Talk:Transparency and translucency

A portion of a photon?
This following statement referring to one of the possible interactions between a photon and an electron doesn't seem correct:

"An electron selectively absorbs a portion of the photon, and the remaining frequencies are transmitted in the form of spectral color."

Wouldn't an individual photon only be of a distinct single frequency and so there wouldn't be "remaining frequencies" that are transmitted? PizzaAddict (talk) — Preceding undated comment added 04:12, 17 July 2014 (UTC)

Untitled
This article is not helpful, it doesn't give a simple and clear definition of transparency, before getting into further details. —Preceding unsigned comment added by 189.128.91.142 (talk) 19:40, 1 February 2011 (UTC)

Fork
My initial reaction to this article was that it had all the hallmarks of a student essay rather than a Wikipedia article: long introduction on the nature of light which patently duplicates existing articles, limited outgoing links, absolutely no incoming links created, spurious capitalisation.

Logger9, please go and thoroughly read existing articles in this subject area. Ask yourself: would my stuff go better in existing articles. Obviously you replace the introduction with wikilinks. If people other than you agree that the article does not duplicate existing material, then I will accept it. — RHaworth (Talk | contribs) 03:01, 21 January 2009 (UTC)
 * I've worked with logger9 (rather, tried to help him out) via email before, on articles like Colloid Crystal. While he seems to be adapting an essay that he has done for his work; it seems like it could be taken in an interesting direction.
 * In this case, I think you are right though. Logger9, you might be better off writing your material in a section of the Transparency (optics) article, just because it would fit better there. NuclearWarfare  ( Talk ) 03:40, 21 January 2009 (UTC)

Dear Sirs:

I believe this all to be very constructive input :-)

When it was suggested to me (indirectly) last night that I redirect my efforts to the page on Transparency (optics), that is exactly what I did. I immediately transferred over the portion of the article which I believed would fit there appropriately. And I have spent most of today expanding on that subject matter.

But I also feel that the material specific to glasses and ceramics most definitely merits its own page. Nowhere on your published pages do I see a clear distinction between the mechanisms of scattering, absorption and attenuation in the UV-Vis portions and the IR portions of the electromagnetic spectrum. (*Note to recent editor: 'Vis' is short for "visible", not "visual" lightwaves).

Within the context of the recent advances and developments in the field of Materials Science and Engineering, these are specialty topics that I have spent years in both educational and professional circles becoming familiar with. In fact, you would be very hard pressed to find these subjects reviewed adequately in any refereed academic journal. At the same time, the field is currently exploding with global research and development in this subject area.

I would suggest including the material on glasses and ceramics on its own page. In fact, you can see that I have already begun that process under the title of "Transparent Ceramics" -- although I would prefer to keep it under "Transparent Materials" in order to include the optical properties of both ordered (ceramic) and disordered (glassy) microstructures.

I sincerely hope this helps to explain my objectives. I am also quite pleased that the outcome (regardless) is clearly a significant contribution to our presentation of Transparency (optical), as has been expressed already by Mr. Bell.

As far as this being a student essay, it may help for me to note that I am an Associate Professor of Mathematics and Chemistry at a four-year university, and spent several years in the industry working with the processing of optical glasses and ceramics using sol-gel technology.

logger9 (talk) 04:23, 21 January 2009 (UTC)
 * My apologies! I withdraw the "student" bit unreservedly. The "essay" bit hoever is still totally relevant: it looks as though it has been written as a stand-alone dissertation rather than being integrated into an encyclopedia. Why do we need a description of light? We already have articles on electromagnetic radiation and light. Why do we need a discussion of scattering? We already have articles on reflection (physics) and diffuse reflection? &mdash; RHaworth (Talk | contribs) 07:57, 21 January 2009 (UTC)

I guess I just don't understand why there is such a problem with briefly reviewing (and linking) core ideas as they apply within the context of the primary subject matter. I teach chemisty for a living, and I find that the only way people are truly going to learn it is to hear it repeatedly with varied presentations.

