
How can I understand this?
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| User: "Hexenmeister" |
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| Title: Re: Color darker when wet |
30 Jan 2006 10:53:56 AM |
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"MKrojc" <krojc@email.si> wrote in message
news:1138633617.754028.120720@z14g2000cwz.googlegroups.com...
Yes, I'm talking about all materials that absorb water!
I did a "test" with cloth, paper and a piece of a brick and I placed
drops of different liquids on it: hexane, kitchen oil, ethanol, water,
glycerol and gasoline. In all cases one drop of liquid changed the
apearence of a "wet" dot color to exactly the same (keep in mind that
my eye was a meter" shade of color even in cases when liquid itself is
not transparent.
But there is a difference, that can be observed only on non translucent
materials - brick in my case. If I take a piece of paper and wet it
then it appears darker only if background is solid, if I look at the
light it appears lighter.
How can I understand this?
Get a photographer's photometer, a light bulb, a darkroom, an ammeter
and start experimenting.
http://www.asdi.com/products-LSP.asp
http://search.globalspec.com/productfinder/findproducts?query=photometer&se=ggka&setag=MFGN
Write a paper and tell us the results.
Androcles.
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| User: "Gregory L. Hansen" |
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| Title: Re: Color darker when wet |
30 Jan 2006 11:47:58 AM |
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In article <1138633617.754028.120720@z14g2000cwz.googlegroups.com>,
MKrojc <krojc@email.si> wrote:
Yes, I'm talking about all materials that absorb water!
I did a "test" with cloth, paper and a piece of a brick and I placed
drops of different liquids on it: hexane, kitchen oil, ethanol, water,
glycerol and gasoline. In all cases one drop of liquid changed the
apearence of a "wet" dot color to exactly the same (keep in mind that
my eye was a meter" shade of color even in cases when liquid itself is
not transparent.
But there is a difference, that can be observed only on non translucent
materials - brick in my case. If I take a piece of paper and wet it
then it appears darker only if background is solid, if I look at the
light it appears lighter.
How can I understand this?
Nice question. I don't know the answer. But what changes when it's wet
versus dry? It's not the chemistry-- wet sidewalks are darker than dry
sidewalks. I can only think of the index of refraction of the liquid,
which is higher than that of air. Maybe in another round of experiments
you can try wetting spots with liquids of different indices of refraction
and see if you can see which is darker.
Also consider that powder is usually whiter than the material it came
from, and polished stones look darker and wet. If you think of polished
granite, like on the side of a building, it looks like granite unless
you're at the angle that the Sun reflects from it. Then it's blinding.
Rough stone reflects light more diffusively, and maybe looks whiter
because the colors of the stone compete with the diffuse reflections from
little tiny mirror-like surfaces pointing in every direction. And maybe
water has a kind of lensing effect that reduces diffuse scattering.
--
"Voice or no voice, the people can always be brought to the bidding of
the leaders. This is easy. All you have to do is to tell them they
are being attacked, and denounce the pacifists for lack of patriotism
and exposing the country to danger." -- Hermann Goering
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| User: "platopes" |
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| Title: Re: Color darker when wet |
30 Jan 2006 09:20:01 AM |
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MKrojc wrote:
Yes, I'm talking about all materials that absorb water!
I did a "test" with cloth, paper and a piece of a brick and I placed
drops of different liquids on it: hexane, kitchen oil, ethanol, water,
glycerol and gasoline. In all cases one drop of liquid changed the
apearence of a "wet" dot color to exactly the same (keep in mind that
my eye was a meter" shade of color even in cases when liquid itself is
not transparent.
But there is a difference, that can be observed only on non translucent
materials - brick in my case. If I take a piece of paper and wet it
then it appears darker only if background is solid, if I look at the
light it appears lighter.
How can I understand this?
Well, you're just seeing through it, aren't you?
p
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| User: "MKrojc" |
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| Title: Re: Color darker when wet |
30 Jan 2006 10:52:43 AM |
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2 platopes a good remark :)
If I see through wet tissue if background is light, it means that I see
through water and not through tissue, and in case of dark background
(or more layers) I see deeper (darker or less illuminated) parts or in
case of a wet T shirt - skin.
How can I then explain if my background is mirror and same thing
happenes?
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| User: "platopes" |
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| Title: Re: Color darker when wet |
30 Jan 2006 07:12:54 PM |
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MKrojc wrote:
2 platopes a good remark :)
If I see through wet tissue if background is light, it means that I see
through water and not through tissue,
Both water and tissue, I'd think. This is a good time to note that
I'm a layman with no formal training/knowledge...nothing.
and in case of dark background
(or more layers) I see deeper (darker or less illuminated) parts or in
case of a wet T shirt - skin.
If adding water to the tissue makes it more transparent, you'll
(better) see whatever is behind it - my guess.
How can I then explain if my background is mirror and same thing
happenes?
Again, depends on how much light is being reflected by the mirror?
Not exactly sure what you mean by "same thing", though.
Note: varnish continues to add "depth" to an oil painting long after
drying.
p
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| User: "MKrojc" |
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| Title: Re: Color darker when wet |
31 Jan 2006 03:36:51 AM |
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I have means to do the "experiment" with a photographer's photometer, a
light bulb, a darkroom and will do it in next days.
Unfortunately I dont have access to Applied Optics, but I found this:
http://graphics.stanford.edu/~henrik/papers/egwr99/egwr99.pdf
It has some useful info.
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| User: "Hexenmeister" |
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| Title: Re: Color darker when wet |
31 Jan 2006 10:42:34 AM |
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"MKrojc" <krojc@email.si> wrote in message
news:1138700211.119777.294940@z14g2000cwz.googlegroups.com...
I have means to do the "experiment" with a photographer's photometer, a
light bulb, a darkroom and will do it in next days.
Unfortunately I dont have access to Applied Optics, but I found this:
http://graphics.stanford.edu/~henrik/papers/egwr99/egwr99.pdf
It has some useful info.
Good luck to you then.
Androcles.
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| User: "Timo Nieminen" |
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| Title: Re: Color darker when wet |
30 Jan 2006 01:13:09 PM |
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On Mon, 30 Jan 2006, MKrojc wrote:
I'm looking for some explanation on why all colors, when wet, get
darker. The thing is, that I have never stumbled on an example when
this is not true. So I'd need some help on why and also if there are
exceptions.
If my explanation id poor, then just wet your color T-shirts :)
If you have access, try:
Lekner, John; Dorf, Michael C.
Why some things are darker when wet
Applied Optics, Volume 27, Issue 7, April 1, 1988, pp.1278-1280
--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/Nieminen,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html
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