P3D Re: "alluring, illusive, iridescent color effect"

["Norm in S.F." <normlehf@xxxxxxxxxxx>]

This is the most elegant color process ever, uh, developed.
Rather than the analysis/synthesis that all commercialy successful color
systems use, this one records the wavelength of the incident light.

Too bad there seems no way to make it commercially practical.

Norm Lehfeldt

John Toeppen wrote:
> 
> ......."alluring, illusive, iridescent color effect" sounds like a
> Lippmann integral color photo to me.  I have held one of his origonal
> plates in the correct light.  It was of flowers in a vase on a table.
> The colors in the silver halide film were similar to those of a bug,
> opal, oil on a wet parking lot, bird and butterfly colors, thin film
> optical coatings, or abalone shell.
> 
> The process required that a pool of mercury was in physical contact with
> the emulsion when the exposure is made.  The plate was dye sensitized
> for the desired colors (panchrome - still b&w just red and green
> sensitive) and the film grain was about 2000 lp/mm.  This was an
> unripened gel where the grain was nearly colloidal with a thickness of
> at least 10 microns.
> 
> The waves of light of a given color pass through the gel layer and
> reflect back on themselves forming standing waves.  This is to say that
> a pattern of light and dark interference fringes form little "flecks of
> light" which develop into little stacks of silver mirrors parallel to
> the glass surface.  The spacing between the mirrors in the stack is 1/2
> wave of the incident light, one wave in reflection.  Thus all of the
> little stacks of mirrors each reflecting only the color of light
> corresponding to the color that they were exposed too.
> 
> This process was revived by Yuri Densyk in 1965 when he invented
> reflection holography.  Lippmann/Bragg holograms are what Yuri called
> them.
> Lasers do a really good job of making those flecks of light.  White
> light holograms are exposed using a collimated beam to illuminate a
> holographic plate at about 45 degrees, and the light passing through the
> plate may be reflected off coins sitting on the emmulsion.  The incoming
> and outgoing beams create standing waves which are the recorded by the
> silver halide (or DuPont, PVA, DCG,etc).
> 
> Lippmann's "best work" was producing an array of glass bead lenslets to
> make a camera that took an array of photos.  Viewed by placing the array
> of photos behind the array of lenses an array of viewpoints was visible
> behind each lenslet  --3D!  One big problem was that the images were
> psuedoscopic.  Inversion was not trivial, especially for round lenslets.
> In 1908.   Cylinderical lenslets could be used with strip images, and
> this was done later, Nimslo was a late player in this game.  I think
> that Ed Land must have been involved in the early lenticular work done
> with rotary camera in WW2.
> 
> I would not suggest floating a plate in a mercury easel beneath an
> enlarger because mercury has highly toxic vapors and is assimilated
> through the skin.  The coherence length of natural light requires that
> the mirror is in contact with the gel layer.  Perhaps one could flash
> the gel with silver by formaldahyde soaking the plates prior to
> immerssion in silver nitrate solution. Rinse dry, and expose throuhg the
> glass.  After exposure, a dilute wash in H2SO4 would remove the silver
> prior to development.  Do not fix.  Swell gel with triethanolamine 1:25
> in H20 to color tune.
> 
> you may care to check out:
> http://www.spie.org/
> for more technical data
> and:
> http://www.cam.org/~rioux/holostar/index.html
> for more on sources for materials etc.
> I find that my 1910 Scientific American Cyclopedia of Formulas tells me
> how to prepare my own plates, and how to flash silver.  It also suggests
> some downright dangerous stuff!
> 
> John Toeppen
> http://home.pacbell.net/toeppen/


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