Phenidone, Metol, and Sharpness
Walt Brand
threads. The discussions have centered around the question of whether
metol-based developers develop more "sharply"-- that is, do they create
more edge effects in a typical emulsion than a similar phenidone-based
developer of equal activity and capacity (a hypothetical situation at
best, but this is a thought experiment I'm putting forth here)?
Briefly, I'm suggesting that it is the far greater sensitivity to
released bromide during the development process that gives metol the
ability to produce developers like FX-1 and Beutler while Phenidone
creates exaggerated edge effects only with very low or no agitation.
Phenidone reacts strongly to its own oxidation products, but these are
in solution, so the developer in bulk creates high densities only with
difficulty or with the addition of superadditive agents like
hydroquinone or ascorbates. Bromide is created in the gelatin around
the crystals of developing AgX, but the Phenidone is relatively
insensitive to this, which explains why benzotriazole is the preferred
antifoggant for Phenidone-based developers.
Metol, on the other hand, is not so sensitive to its own oxidation
product, which, I found on rereading my texts, is itself a developing
agent. Metol, whether used alone or with hydroquinone, is, however,
acutely sensitive to bromide. Bromide released in the gelatin as a
byproduct of development takes awhile to diffuse out, so it forms little
haloes of developer "poison" around developing grains. This is the basis
of the socalled "edge effects".
So both agents can develop sharply, and the bromide-caused edge effects
diminish as development proceeds or with high agitation, but metol has
the edge, so to speak, in its ability to create sharpness enhancement
(and we're talking sharpness or acutance, not resolution, here), all
other things being equal, which of course they never are.
I'm going to see if I can find a ranking of developing agents based on
sensitivity to bromide. Richard Knoppow might have such a table at his
fingertips, and I very much welcome any corrections, data, and further
thoughts that might lead to a world with less bromide drag and greater
sharpness.
Walt Brand
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Before you buy.
Richard Knoppow
>This is in response to a question that's come up in several unrelated
>threads. The discussions have centered around the question of whether
>metol-based developers develop more "sharply"-- that is, do they create
>more edge effects in a typical emulsion than a similar phenidone-based
>developer of equal activity and capacity (a hypothetical situation at
>best, but this is a thought experiment I'm putting forth here)?
>
Good stuff snipped here ....
>
>I'm going to see if I can find a ranking of developing agents based on
>sensitivity to bromide. Richard Knoppow might have such a table at his
>fingertips, and I very much welcome any corrections, data, and further
>thoughts that might lead to a world with less bromide drag and greater
>sharpness.
>
>Walt Brand
>
Thans for the compliment butI don't really, although something like
it is in _Theory of the Photographic Process_ revised edition, C.E.K.
Mees.
Its further complicated because some developer reaction products act
as accelerators. I think this is what happens with Metol-Hydroquinone
type developers. The effects depending somewhat on the activity of the
developer.
If Mike Gudzinowicz is lurking I suspect he may have the real
answer.
---
Richard Knoppow
Los Angeles, Ca.
dick...@ix.netcom.com
SPECTRUM
wrote:
>I very much welcome any corrections, data, and further
>thoughts that might lead to a world with less bromide drag and greater
>sharpness.
>
>Walt Brand
Suggestion 1 : Try Rodinal or a home brewed p-aminophenol
hydrochloride developer.
Suggestion 2 : Consider using a glycin formula such as Edwal
10.
Edwal - 10
Water 750.0ml
Elon 5.0g
Glycin 15.0g
Sod.Sulfite 70.0g
Borax 10.0g
Water to make 1.0 liter
Though it contains Elon, the use of glycin will "smooth out"
the image. BTW, this is probably about 4X as concentrated as you need
with todays films.
