P3D "alluring, illusive, iridescent color effect"

[John Toeppen <toeppen@xxxxxxxxxxx>]

......."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/


------------------------------

End of PHOTO-3D Digest 2938
***************************