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  1. #1
    holmburgers's Avatar
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    For Friday... Additive System of Color Photography Based on Iridescent Pigments

    Here's a little something to wet your intellectual whistle for the end of the week.

    US Patent 4,242,428 by Chester Davis, Additive System of Color Photography Based on Iridescent Pigments.

    Don't ask me how I came across this, but suffice it to say I found myself reading it, and was quickly intrigued by this interesting process.

    Lemme see if I can describe it in a nutshell...

    Ok, so we're all familiar with "nacreous" pigments, a.k.a. iridescent pigments, pearlescent pigments, etc. These are thin wafers of mica (typically) and coated with a very thin and precise layer of Titanium Dioxide (again, usually). Other compounds can be used, but the basic idea is the same. Light goes through the thin coating and is refracted into an array of colors that change with our angle of view [see here]. You can get pigments which tend more towards a certain color, determined by the thickness of the coating.

    Now, there's something else going on here . A certain amount of light makes it through the thin coating unscathed, then goes through the mica (which is relatively transparent) and is reflected off the inside surface of the thin TiO2 coating, where it's sent back through the mica, to our eye. This secondary internal reflection is necessarily complementary in color to the initial reflection and serves to desaturate the color from these types of pigments. Thus we get the familiar whitish-blue, whitish-red, whitish-green, appearance that is typical of these kind of pigments. They are not intense and deeply saturated... ...yet.

    What the inventor discovered is that by applying a neutral dye to these pigments, the initial reflection from the TiO2 coating is preserved, but the secondary internal reflection is diminished by the absorbing nature of a black dye, thereby eliminating the addition of complementary light and creating an intense and vivid color from the initial reflection alone.

    The real kicker here is that a black or neutral dye can be substituted for, you guessed it, silver halides! The finely divided silver serves as a filter to strengthen the inherent interference-reinforced reflection color of the pigment. Now we have a means to make this intense and vivid color appear in proportion to a light exposure; the necessary requirement for forming a photograph.

    So this process definitely takes a little bit of imagination, but take for granted that applying a black dye or (metallic silver) to these pigments will give an intense vivid color, which happens to be incredibly light fast since it's completely inorganic and based on interference. Also, the amount of silver needed to create an intense color is claimed to be exceptionally low compared to normal b&w imaging, yet the chemicals used are no different.

    Imagine if you will an emulsion of a silver-salt, and within it a dispersion of these iridescent pigments. The coating might have a pearlescent quality, but it would generally be quite white, if not invisible (the author mentions that its refractive index in gelatin makes it dissappear). However, upon exposure and development, vivid colors are formed image-wise as the developed silver takes its effect on the "micaceous" pigments.

    I encourage you to read the patent, and use your noodle to imagine the applications of this, particularly to color photography. The author does mention its parallels to Lippmann photography, though it's not entirely the same. But potentially, you could create a positive color image direct out of a camera, with nothing more than b&w photochemicals. Heck, make it a monobath, shoot it in your 8x10", and we're talking about the ability to pull a completely permanent color photograph out of a tank in less than a couple minutes.

    If you are the big tree, we are the small axe

  2. #2
    holmburgers's Avatar
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    A bit more on this...

    The author experiments with a number of different colored nacreous pigments. The color that "blooms" when the coloring matter is added is dependent on the interference-reinforced reflection color that's present in its normal state. It's amplified by the action of developed silver-halide crystals forming around the pigment.

    A mixture of red, green and blue pigments will synthesize to make white light, since this is an additive system. So I believe that for a color print to be possible, the whole thing would have to be coated on a black substrate.

    To anyone with silver-nitrate in their cabinet, the very initial tests described in the patent would be incredibly easy to duplicate. No emulsion required. All the author does is to add silver-nitrate and a reducing/developing agent in an aqueous solution of the pigments. The color should form immediately, and the silver % is very low. These newly formed "pigments" could actually be used all by themselves, in carbon or gum for instance.

    What's really fascinating about this patent and process is the inability to really imagine what this kind of image might look like, but to be propelled by the belief that it probably looks pretty damn interesting. It just goes to show you that this cat we've been skinning; that is, making images with the interaction of different physical materials, could be skinned a thousand different ways.

    It's easy to believe that every method has been tried, every technique has been devised and every mechanism exploited. Carbon, cyanotype, kallitype, silver... that's it right??

    WRONG! It seems the more you look, the more you realize that there are hundreds of things that we've never seen and never even imagined. Within some of those, we might find a process that makes something truly amazing possible.
    If you are the big tree, we are the small axe

  3. #3
    Mustafa Umut Sarac's Avatar
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    These Mica pigments are widely used in Warmglass or Enamel art.

    Here is an excellent link to list mica colors for warm glass and jewellery applications.

    Very charming colors , looks authentic , patent is great , you can buy mica beads from a wholeseller with little grams and apply that coating and see what its looks like.

    I think they use pink mica in kindergarten girls pens.

    Looks like Barbie ? plastic , fantastic .

    Cool sheen , I like it , looks like Mikimoto Cultered Pearls Catalog Colors .

    Umut
    Last edited by Mustafa Umut Sarac; 07-24-2012 at 01:35 AM. Click to view previous post history.

  4. #4
    Mustafa Umut Sarac's Avatar
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  5. #5
    holmburgers's Avatar
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    Well I have to admit, Barbie Kindergarten Pink Girl's Pens are not exactly what I was hoping for...

    But I do think that a sheeny photograph could be interesting. Truth be told, we don't really know what it might look like!
    If you are the big tree, we are the small axe



 

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