I got thru graduate school in Materials Science and Engineering without ever really understanding the nature of the electromagetic spectrum. It wasn't until I was thrown into a fiber optic design group that I was forced to learn it -- and even then it wasn't easy.

In this particular field, it is absolutely essential. I see nothing wrong with a brief reveiw of the subject. In fact, I think that it strengthens the article considerably. I want folks to have a clear distinction in their minds between the UV-Vis and the IR portions of the spectrum of light. And I want them to understand that is all called "light" (not just the visible portion). I don't see that in your articles.

Re: Diffuse reflection. My main points are: 1) It is what we commonly call "light scattering". 2) It is our most typical method of visualizing objects.

Neither of those things are mentioned in the Wiki article you refer to. And why is there no mention of diffuse scattering on your main page on light scattering ???

I.E. A brief review of these subjects is my way of making sure that the article is coherent. This is relatively difficult subject matter to the average reader. I believe that removing them will make it less readable to our audience. I prefer to assume very little about what they already know. That approach to teaching has paid off for me in the regular classroom.

logger9 (talk) 04:15, 22 January 2009 (UTC)

Questions:

1) Why do we need a description of light?

2) Why do we need a discussion of scattering?

Answers:

I believe in briefly reviewing (and linking) core ideas as they apply within the context of the primary subject matter. I teach chemisty for a living, and I find that the only way people are truly going to learn it is to hear it repeatedly with varied presentations.

I got thru graduate school in Materials Science and Engineering without ever really understanding the nature of the electromagetic spectrum. It wasn't until I was thrown into a fiber optic design group that I was forced to learn it -- and even then it wasn't easy.

In this particular field, it is absolutely essential. I see nothing wrong with a brief reveiw of the subject. In fact, I think that it strengthens the article considerably. I want folks to have a clear distinction in their minds between the UV-Vis and the IR portions of the spectrum of light. I also wish to make it clear that all radiant energy is a form of light -- NOT just the visible portion.

Re: Diffuse reflection. My main points are:

1) It is what we commonly call "light scattering".

2) It is our most typical method of visualizing objects.

Neither of those things are mentioned in the Wiki article on scattering. Also, there no mention of diffuse scattering on that page.

A brief review of these subjects is my way of making sure that the article is coherent. This is relatively difficult subject matter to the average reader. I believe that removing them will make it less readable to our audience. I prefer to assume very little about what they already know. That approach to teaching has paid off for me in the both regular and Online classrooms.

logger9 (talk) 04:15, 22 January 2009 (UTC)

Transparency (optics) merger
Logger, can you explain why we have one good article: Transparent materials, and one poor article: Transparency (optics)? The transparent materials article covers optical transparency in great detail, and even references transparency directly in the opening sentence. The existence of two articles which seem to have once been one is baffling and appears to have degraded quality considerably. I am sorry for being harsh in my judgement of quality, but to me this is clearly the case. Cheers —fudoreaper (talk) 07:37, 23 May 2009 (UTC)


 * I have tried repeatedly since January of this year to make it clear to all that a successful merger of the Transparency (optics) article would be quite simple, and that furthermore, the presence of that article would no longer be necessary. But somehow, even though the merger was successful, User_talk:Closedmouth insisted that, even though 1) the information is now redundant and 2) the references may confuse certain readers, the article stay exactly where it is in its unaltered state. I could not seem to convince him/her otherwise. You may want to take it up with that Wike User. I gave it up ! -- logger9 (talk) 02:06, 6 June 2009 (UTC)


 * Thanks for the reply, logger9. It looks like you have put a lot of work into this page, and not much work has been put into the Transparency (optics) page. It has no references, and is very short. I hope you can continue to contribute, but it sure seems like this merger should happen without delay, but maybe that discussion should happen on the optics talk page.  —fudoreaper (talk) 20:22, 8 June 2009 (UTC)


 * Again, the merger is virtually done. The only remaining issue is that the Transparency (optics) article was never removed! -- logger9 (talk) 04:39, 10 June 2009 (UTC)


