Matt wrote:
"Before mentioning the stages that led to the development of photography,
there is one amazing, quite uncanny prediction made by a man called de la
Roche (1729-1774) in a work called Giphantie. "
I don't think what he describes is itself fantasy. There are photosensitive
systems based upon cross linking of the emulsion, such as gell/dichromate. If
you take a photographic plate and remove the silver halide with fixer, then
soak it in potassium dichroate you have a (very slow) photosensitive medium.
Exposure to light causes the protein chains in the emulsion to become cross
linked and relatively insoluble. Subsequent washing removes the remaining
emulsion. This has been used to make phase holograms, the diffraction patterns
being the variation in thickness of the remaining emulsion layer. That's the
modern version.
It has been suggested that a similar process could have been available in the
renaissance period ( when many artists where using the "camera" ie a box with a
lens). The emulsion could be any rendered down animal protein, the oxidising
agent being provided by urine. Ideally UV light is needed for exposure, but
this could be acheived by using a quartz, rather than glass lens.
It is postulated that this may be a process which could have been used to
create the Turin shroud.
Chris Barrett
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