[pure-silver] Re: Pinhole photography using directly scanned photographic paper.
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: "Pure-Silver Free" <pure-silver@xxxxxxxxxxxxx>
- Date: Tue, 13 Jan 2009 12:14:15 -0800
----- Original Message -----
From: "Ken Hart1" <kwhart1@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, January 12, 2009 11:22 AM
Subject: [pure-silver] Re: Pinhole photography using
directly scanned photographic paper.
All I got at the link was a pdf of a title page, no
further details, so I can't speak intelligently. There was
at one time a product called "Printing Out Paper". I don't
know if anyone is still making it or if this is what is
being used. POP was used for contact printing proofs. The
negative was sandwiched with the paper and exposed to an
intense light (sunlight?) for a few minutes. A warmtone
image appearred and lasted for a few months if protected
from intense light. No chemicals were required.
Ken Hart
kwhart1@xxxxxxxxxxx
FWIW, Printing Out Paper (POP) was made until recently
by Kentmere and sold in the USA as Centenial paper and I
think some other brands. POP uses an unwashed emulsion with
an excess of silver. The image appears on direct application
of very intense light, such as sunlight. POP was used for
proofing portraits for decades and was supplied by every
paper manufacturer. I think the last of that was Kodak's POP
which was discontinued about twenty-five years ago.
The image on POP is photolytic silver, that is, metallic
silver which is converted by direct application of light to
the emulsion. Since any exposure to light produces more
silver the image is not permanent unless given additional
treatment. This usually consists of first toning in a toner
which affects the metallic silver but not the halides,
usually a gold-based toner although some other metals are
sometimes used. The second step is fixing out the remaining
halides, usually in a plain fixing bath considerably weaker
than that used for conventional materials. The idea being to
prevent bleaching out of the desired image. The print is
then washed and dried in the usual way. When POP was widely
used there were numerous formulae for toning and combination
fixing and toning baths. In general it separate toning and
fixing steps were considered best practice.
Kentmere appears to have discontinued POP after the
merger with Ilford. The market is probably very small and
POP is more perishable than conventional "developing out"
materials.
Note that POP has very low sensitivity compared to
developing out materials so its use for making a paper
negative directly in a camera would require impractically
long exposures (many hours).
In the "developing out" process the development stage
is an amplifier so that very little light energy is required
to begin an image. POP, OTOH, has no amplification property
so that all the energy needed for the chemical conversion of
the halides into metallic silver must come from the light
producing the image.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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