From: Phillip Murphy (pmurf@bellsouth.net)
Date: 04/19/03-08:10:04 AM Z
Hello Richard,
There was a discussion recently regarding hypersensitizing
gelatin/silver emulsions. ( I believe that it began with a mistaken
notion that apparent film "speed" could not be increased and
that only contrast index was effected.) Another method for
increasing latent or "sub-image" specks besides gas
hypersensitizing with certain emulsions is a process called
latensification. This process is carried out after exposure
rather than before exposure as in hypersensitization. It is a
very similar system to that of the Becquerel-developed
Daguerreotype. (btw) There is a way of working the Daguerreotype
where you first use Becquerel for a modest amount of time
and then mercury develop the plate. Interesting results can be had
this way. I believe Levi Hill was one of the first to practice the
method.
Anyway, the primary difference for other silver halide systems is that
Becquerel development is generally practiced with a silver-iodide
coating as opposed to a silver-bromide or silver-chloride.
What's needed for those emulsions, (especially panchromatic ones)
is a light source that doesn't create new latent image specks. In the
past, a dark green safelight filter was used with good results. I
would imagine that with the narrow bandwidth of LED's, one could
attempt to find a good film/LED combination that would work for
latensification.
Now, if what you're asking is whether you can creat a silver image
without using a developer, try placing a negative into contact with
any black and white film stock and leave it in room light for a long
while and it will "print-out" by converting halides into photolytic
silver.
I've never known of anyone to do this toward a practical end. I
don't know if it would create enough silver to hold up to "fixing".
Although, it goes without saying that many of the well known
Alt-photo development systems have "printing-out" variations.
"Printing-out" is an entirely different mechanism than
Becquerel-development.
Also, to my knowledge, no one has given an adequate explanation
as to what is occurring when you grow pure silver crystals from a
silver-iodide matrix using long wavelength light.
Nor, what happens when the image is intensified with gold-chloride.
(btw) If anyone out there has any research information on this,
please contact me. Susan Barger has studied the mercury-silver
development of the traditional Daguerreotype and I believe Joe Pollack
has photographed these image particles growing using a SEM. But
it's still a mystery what's occurring there.
all the best,
Phillip
Richard M Koolish wrote:
> Do you know if Becquerel development works with any other
> silver process, like regular film?
>
> > However, I constructed a small LED array using diodes with
> > output in the red region of the spectrum for developing
> > Becquerel developed Daguerreotypes.
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