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Author Topic: Does Glass, Water and A Mirror Have A Colour ?  (Read 7696 times)

Offline neilep

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Does Glass, Water and A Mirror Have A Colour ?
« on: 14/06/2008 21:33:20 »
Dear People Who Enjoy Colours (USA Trasnlation service "Colour" = "Color".....Sheesh !!)


Wood is brown,
Blood is red
I'm feeling Blue
Blue says I'm dead !
......(LOL....stupid sicko ditty for a Saturday night !)

erhhmmm....anwyay...

This could be a very silly question but as I was drinking my glass of water and caught the sparkle of my eyes in the mirror... ::)it occurred to me as to whether there was a designated colour attributed to water,glass and mirrors ?....is there ?

Look for yourself !






What colour would ewe say they are ?



Neil
Escapee from the wrath of the wench named 'Blue '





 

Offline chris

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #1 on: 14/06/2008 21:52:44 »
The "mirror" is a silvered layer behind the glass, so that's silver. The water is colourless and transparent, although it can behave like a mirror (and appear silver) if the angle of incidence is sufficiently shallow - i.e. light hitting the surface at a shallow enough angle is totally internally reflected, making the surface look silvery (this is also how fibre optics work).

Chris
 

Offline rosalind dna

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #2 on: 14/06/2008 23:03:21 »
Chris,
I wear specs and sometimes get the same or similar effect, how does
it work since my irises/eyes are hidden from the specs well sort of.
 

Offline RD

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #3 on: 15/06/2008 03:53:25 »
Reflections from silvering on mirrors, (or polished metal objects), do not reflect all colours equally.
Although the main discoloration with mirrors is due to the green tint of the glass.

The absorption spectrum of water depends on its state...



http://www.lsbu.ac.uk/water/vibrat.html#ir
« Last Edit: 28/06/2008 14:03:22 by RD »
 

Offline Bored chemist

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #4 on: 15/06/2008 10:23:24 »
Some of the earliest mirrors were made of bronze or gold. They were, of course, coloured.
Most glass is pale green due to the presence of impurities, largely iron, in the materials it was made from.
 

lyner

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #5 on: 15/06/2008 15:27:49 »
Most people have some sort of photo processing application on their computer. On Photoshop and others you will find a utility which will show you the RGB values of pixels. Look at a 'white' patch and look at the numbers. If it is 'true' white, it will say 255,255,255 -or, at least, all equal values. You may well see 253, 252, 254 and it will still look white.
What I am trying to say is that white is, nominally, equal or nearly equal subjective amounts of Red, Green and Blue channel signals. The spectrum of Sunlight is not 'flat' but has a broad peak around green. There are very few substances which reflect all wavelengths equally but we are quite tolerant about it and will call many very pale colours (i.e. very desaturated) 'white' until we have a better white to compare them with.
 

Offline LeeE

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #6 on: 15/06/2008 15:48:17 »
AFAIK, in modern fibre optic 'cable' the refractive index varies over the cross-section so that the light pulses get bent back towards the middle, rather than being reflected off the sides.
 

Offline neilep

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #7 on: 15/06/2008 18:40:29 »
Thank Ewe All !

Fascinating reading and great contributions !


So, like the glass and water in my piccy, they are deemed colourless..

Thanks again.....
 

lyner

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #8 on: 15/06/2008 21:24:23 »
AFAIK, in modern fibre optic 'cable' the refractive index varies over the cross-section so that the light pulses get bent back towards the middle, rather than being reflected off the sides.

It's called graded index fibre. Very clever because it reduces the big problem of pulse spreading. Whichever path the light takes, it effectively takes the same time - hence no dispersion - hence a higher pulse rate is possible.

You say they are bent back rather than reflected - it is the same basic principle as it is still total internal reflection (lossless reflection) but is more gradual and the place where the actual reflection takes place depends on the angle of each ray. This also happens with radio waves when they are reflected by the Ionosphere - it is also a distributed effect rather than at a particular surface.
« Last Edit: 15/06/2008 21:29:40 by sophiecentaur »
 

Offline LeeE

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #9 on: 15/06/2008 22:54:40 »
Hmm...  they way it was explained to me, by a bloke in the pub that I used to drink with and who worked on the STL team that largely developed it, it was more a case of refraction rather than reflection.

But then we were in the pub :)
 

Offline DoctorBeaver

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #10 on: 16/06/2008 07:52:29 »
The water is colourless and transparent, although it can behave like a mirror (and appear silver) if the angle of incidence is sufficiently shallow - i.e. light hitting the surface at a shallow enough angle is totally internally reflected, making the surface look silvery (this is also how fibre optics work).

Chris

I have it on good authority that water is blue.

Plus, from Wikipedia...

The color of water is a subject of both scientific study and popular misconception. Pure water has a light blue color which becomes a deeper blue as the thickness of the observed sample increases. The blue color is caused by selective absorption and scattering of the light spectrum. Impurities dissolved or suspended in water may give water different colored appearances.

Or a more geeky explanation from http://www.webexhibits.org/causesofcolor/5B.html

Water owes its intrinsic blueness to selective absorption in the red part of its visible spectrum. The absorbed photons promote transitions to high overtone and combination states of the nuclear motions of the molecule, i.e. to highly excited vibrations. To our knowledge the intrinsic blueness of water is the only example from nature in which color originates from vibrational transitions. Other materials owe their colors to the interaction of visible light with the electrons of the substances. Their colors may originate from resonant interactions between photons and matter such as absorption, emission, and selective reflection or from non-resonant processes such as Rayleigh scattering, interference, diffraction, or refraction, but in each case, the photons interact primarily or exclusively with electrons. The details of the mechanism by which water is vibrationally colored will be discussed in the paragraphs which follow.

Laboratory observation of the vibrational transitions that give water its color requires only simple equipment. The graph at right gives the visible and near IR spectrum of H2O at room temperature. The absorption below 700 nm in wavelength contributes to the color of water. This absorption consists of the short wavelength tail of a band centered at 760 nm and two weaker bands at 660 and 605 nm. The vibrational origin of this visible absorption of H2O is demonstrated by the spectrum of heavy water, D2O. Heavy water is chemically the same as regular (light) water, but with the two hydrogen atoms (as in H2O) replaced with deuterium atoms (deuterium is an isotope of hydrogen with one extra neutron -- the extra neutron that makes heavy water "heavy," about 10% heavier). Heavy water is colorless because all of its corresponding vibrational transitions are shifted to lower energy by the increase in isotope mass. For example the H2O band at 760 nm is shifted to approximately 1000 nm in D2O.


Here is the graph referred to in the above paragraph...

« Last Edit: 16/06/2008 07:57:38 by DoctorBeaver »
 

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Does Glass, Water and A Mirror Have A Colour ?
« Reply #10 on: 16/06/2008 07:52:29 »

 

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