 * Oh i see! Somehow I missed the idea that you are now only attempting to delete the Transparency (optics) article, or basically, convert it to a redirect to transparent materials. This seems quite reasonable, and the best thing to do for Wikipedia. I have put notices to this effect on the talk pages of both articles at this point.  If there are no objections, I will change Transparency (optics) into a redirect page in a few days. Again, thanks for all your work and your patience, Logger9.  Cheers —fudoreaper (talk) 23:53, 10 June 2009 (UTC)


 * No objections here. I already tried it ! --logger9 (talk) 06:45, 25 June 2009 (UTC)

Paper, T-Shirts and Frosted Glass
Will this article have anything that will explain why paper becomes transparent when it's oiled, or why you can see through wet T-shirts? Oh, frosted glass also becomes transparent when oiled. Alphapeta (talk) 04:55, 21 July 2009 (UTC)


 * You can't actually see through the wet fabric of a T-shirt. You just see the detailed outline of the person's skin underneath it. -- logger9 (talk) 19:52, 31 July 2009 (UTC)
 * Another explanation is in the article, and I'll add a bit on that: much of light attenuation by paper and T-shirt is due to "porous" (non-smooth) internal structure. When you add water or oil, they fill up numerous voids, making material more continuous and thus more transparent. Materialscientist (talk) 00:31, 1 August 2009 (UTC)
 * This is interesting work, MS. You can see what I have added to your comments -- hopefully with your approval :-) -- logger9 (talk) 05:34, 1 August 2009 (UTC)
 * Your reluctance to refer to density fluctuations in materials with "voids" is unjustified. The density of air (as you know) is far less than the density of any solid matter. Thus a diphasic material filled with air pockets (or voids) will have greater density fluctuations -- which may even resemble a step-function. The direct consequence of this will be refractive index fluctuations - or even discontinuities -- and light scattering. -- logger9 (talk) 21:09, 1 August 2009 (UTC)
 * This is all true, no arguing, I just don't think its right to call material with voids as "density fluctuations in a material" - sounds like twisting the words to me, rewording simple notions with "scientific nonsense" (thats how many see our writing on WP). Materialscientist (talk) 23:01, 1 August 2009 (UTC)
 * If it did not contribute to the explanation, then I might agree with them. But simply to say that these "voids are filled" does not explain why the light will be transmittted. Sometimes things require a certain degree scientific jargon. There is nothing wrong with that, and many Wiki articles in physics and chemistry are filled with it ! I would suggest that we give them both degrees of language. That way they can choose how far they wish to pursue it -- and the serious student can get a real education. -- logger9 (talk) 00:37, 2 August 2009 (UTC)
 * True, but I push to avoid that as much as possible. Here primary is change in the shape of the surface, not in the density, i.e. attenuation is rather due to reflection on the surface irregularities, not density irregularities. Materialscientist (talk) 00:55, 2 August 2009 (UTC)
 * I believe that you are confused. Light transmission is limited by attenuation due to internal scattering and absorption. It has little to do with surface phenomenon. (You yourself referred to the internal structure as the limiting factor in the above post).
 * In contrast, reflected light is what gives us color and outline. But the question was, why does the paper become transparent (not shiny).
 * It is also important to note here that the paper does not become transparent -- but rather transluscent. This is likely because the pulp fibers of which the paper consists are not smaller than the wavelength of visible light. -- logger9 (talk) 00:39, 3 August 2009 (UTC)
 * True about the pulp, but not about transmittance. Both "internal" and "external" scattering contribute; while the former is a required condition, the latter is not. This is especially true when particles are comparable or smaller than the wavelength (e.g. nanotubes, other fibers, etc.) - even if their material is nominally transparent, light mostly scatters on them rather than penetrates them. Every case might be individual - for water drops in the rainbow, light penetration is essential, but for the fabric and paper not. Materialscientist (talk) 00:59, 3 August 2009 (UTC)
 * You are skirting the main issue by describing secondary effects. Even the surface scattering is determined by the index of refraction, which is determined by the average density. You may not "prefer" the language -- but it speaks for itself. Density fluctuations on the surface will contribute to your secondary reflections, and these will be minimized by the addition of the oil. -- logger9 (talk) 02:18, 3 August 2009 (UTC)
 * It might sound like wording, but not: consider fine glass powder in air, very homogeneous, but powder, thus scattering. Now immerse it in a liquid with the same refractive index (glycerol, whatever), still in air. It will become more transparent. Nothing changed with respect to density fluctuations (same air, same glass), only surfaces became smoother. You treat air between glass powder particle as part of glass, but this does not seem correct - same as we should not treat air as part of the closes we wear. Gas trapped as bubbles in glass is another matter. It does not change upon interaction (with atmosphere, etc.) and thus might be treated as density fluctuations, though I'm not sure it is (treated so). Materialscientist (talk) 03:12, 3 August 2009 (UTC)
 * The answer to the original question is that the dry materials are diffuse in part because of their surface geometry -- refraction causes them to appear more opaque than they "really" are if they were bulk materials. The behavior you see is "index matching": If you imerse a transparent material with some surface texture in a liquid with the same index of refraction, it disappears because no refraction happens at its surface. Glass does this in paint thinner. —Ben FrantzDale (talk) 14:57, 7 September 2011 (UTC)

