P3D Black and White Slides part 2

["Brown, Fritz LABS" <brownf@xxxxxxxxxxxxxxxx>]

Again,  any black and white silver emulsion film can be reverse processed to
produce a black and white transparency.  To do this, one needs to be able to
process black and white film themselves and they need to assemble the
necessary chemistry to do so.  Otherwise, it is no more difficult than
processing black and white negatives.

The chemistry needed to produce black and white films can be purchased in
kit form from Kodak or from the Photographer's Formulary.  Appearantly
Tetnal also sells a reversal kit available in Europe (but I think I remember
a rumor that it has been discontinued so as your darkroom supplier if you
need to know).  The main problem with buying the chemistry in kit form is
the cost.  The last time I priced it locally,  the Kodak kit was going for
about $30 for enough chemistry to process four rolls of film.  Ouch. The
Photographers Formulary kit is cheaper,  but not by a lot.

A note on the kits:  the Kodak kit is based on their own proprietary
chemistry, but the Photographers Formulary kit is based on an article
authored by Hans Deitrich that was published in the March/April 1988 issue
of Darkroom and Creative Camera Techniques (now known as PhotoTechnique).
Get ahold of that article and you will have Deitrich's recipes and
protocols.

So, how does reverse processing work?  Think about the silver emulsion of an
unexposed piece of black and white film.  It has the same amount of silver
halide present everywhere in the emulsion.  When exposed and developed,  but
before fixing,  the sum total of the developed silver and undeveloped silver
is still the same.  For example, if an area of the film received a lot of
light, most of the silver will be developed into metalic silver and a small
amount will remain and silver halide.  In an area that received little light
exposure a small amount of the silver will be reduced to metalic silver and
most of the silver will remain as silver halide.  In an area that received
enough light exposure to expose half of the silver,  half will be reduced to
metalic silver and half will remain as silver halide.  As you can see from
this,  the silver halide is the exact reverse of the metalic silver
immediately after being developed.  Since the metalic silver that we have
developed is a negative,  the silver halide remaining must be the oposite of
that negative and therefore is a positive.

So now that we know that with a piece of black and white film, immediately
after development both the negative and the positive image are present in
the film, how do we go about discarding the negative and retaining the
positive?  Next message.