Suggestion 3 : Try FX-2
Crawleys FX-2
A
Water 750.0ml
Elon 5.0g
Glycin 15.0g
Sod.Sulfite 70.0g
Water to make 1.0 liter
B
Pot.Carbonate 123.0g
Water to make 1.0 liter
C
Pinacryptol Yellow (1:2000) 100.0ml
Water to make 1.0 liter
Regards,
John
Michael Gudzinowicz
> This is in response to a question that's come up in several unrelated
> threads. The discussions have centered around the question of whether
> metol-based developers develop more "sharply"-- that is, do they create
> more edge effects in a typical emulsion than a similar phenidone-based
> developer of equal activity and capacity (a hypothetical situation at
> best, but this is a thought experiment I'm putting forth here)?
developers to M and MQ developers. For instance, Microphen gives edge
effects comparable to FX-1 which surprised me when I tested them. I don't
have any evidence that developers based on P or derivatives are less
"sharp" or have less of an edge effect than the M equivalent. Metol does
tend to develop fine detail to a higher density which might be related to
adjacency effects, but since P isn't used alone with pictorial films, a
direct comparison is difficult.
> Briefly, I'm suggesting that it is the far greater sensitivity to
> released bromide during the development process that gives metol the
> ability to produce developers like FX-1 and Beutler while Phenidone
> creates exaggerated edge effects only with very low or no agitation.
development times and gamma comparable? With longer development, diffusion
effects are minimized (developer depletion, pH reduction, bromide and
iodide accumulation).
Metol is strongly absorbed to silver grains similar to phenidone, except
at high pH values. Since the bromide effect is due to competitive binding,
they both have nearly the same response to bromide (little response).
Adsorption (micromoles/m^2)
pH 8.3 10 10.85
Hydroquinone none 0.5 0.5
Metol 1.0 0.9 0.25
Phenidone 0.7 1.3 1.6
Usually, the effect of no agitation is bromide drag and/or developer
streaking near border areas which is on a gross visible scale compared to
the border and fringe effects. That effect is best avoided, since it is
directional in character (usually downward) and not related to fine detail.
The border and fringe effects are confined to a few microns along the edge
gradient, and agitation has little effect on them. The primary transport
mechanism is diffusion through the gelatin to adjacent areas, with some
diffusion occurring in the laminar layer.
Note that your bromide hypothesis is very easy to test simply by adding a
low concentration of bromide to a developer, and adjusting pH for speed,
time and contrast. The local variations in bromide concentration would be
swamped out by the bromide in solution which may or may not change acutance.
The potent restrainer iodide has been added to a number of developers to
_increase_ "sharpness". Art Kramer used iodide with Beutler's developer,
and Geoffrey Crawley used it in FX-1, which you mention, and FX-13. I
don't know whether the effect was due interference with the bromide
gradient at the edge or not, but I suspect that the restrainer was
included to inhibit development of grains which were weakly exposed by
scattering deep in the emulsion, so it is a "surface" effect. You might
ask Art about it.
One rarely sees a decrease in development (fringe effect) at the low
density side of a border, which one would expect if inhibitor diffusion
were an important factor.
> Phenidone reacts strongly to its own oxidation products, but these are
> in solution, so the developer in bulk creates high densities only with
> difficulty or with the addition of superadditive agents like
> hydroquinone or ascorbates. Bromide is created in the gelatin around
> the crystals of developing AgX, but the Phenidone is relatively
> insensitive to this, which explains why benzotriazole is the preferred
> antifoggant for Phenidone-based developers.
>
> Metol, on the other hand, is not so sensitive to its own oxidation
> product, which, I found on rereading my texts, is itself a developing
> agent. Metol, whether used alone or with hydroquinone, is, however,
> acutely sensitive to bromide. Bromide released in the gelatin as a
> byproduct of development takes awhile to diffuse out, so it forms little
> haloes of developer "poison" around developing grains. This is the basis
> of the socalled "edge effects".
Metol, as well as phenidone, is inhibited by development products which is
one reason why they are used in compensating developers. Hydroquinone and
other polyphenols have increased development activity in the presence of
their oxidized products. That is not to say that the latter can not be
used as compensating developers if diluted. The primary requirement is a
low level of developing agent which is quickly oxidized in areas of high
density resulting in local depletion. There may be other mechanisms with
different formulations. Microdol-X's compensating effect may be due to
oxidation products and decreased coverage due to smaller grain size.
Bromide would have little or no effect in that type of developer which is
very well restrained.
