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  1. #31

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    Quote Originally Posted by Struan Gray View Post
    Colloidal silver can be almost any spectral colour. By varying the size and shape of a silver nanoparticle you can adjust the peak of it's reflectance right across the visible spectrum. It's a hot topic in current nanoscience.
    Silver concentration may be another thing to consider. E.g. a dry gelatin layer with colloidal silver may appear red, whereas the same layer, wet, may be yellow.

  2. #32

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    Quote Originally Posted by Ray Rogers View Post
    Considering Struan's field, I would imagine he is aware of Lippmann's work, but perhaps not.

    Martin, who also posts here occassionaly, can fill us in on more about Lippmann Photography, including the current status of a list devoted to it.

    Ron - Don't worry about that little 'moment'... I was about to scream EUREKA! when, while reading Herschel's hand written notes, it became obvious that Herschel had observed and described the beautiful and amazing vivid colors that could be produced by interferance... He wrote:

    " For a remarkable production of color by diffraction see [...]
    This is an most singular phenonomon "

    I was thinking he had beaten Lippmann by decades... that was untill I said to
    myself: "NO! No way people could have missed such an important thing!" It took a few minutes but eventually I saw "diffraction" where once that "interference" had been so crystal clear!

    Hummm...

    OK, well now I am confused myself... again!

    Two works:

    Improvements in the Diffraction Process of Color Photography
    Herbert E. Ives
    (1906)
    -----------------------------------------
    Three-color Interference Pictures
    Herbert E. Ives
    (1907)

    I think Martin could straighten this out...

    Perhaps you are not as old as you think!

    Ray
    There is a forum on Lippmann photography at http://holographyforum.org/phpBB2/vi...e83dbd44457e34

    We tried to put together a collection of classic papers related to Lippmann photography - see:
    www.holowiki.com/index.php/Lippmann_Papers (that site is temporarily down but principally I can send you any of these papers - just give me a PM). Most of these papers are written in French and German (probably for some historic reasons the English speaking world seemed to have ignored Lippmann photography to a large extent).

  3. #33

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    Quote Originally Posted by dwross View Post
    Alright, then. It's decided. If I ever completely lose my mind and decide I need to make colloidal silver myself, it will be with a hand cranked centrifuge!

    Actually...you know...if I set things up right, when we lose power here in the winter for days at a time, I could still make emulsions. Bunsen burner, hand whisk, gaslight. Just kidding (I think).
    There might be easier ways of making colloidal silver. For example, adding a small amount of a reducing agent to a AgNO3/gelatin solution does form colloidal silver. A simple way of doing this is adding ascorbic acid to the above solution. The size of the silver particles depend on different parameters: silver/gelatin/reducer concentration, temperature, time...

  4. #34

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    Quote Originally Posted by Hologram View Post
    Silver concentration may be another thing to consider. E.g. a dry gelatin layer with colloidal silver may appear red, whereas the same layer, wet, may be yellow.
    Yes. I am not sure if it is due to dilution or solvation or both, or hallucination, but I do see color changes as (non-lippmann) emulsions are diluted.

    Struan mentions this when he writes "once the nanoparticles get within a few diameters of each other their optical fields interact and you get a... colour shift...I'm intrigued by the idea that Bensley has made an all-silver image display colours not so much by tuning the size or shape of the silver grains, but by varying the spacing of the silver grains resulting from the second development."

    Perhaps someone could devise a color photographic system based entirely on dilution and or swell?
    Last edited by Ray Rogers; 08-30-2008 at 09:47 AM. Click to view previous post history. Reason: structure

  5. #35
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    In suspensions of fine particles, if you stir them, you often see what appears to be swirls in a moire pattern of colors. This is presumably due to the effect Struan mentions. We see this sometimes in chemical preparations when an ultra fine precipitate is present.

    PE

  6. #36

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    Quote Originally Posted by Ray Rogers View Post
    while reading Herschel's hand written notes[...]

    I was thinking he had beaten Lippmann by decades... that was untill I said to myself: "NO! No way people could have missed such an important thing!"
    Herschel did discover the fixing properties of thiosulfate which went un-noticed for about two decades.

    Sir John Herschel was an amazing person. Although that's not too surprising, considering who his father was, Sir William Herschel who discovered the planet Uranus, and his aunt Caroline Herschel, who devoted her life to assisting John's father in his observations, and rightly discovered several comets on her own.

  7. #37

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    Ray - re google books.

    Are you in Japan? What browser are you using?

    Your browser issue reminds me of when I was in Mexico a few months ago. Google refused to let me see the regular www.google.com and forced me to www.google.mx.

    I really like google books - it's got some pretty interesting stuff there. Especially historical stuff. I can see the entire page, and even download the books that have the links I gave. They have some stuff that have "snippet views" which just annoy me as they obviously have the entire text scanned in but they are trying to avoid copyright infringement by not showing you more than a line or two of the text.

    But there's a lot of interesting stuff there and I suggest you keep trying t find a way to get it to work. I've bought several books that I've seen either the full text or bits of it on google books.

