The edge effect is certainly evident in the FX-2 example. The area just around the cross is noriceably lighter. Due to the nature of the subject it's hard to determine the relative sharpness between the two images. However if you look at the small lighter detail in the far lower right of both images the FX-2 images does appear to be sharper.
Last edited by Gerald C Koch; 01-03-2013 at 01:43 PM. Click to view previous post history.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.
~Antoine de Saint-Exupery
Perceived sharpness (acutance) in the final print itself is generally superior with a tanning developer because of improved edge effect. This is readily detected just by normal viewing, and has nothing to do with mysticism or pyro wars. It's a simple fact a kid can spot who's too young to even read.
It applies equally to all formats, given a comparable degree of typical enlargement from the same type film and same amt of development. Beyond this, there are way too many potential variables to give a pat answer, as well as atypical cases where you might not want these characteristics.
The reason commonly given to explain the purportedly stronger edge effects with Pyro (note I'm speaking strictly of Pyro for now, not Cathechol) is that the tanned gelatin does not as readily allow the "escape" of bromide by-products. However again it seems to me there should also be an offsetting effect since the tanned gelatin should also limit the migration of developer and development by-products within the gelatin. In fact this is one of the features that is supposed to give Pyro a resolution advantage (less infectious development etc). So again it seems like writers such as Hutchings pick and choose the positive attributes.
I've gone back to some texts regarging the Tanning/Staining issue and will post some notes here. Inconclusive as usual. There are apparently two "stages" of tanning etc. Some of it seems to come down to semantics. More to come.
Appreciate all the feedback so far. Again I'm not for or against in any way. Just trying to flesh out a few things in the literature. PMK and WD2D+/H+ are fine developers in my experience - although they seem heavily film-dependent (for example I've found WD2D+ to work very well with FP4+ but give a massive speed loss with Delta). As for Pyrocat, I have never used it so I can't say anything about it or how it works.
Regarding Alan's test - I'd like to know a little more about the methodology. Agitation etc.
Last edited by Michael R 1974; 01-04-2013 at 09:02 AM. Click to view previous post history.
Tanning is only part of the equation. The other pertinent half is the image stain, which can be brownish, yellow-green, etc. By specific dev choice and mating it to an appropriate paper, quite a
bit of control can be obtained, esp w/VC papers. Discussing all the potential nuances will in fact lead
one into "pyro wars". A lot depends upon what you are trying to achieve. There are a lot of good
pyrog. and pyrocat formulas out there right now, and a degree of experimentation with several of
them will lead to answers a lot faster than tracing all the past quarrels. But specifics require a specific dev in question to begin with. The chemical effect really has nothing to do with "dye clouds"
as in color photog.
I forgot to add ... there is in fact a lot of older literature on the nature of infectious development
and tanning. Technicolor and dye transfer were both tanning dependent. It's quite a complex topic, actually.
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Agree. Complex indeed.
The original question concerned the dye clouds (stain) formed around the developed silver, and whether there is a noticeable loss of resolution associated with this to offset the supposed "grain masking" effect. The grain masking effect of the spreading dye is an often quoted benefit, but there is never any mention of the price you pay. Even heavily staining formulas are still touted as high resolution and acutance developers. There are valid reasons for this, but there are some inconsistencies in the literature. Then we got into tanning vs staining and whether or not they are the same process. In compiling info from a few sources (obviously not exhaustive and subject to challenge) the answer is not clear. I'd like to limit the discussion to Pyro and Pyro-Metol specifically, but since Pyrocat is such a popular developer it may be worth considering even though it is quite different. I put forth some general notes on tanning/staining developers below, followed by some excerpts related specifically to tanning/staining action:
Reasons given for high resolution, definition, acutance
1. Tanning of gelatin: less silver "migration", less infectious development, promotes surface action, prevents "escape" of development by-products (see edge effects)
2. Lower silver density in developed negative
3. Edge effects due to controlled exhaustion (low sulfite, low developer concentration) and tanning which promotes retention of development by-products
4. Minimal solvent action
Reasons given for lower graininess vs non-tanning high definition developers
1. Less developed silver density
2. Less grain "clumping" due to tanning action
3. Grain masking from dye spreading into spaces between developed silver grains/particles
Some of these things would appear to be at odds, as mentioned above. For example, if tanning inhibits migration and diffusion to increase resolution, how can it also promote increased border/fringe effects? Similarly, if the dye spreads beyond the edges of the silver grains to fill in some space, how can this not negatively impact resolution/definition?
Here are some notes regarding tanning and staining action (not all consistent of course )
"In developers containing low concentrations of preservative, the oxidation products of pyrogallol development produce a...stain". "The oxidation products from pyrogallol development also tan the gelatin in the areas of image formation. Increasing the preservative in the developing solution inhibits the staining and tanning actions of the developer." Haist p.175
"The partially or completely oxidized forms of some developing agents react readily with the gelatin surrounding a crystal of silver halide undergoing reduction." Haist p.507
"A tanning developing agent must be used that has oxidation products that are capable of diffusing a considerable distance before reaction with the gelatin."Haist p.509
"Pyrogallol tanning developers...cannot contain much sulfite, as this preservative destroys the tanning action."Haist p.510
"Stain image formation is distinct from the formation of a tanned relief image. Stain results from two or more developer molecules reacting together in an oxidizing medium to yield a coloured, insoluble product that is retained, imagewise in the gelatin.""Gelatin tanning occurs when the oxidized developer molecule reacts with a gelatin molecule in an oxisizing medium."Haist p.516
"During the development process pyro begins hardening the film gelatin immediately and separately from the actual silver reduction process"."Investigations confirm that tanning takes place in two distinct stages: a rapid primary hardening and then a slow secondary stage caused by the retention of the developer oxidation products formed as the silver halide is reduced. The tanning products formed as pyro reduces the silver halides first form in discreet cavities around the silver grains (C.E.K. Mees & T.H. James, 1966). These oxidation products undergo further polymerization and cross-linking with the gelatin." (Hutchings p.53)
"Pyrogallol has a reputation for producing the strongest edge effects of any developer. Pyro and metol are both affected by bromide ions. The rapid surface hardening of the gelatin by the pyro apparently retards bromide ion diffusion out of the emulsion during film development." (Hutchings p.55)
"Oxidation of the pyro causes two different types of negative stain. Contact with free oxygen in the developer or the air causes pyro to oxidize. This aerial oxidation discolours the developer and has a tendency to cause general or fog stain in the negative. The second type of stain is a complex polymerized oxidation product iin association with the cross-linked gelatin molecules (Tull, 1963). This is the image stain and is formed in situ with the reduced silver (Baker, 1941). This stain is caused by either direct silver reduction by the pyro or by its reactivation of other developing agents..." (Hutchings p.55)
"Tanning hardens in proportion to the amount of silver deposited during development. This causes the film to dry at different rates, accordiing to image density. The result is an adjacency effect unique to tanning developers which increases sharpness." (Anchell/Troop p.73)
"A secondary effect of tanning developers is staining of the image with a permanent dye that is created by the reaction products. Although staining goes hand in hand with tanning, it is a separate phenomenon." (Anchell/Troop p.73)