> So both agents can develop sharply, and the bromide-caused edge effects
> diminish as development proceeds or with high agitation, but metol has
> the edge, so to speak, in its ability to create sharpness enhancement
> (and we're talking sharpness or acutance, not resolution, here), all
> other things being equal, which of course they never are.
>
> sensitivity to bromide. Richard Knoppow might have such a table at his
> thoughts that might lead to a world with less bromide drag and greater
> sharpness.
which exhibits bromide drag isn't worth doing under any circumstances.
Some developers, such as PMK, exhibit very high acutance and border
effects and require nearly constant agitation to avoid streaking. Although
tanning my help the edge effects along, metol is still the primary
developing agent, and "stand" development will only ruin the negatives.
Apart from the obvious (stability, fog, speed, etc.) one of the primary
differences between metol and phenidone is the threshold pH value required
to initiate developing action. For metol, the pH value to be exceeded is
7.25; for phenidone, it is 6.0. One could design a developer which
operates near the threshold value and is weakly buffered. Hydrated protons
are released during development, and a local decrease or increase in pH at
the border could inhibit or enhance development in a manner similar to
that which you propose for bromide.
However, most if not all of the "high definition" developers rely on a
high pH and low developer concentration to cause local depletion. That
seems to be the preferred approach, along with dilution of commercial
developers.
Below, I've included tables from an article by Altmann and Henn which
compared fine grain and high definition developers using Panatomic-X and
Tri-X films (Pho. Sci. and Eng.,5:129(1961)). It illustrates a few points.
First, in the Panatomic-X table, as developing agent concentration is
reduced, acutance and granularity increase for the fine grain film. Also,
low sulfite enhances acutance and speed, as one might expect. Note that
the times increase with increasing acutance. The longer times to get the
same gamma permit diffusion to reduce local bromide accumulation and pH
differences. The primary driving force for the edge effects would seem to
be local depletion and replenishment resulting in greater local developer
concentrations.
The results for Tri-X are quite different. Acutance is not enhanced,
though granularity increases through the high definition series. Also, the
fine grain series doesn't work well with this film.
I don't know the reason for this behavior, though I've been aware of the
admonition not to use acutance or solvent developers with traditional high
speed films.
Apart from attesting to excellence of D-76 1:1, the data suggests that
effects are highly dependent upon the emulsion and grain characteristics,
which tends to undermine any generalizations.
From Altman and Henn:
Series Number Metol Sulfite Bisulfite Total Sulfite Kodalk
g/l g/l g/l M/l g/l
I. AH-1 7.5 10 0 0.08 4
Fine AH-2 7.5 30 5 0.29 0
grain AH-3 7.5 100 15 0.95 0
AH-4 7.5 200 20 1.8 0
II. AH-15 2.5 10 0 0.08 4
High AH-16 1 10 0 0.08 6
Sharp- AH-17 0.5 10 0 0.08 20
ness AH-18 0.25 10 0 0.08 20
Speed, Acutance and Granularity of Panatomic-X
Dev. Contrast Speed Acutance Granularity
Series Number Time gamma % % %
I. AH-1 9 0.62 130 106 123
Fine AH-2 8 0.63 125 100 86
grain AH-3 8.25 0.63 82 100 50
AH-4 11 0.63 96 84 55
II. AH-15 4 0.62 107 113 155
High AH-16 5 0.61 117 116 164
Sharp- AH-17 7 0.69 129 125 164
AH-18 13 0.64 150 141 155
Control
D-76 1:1 6.5 0.62 100 100 100
Speed, Acutance and Granularity of Tri-X
Dev. Contrast Speed Acutance Granularity
Series Number Time gamma % % %
I. AH-1 22 0.62 128 79 132
Fine AH-2 20 0.67 107 96 114
grain AH-3 16 0.65 70 58 89
AH-4 20 0.64 62 42 89
II. AH-15 11 0.62 100 75 147
High AH-16 11.5 0.62 94 75 150
Sharp- AH-17 26 0.67 94 88 154
ness AH-18 35 0.62 87 96 161
Control
D-76 1:1 8.5 0.63 100 100 100
Walt Brand
find statements you disagree with, but the data tables are useful for
many future projects, and the dialectic is, after all, why we're all
here.