Moved from the main article
I moved the following section here because it is clearly disconnected from the article and too specific. Granted, some vibrational properties might be relevant to IR absorption, but their description is inadequate for this popular article.

==Scattering in glasses and liquids== Thermal motion in liquids can be decomposed into elementary longitudinal vibrations (or acoustic phonons) while transverse vibrations (or shear waves) were originally described only in elastic solids exhibiting the highly ordered crystalline state of matter. This is the fundamental reason why simple liquids cannot support a shearing stress, but rather yield via macroscopic plastic deformation (or viscous flow). Thus, the fact that a solid deforms while retaining its rigidity while a liquid yields to macroscopic viscous flow in response to the application of a shearing force is accepted by many as the mechanical distinction between the two.

The inadequacies of this conclusion, however, were pointed out by Frenkel in his revision of the theory of elasticity in liquids. This revision follows directly from the continuous characteristic of the structural transition from the liquid state into the solid one when this transition is not accompanied by crystallization – ergo the supercooled liquid. Thus we see the intimate correlation between transverse acoustic phonons (or shear waves) and the onset of rigidity upon vitrification, as described by Bartenev in his mechanical description of the vitrification process.

The relationship between these transverse waves and the mechanism of vitrification has been described by one author who proposed that the onset of correlations between such phonons results in an orientational ordering or "freezing" of local shear stresses in glass-forming liquids, thus yielding the glass transition. Molecular motion in condensed matter can therefore be represented by a Fourier series whose physical interpretation consists of a superposition of supersonic longitudinal and transverse waves of atomic displacement with varying directions and wavelengths. In monatomic systems, we call these waves: density fluctuations. (In polyatomic systems, they may also include compositional fluctuations.)

The velocities of longitudinal acoustic phonons in condensed matter are directly responsible for the thermal conductivity which levels out temperature differentials between compressed and expanded volume elements. Kittel proposed that the behavior of glasses is interpreted in terms of an approximately constant "mean free path" for lattice phonons, and that the value of the mean free path is of the order of magnitude of the scale of disorder in the molecular structure of a liquid or solid. Klemens subsequently emphasized that heat transport in dielectric solids occurs through elastic vibrations of the lattice, and that this transport is limited by elastic scattering of acoustic phonons by lattice defects (e.g. randomly spaced vacancies). These predictions were confirmed by experiments on commercial glasses and glass ceramics, where mean free paths were apparently limited by "internal boundary scattering" to length scales of 10 - 100 micrometers.

