[pure-silver] Re: Good news from Ilford
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Mon, 11 Jul 2005 16:39:23 -0700
----- Original Message -----
From: "David Swinnard" <davidswinnard@xxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, July 10, 2005 5:22 PM
Subject: [pure-silver] Re: Good news from Ilford
Richard, I am assuming the Microdol X is still available -
I just
haven't seen it recently around here (though I do admit to
not actively
seeking it so maybe my blinders are on...)
You mention dichro fog... Is D-23 susceptible to this?
I've been using
the Perceptol at 1+3 for sharpness with Acros so perhaps
just plain old
D23 (diluted) will do the trick.
I like the FX-39 but can't justify running to Seattle for
it (and having
it shipped across the border runs the cost way up -
everybody who
touches it wants their cut.)
Dave
D-23 does not seem to have the same problem with dichroic
fog that the extra-fine-grain developers do. Dichroic fog is
a deposit of metallic silver all over the negative. The
silver comes from the emulsion and is the result of the
relatively large amount of silver halide solvent action of
the fine grain developers. D-25, for instance, is D-23
buffered to neutral pH. Metol still develops at neutral pH
but slowly. The extra fine grain property of D-25 is partly
due to the long time of development during which the Sodium
Sulfite can work on the halide grains and is partly due the
lack of emulsion swelling. It may have other factors also.
Microdol-X is similar to D-25 but contains Sodium chloride
as a fine grain agent. Grant Haist mentions this in _Modern
Photographic Processing_ but not in much detail. I don't
fully understand how the sodium chloride functions to reduce
the graininess. Nonethless, Microdol has a similiar problem
with having a large quantity of dissolved silver halide in
it which can be converted by the developer into metallic
silver and deposited on the negative. Microdol-X appears to
have a sequestering agent to keep the silver in solution.
Again, Haist mentions this but does not go into detail other
than to speculate that the agent may be a Mercaptan.
Other very fine grain developers also have problems with
dichroic fog, particularly the old formulas using Para
phenylenediamine. PPD is a silver halide solvent itself.
This is one reason for its very fine grain development. Note
that these solvents do not dissolve the developed silver
grains but rather affect the way the silver crystals develop
from the exposed halide grains. Keeping the pH near neutral
tends to minimize migration of developed silver crystals
toward each other, an effect known as clumping. This is
related to softening and swelling of the gelatin. The pH for
minimum swelling of photographic gelatin is near neutral pH.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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