From: Ed Buffaloe (EdBuffaloe@unblinkingeye.com)
Date: 03/09/02-03:37:23 PM Z
When I look over Stevens' and Norrish's paper, "Border Effects Associated
with Photographic Reversal Processes," I am convinced that they have proven
that halation ("the scattering of light in the film") is the primary cause
of sabatier border effects, though they also state that bromides and
oxidation byproducts may enhance the border effect. In my article
"Controlling the Sabatier Effect" at UnblinkingEye.Com I point out that
"print solarization" might be a good general term for the multiple effects
derived by flashing an emulsion during development--including fog, sabatier
reversal, and border effects caused by diffusion halation.
At first, when reading the Stevens and Norrish article (from the January
1937 issue of THE PHOTOGRAPHIC JOURNAL), I doubted halation took place in
paper at all, as it is so often spoken of as a film phenomenon. Referring to
Mees, S&N state that halation is caused by: "(1) Reflection of the light at
the surface of the crystals, predominant with coarse-grained emulsions." and
"(2) Diffraction at the edges of the crystals, predominant with fine-grained
emulsions." If these are indeed the causes of halation, then I see no reason
why halation should not also take place in a paper emulsion. But we must
bear in mind that all of Stevens' and Norrish's tests were done with plates,
not prints.
On page 21 of the JOURNAL, S&N state, "The production of these photographs
[showing the Sabatier effect] is only made possible by the action of two
separate but closely related facts. Firstly, the developed part of the
plate is desensitized, and secondly this desensitization is extended for a
short distance outside the image of the object." Their paper is concerned
with the second, or so-called border effect. They do not address the cause
of the first effect, desensitization of certain areas of the emulsion. This
desensitization was not effectively addressed until William Jolly, et al.,
published their first paper "An Explanation of the Sabatier Effect" in 1985.
On page 23, Stevens & Norrish report, "We have concluded...that while the
potassium bromide produced in the first development can restrain the second,
the effect is not permanent and can be washed out of the plates. No
Desensitization or destruction of the latent image by potassium bromide has
been found, and...it is possible readily to produce both the Sabattier
effect and the line under circumstances when potassium bromide is not
present." "The line" referred to is of course the Sabatier border effect.
Later in their paper they point out that Sabatier reversal takes place even
with developers that do not cause a release of bromide. They proceed, by
ingenius experiments, to prove that the cause of the Sabatier border effects
must be diffusion halation.
On page 26, S&N state, "...potassium bromide causes no such permanent
desensitization as is found in the Sabattier effect, and no destruction of
the latent image. Any influence that soluble bromides may have on the effect
is almost certainly caused by a local retardation of the development, which
influence is removed by washing the plate before the second development."
Stevens and Norrish are not trying to prove that no bromide reduction is
taking place; rather that bromide is not a primary cause of Sabatier
reversal, which is why they washed their test plates between the first and
second developments. The fact is, with most developers, bromide *is*
produced as a byproduct of development and it *does* have an inhibitory
effect on development where it is present.
On page 25, when S&N discuss the results of their slit experiment, they
note, "...the density of the line at the edge of the heavily exposed slits
is depressed below the density of the point of reversal. This additional
desensitization is almost certainly due to the restraining action of
oxidation byproducts diffusing from the main image." On page 30 they repeat
this assertion: "This additional desensitization is almost certainly due to
the diffusion of reaction products from the main developed image." On page
32, in their summation, they state: "It must be admitted, in view of the
known restraining action of bromides and oxidation products, that the lines
may on occasions be reinforced by this effect...."
In my experience with *print* solarization, the presence of bromide
definitely contributes to the formation of the reversed image. I encourage
this most of the time by *not* washing my prints between the first and
second development. On many occasions I see areas reversing in the tray
during the second development--this is not desensitization of the emulsion
but a destruction of image values created during the first development,
which I believe could only be caused by bromides released during the second
development.
Maybe the reason bromide papers generally work better than chloride papers
is that they release bromides during development rather than chlorides
(which can also act as a restrainer, but perhaps not quite so
efficaciously), though another reason may be that silver bromide grains are
larger than silver chloride grains. I have found one so-called warm tone
paper that solarizes well (though I have no idea the exact composition of
its emulsion): Luminos Classic warm tone fiber.
Ed Buffaloe
http://unblinkingeye.com
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