The first theoretical study of the light scattering by thermal phonons was done by Mandelstam in 1918 (see Fabelinskii, 1968; Landau, et al.,1984) and published in 1926 (Mandelstam, 1926). Brillouin predicted independently the scattering of light from thermally excited acoustic waves. Gross gave the experimental confirmation of such a prediction in liquids and crystals. With the development of laser technology, the original experiments using the technique of Brillouin scattering on fused silica glass confirmed the existence of structural interfaces and defects on spatial scales of 10 - 100 micrometers. The mechanism of the absorption of sound in solids – which is responsible for the damping of elastic waves of atomic and molecular displacement (or density and compositional fluctuations) – was considered by Akheiser, who regarded the absorption as arising partly from heat flow and partly from viscous damping. In this interpretation, modulated phonons "relax" towards local thermal equilibrium via anharmonic phonon-phonon collisions. This relaxation is an entropy producing process which removes energy from the sound wave driving it, and thus damps it. These conclusions would appear to be consistent with Zener's interpretation of internal friction in crystalline solids being due to intergranular thermal currents.

Improvements in the theory have made it possible to reasonably predict the acoustic loss of non-crystalline solids from the known thermal and elastic properties. Results indicate that infrared optical vibrational modes can contribute to such phenomena. This is not surprising in light of the notion that optic phonons can indeed carry heat in crystalline solids if the acousto-optic energy gap is small enough, and if the optic phonon group velocity is large enough. Mechanisms of attenuation of high-frequency shear modes and longitudinal waves were considered by Mason, et al. at Bell Labs with viscous liquids, polymers and glasses. The subsequent work in the Physics Department of the Catholic University of America led to an entirely new interpretation of the glass transition in viscous liquids in terms of a spectrum of structural relaxation phenomena occurring over a range of length and time scales. Experimentally, the use of light scattering experiments makes possible the study of molecular processes from time intervals as short as 10−11 sec. This is equivalent to extending the available frequency range from 109 Hz or greater than 109 Hz.

According to both Brillouin and Fabelinskii, the scattering is caused by the diffraction of incident planar monochromatic light waves by spontaneous, sinusoidal density fluctuations (i.e. standing thermal sound waves, or acoustic phonons). The light wave is considered to be scattered by the density maximum or amplitude of the acoustic phonon, in the same manner that X-rays are scattered by the crystal planes in a solid. The role of the crystal planes in this process is analogous to the planes of the sound waves or density fluctuations.

Density fluctuations are responsible for the phenomenon of critical opalescence, which arises in the region of a continuous, or second-order, phase transition. The phenomenon is most commonly demonstrated in binary fluid mixtures, such as methanol and cyclohexane. As the critical point is approached the sizes of the gas and liquid region begin to fluctuate over increasingly large length scales. As the length scale of the density fluctuations approaches the wavelength of light, the light is scattered and causes the normally transparent fluid to appear cloudy.

The study of light scattering by thermally driven density fluctuations (or Brillouin scattering) has been utilized successfully for the measurement of structural relaxation and viscoelasticity in liquids, as well as phase separation, vitrification and compressibility in glasses. In addition, the introduction of Dynamic Light Scattering (or Photon Correlation Spectroscopy)has made possible the measurement of the time dependence of spatial correlations in liquids and glasses in the relaxation time gap between 10−6 sec and 10−2  sec in addition to even shorter time scales – or faster relaxation events.

It has therefore become quite clear that light scattering is an extremely useful tool for monitoring the dynamics of structural relaxation in glasses on various temporal and spatial scales and therefore provides an ideal tool for quantifying the capacity of various glass compositions for guided light wave transmission well into the far infrared portions of EM spectrum.

"Diffuse Reflection"
Rough and irregular surfaces cause light rays to be reflected in many random directions. This type of reflection is called “diffuse reflection”, and is typically characterized by wide variety of reflection angles. Most of the objects visible to the naked eye are identified via diffuse reflection. Another term commonly used for this type of reflection is “light scattering”. Light scattering from the surfaces of objects is our primary mechanism of physical observation. This is actually physically inaccurate: While surface roughness does cause a blurring of specular reflections, affecting whether an object appears dull or polished, diffuse reflection is instead caused by light refracting into a material, and being subject to both absorption and scattering within the material (and ultimately a more or less substantial portion being refracted back out), a process known as subsurface scattering or subsurface light transport in 3D computer graphics. This effect is most obvious in wax-like materials, but actually forms the basis of diffuse reflection in virtually all substances. —Preceding unsigned comment added by 81.173.154.196 (talk) 09:03, 15 September 2009 (UTC)
 * How about strongly absorbing (metals, etc.)? Materialscientist (talk) 09:09, 15 September 2009 (UTC)

Regarding "the nature of the light (its wavelength, frequency, energy, etc.)"
Since a given photon has a specific energy, and from that both the wavelength and its reciprocal, freqency can be derived, it is misleading to list these three properties as if they were independant, and to add "et cetera" as if there were more similar properties.