  8. #38

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    Quote Originally Posted by Kirk Keyes View Post
    Herschel did discover the fixing properties of thiosulfate which went un-noticed for about two decades.

    Sir John Herschel was an amazing person. Although that's not too surprising, considering who his father was, Sir William Herschel who discovered the planet Uranus, and his aunt Caroline Herschel, who devoted her life to assisting John's father in his observations, and rightly discovered several comets on her own.
    Yes.

    I tried to follow the hint but the meaning of some code numbers need follow up to confirm exactly what Herschel was referring to... I will have to open up that folder and finish following the lead.

    I agree- He was amazing... I have a lemon soda formula of his I am dying (from the thirst of curiosity) to try!

  9. #39

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    [QUOTE=Kirk Keyes;675191]Ray - re google books.

    Are you in Japan? What browser are you using?

    Your browser issue reminds me of when I was in Mexico a few months ago. Google refused to let me see the regular www.google.com and forced me to www.google.mx.

    They have some stuff that have "snippet views" which just annoy me as they obviously have the entire text scanned in but they are trying to avoid copyright infringement by not showing you more than a line or two of the text.
    QUOTE]

    Yes.

    I guess the same thing is happening to me.
    It seems the site decides to make you use the local (google?) system...
    I can use either google, but the using the link I found only confusing semi related sentences, and honestly, I got so frustrated with- you guessed it those "snippit" strips of torn pages I lost the will to hunt... and have already forgotten what it was exactly.

    Perhaps if I look again I will find a way out, but I am not hopeful.

    I will try again someday, after I recharge.

    Ray

  10. #40
    Struan Gray's Avatar
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    I am sorry for my relative silence: I've been whooping it up in Legoland :-)

    Colour is a big topic, but it is important to realise that there is a fundamental difference between interference colours such as those found in Lippmann emulsions and thin films, and the colours of colloidal silver which are related to excitations of the electrons in the silver particles, and are thus more like the colours of pigments or dyes.

    Interference colours can be very intense and pure, but they generally only work over a limited range of angles. Exceptions exist which work over wider angles - the canonical example is the pure blue of the Morpho butterfly wing - but as I understand it Lippmann emulsions only display their correct colours when viewed head-on.

    I think holographic emulsions are today's direct descendents of Lippmann's work: they perform a similar task of preserving interference fringes in the thickness of the emulsion by laying down correctly spaced lamellea of silver.

    In metallic materials where the electrons are free to move you can create compression waves in the sea of free electrons which are analgous to sound waves in a gas. These are the so-called 'plasmons' which crop up as buzzwords in any modern discussion of the optical properties of small metallic structures. Because the wave changes the local charge density, it has an associated electromagnetic field, and in the right circumstances you can couple that field to the freely propagating plane waves of which light is made.

    It is these plasmon modes which give colloidal silver its colour. Other metals work too: gold for example turns red and then a gorgeous deep blue as you make smaller and smaller particles. Most experiments are done on noble metals because the large surface area to volume ratio of the particles makes them very susceptible to corrosion and oxidation, but in principle aluminium and iron will display similar effects.

    The plasmon frequencies are acutely sensitive to the particle's size, shape and local environment. As I said in my earlier post, nearby particles can radically change the way that a particular particle scatters light, but the properties of the surrounding medium can have a similarly dramatic effect: changes in its refractive index or its pH will often lead to changes in colour.

    This sensitivity is one reason for the widespread interest in applications of plasmonic structures. For example, you can already buy blood sensors where the binding of a protein to a gold film changes the plasmon frequency and alerts a monitoring circuit. It is also the reason that plasmonics seems to promise a tempting wide-tunability across the optical spectrum.

    The problem for photographic applications is that the same sensitivity makes the colour production unreliable, especially with conventional home darkroom levels of control and repeatability. If time, temperature, humidity, and chemical concentations have to be controlled to 0.001% then this isn't a practical photographic technique, even if the same science ends up being used industrially to make sensors or the next generation of LEDs.

    There are of course other mechanisms to make nanostructures more coloured than their bulk analogues. Mie scattering can be highly wavelength and orientation dependent, and the absorbtion that turns large chunks of material grey does not have a chance to work in small systems. Nanowires made from semiconductors show the most beautiful colourations, even in the absence of interference or plasmon effects.

    I should stress that I am not a real plasmonics expert, although I do work with a few, and I have very little relevant experience of the photographic aspects of these phenomena. I very much welcome further discussion, and the valuable practical input from those who have actually got their hands dirty in a real way.

    Final point: the early colour I was thinking of was bare AgCl on a paper support, as used by spectroscopists to investigate projected solar and other spectra by measuring the pyrolitic or photolitic darkening of the halide when exposed to a spectrum from a prism. Herschel reports on some of these colours in his huge catch-all paper in the Royal Society's Phil. Trans. from 1840 (the same paper where he reports the use of "hyposulphites" as a fixer), but I am sure many other early workers noticed and commented upon them. These are unlikely to be caused by an interference effect, and are most likely plasmonic colours.


    Struan
    Last edited by Struan Gray; 09-02-2008 at 04:43 AM. Click to view previous post history.

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