From http://en.wikipedia.org/wiki/Photon:


 * What about the amplitude (or intensity) ??? -- logger9 (talk) 18:25, 18 September 2009 (UTC)

A photon has two possible polarization states and is described by exactly three continuous parameters: the components of its wave vector, which determine its wavelength λ and its direction of propagation.

Also from http://en.wikipedia.org/wiki/Photon:

The energy and momentum of a photon depend only on its frequency (ν) or equivalently, its wavelength (λ):



where k is the wave vector (with the wave number k = 2π/λ as its magnitude), ω = 2πν is the angular frequency, and ħ = h/2π is the reduced Planck constant.[13] —Preceding unsigned comment added by Ted.the.nuke (talk • contribs) 13:32, 16 September 2009 (UTC)

No real explanation
I'm writing as an outsider and non-expert here, but it seems to me that there is no real explanation in this article of why some materials like glass are transparent and other not, other than circular ones, ie that they do not absorb and scatter light. If glass does not scatter light as much as rock, why is that so? If the scattering process is due mainly to pores, would any pore-free material without color centers be translucent? if it is Rayleigh scattering, why don't glass molecules scatter in this manner? —Preceding unsigned comment added by 85.232.197.233 (talk) 11:12, 13 March 2010 (UTC)

Missing reference in "Multi-phonon absorption"
Hi Logger9, nice you reacted so quickly to the tag I left. Unfortunately, the problem is not solved that easily. What I am missing is not "some reference" but "something" (be it an explanation or at least a reference) that explicates the connection between multi-phonon absorption and the subject of this article, transparancy. The Kittel reference is of no help, and phonons should be explained in the "phonon" article, not here, right? -- 84.153.12.215 (talk) 05:48, 8 November 2010 (UTC)

Terminology
Is there terminology to differentiate materials that are transparent but tinted (like a red color gel or blue glass bottle) from materials that are essentially transparent at all visible wavelengths? Obviously it is a matter of degrees, as there is probably no material (short of a vacuum) that has 100% transmission at all wavelengths, but I sometimes get in to conversations like
 * "This is transparent."
 * "No it's not, it's green."
 * "Yes it's green, but it's transparent green."
 * "So it's not transparent, it's green?"

Is terminology for this? I've sometimes tried to impose "clear" being transparent across the visible spectrum, but I don't think that's standard. —Ben FrantzDale (talk) 15:02, 7 September 2011 (UTC)
 * To answer my own question, "colorless" is a useful word for disambiguating this sort of thing. —Ben FrantzDale (talk) 01:29, 14 June 2012 (UTC)

External links modified
Hello fellow Wikipedians,

I have just added archive links to 3 one external links on Transparency and translucency. Please take a moment to review my edit. If necessary, add after the link to keep me from modifying it. Alternatively, you can add to keep me off the page altogether. I made the following changes:
 * Added archive http://web.archive.org/web/20090121035424/http://sol.sci.uop.edu:80/~jfalward/physics17/chapter12/chapter12.html to http://sol.sci.uop.edu/~jfalward/physics17/chapter12/chapter12.html
 * Added archive http://web.archive.org/web/20090122074601/http://www.cem.msu.edu:80/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm to http://www.cem.msu.edu/~reusch/VirtualText/Spectrpy/InfraRed/infrared.htm
 * Added archive http://web.archive.org/web/20090415161723/http://www.harricksci.com:80/infoserver/optical%20materials.cfm to http://www.harricksci.com/infoserver/Optical%20Materials.cfm

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