Superadditive amidol developers?

michael_r said:

Regarding reaction/oxidation products of amidol, there is a brief reference in Haist to research (again, extremely old however) suggesting an oxidation product is produced which acts as a desensitizer, lessening fog. Of course this likely depends on the conditions (pH, sulfite concentration etc.). Another study reported improved stability of amidol in an amidol-PPD-sodium bisulfite developer. However given how different the emulsions of the day were in comparison with contemporary films/papers, most of this early-mid 20th century research is of limited relevance.

Another old preservation technique for amidol solutions was the use of tin compounds. Funny enough Hutchings includes this as an option concerning the addition of small amounts of amidol to PMK stock solution A. Again though, his sources are very old and way out of date.

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It also seems to pop up in/ around some aspects of colour processing around the mid-20th century - and possibly as a feedstock for other synthesis. Given that the stain product seems to be a dye formed via oxidation (and it has been used as a dye as such), I wouldn't be surprised if it had been well investigated with regards to colour processes and, more importantly, its behaviour within multilayer/ blended emulsion structures (where it may well have been found wanting).

Rudeofus said:

In terms of cost or ease of use it will hardly beat PQ developers. Yes, P + HQMS are great for film, but this combo is hardly cost effective for printing. I guess the hope was to preserve some of the attractive properties of Amidol (image tone, low pH), while avoiding its annoying properties (staining, short shelf life). Yes, DTPA or ATMP would be great addition.

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Given that HQMS is effectively formed in-situ anyway, and what seems to be known (within manufacturing R&D at least) about the inhibition effects of phenidones - along with how this can be manipulated within the P:Q ratio (as opposed to metol's exhaustion effects, which are eliminated on adding HQ), an array of contrast (and some colour, to an extent) outcomes seem quite readily achievable via that route (given enough analytical backup). I've never been quite sure what clearly defines the supposedly 'ideal' colour characteristics of Amidol - other than it possibly effectively forming a dye image with Azo etc thus conferring the appearance of warmth - especially as a number of other developers are known to be able to get warmer results out of chloride papers. On the other hand, the 'classic' amidol formulae are claimed to give cold tone results with higher bromide content papers, which tends to suggest that there may be a specific (oxidation?) effect relative to the available surface area of particular grain structures that can react to the developer. The level of sulphite in some Amidol developers is probably high enough to start having a mild monobath effect on the relatively simple very high chloride content emulsions like Azo, hence the desire for a highly active & rapid developing agent (and thus the tendency of Ilford, Kodak etc to recommend double strength paper developer for contact papers to get image build-up ahead of the sulphite kicking in).

Lachlan Young said:

Given that the stain product seems to be a dye formed via oxidation (and it has been used as a dye as such), I wouldn't be surprised if it had been well investigated with regards to colour processes and, more importantly, its behaviour within multilayer/ blended emulsion structures (where it may well have been found wanting)

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The dyes formed in staining developers are AFAIK quite different from dyes formed in color materials.

Lachlan Young said:

Given that HQMS is effectively formed in-situ anyway, and what seems to be known (within manufacturing R&D at least) about the inhibition effects of phenidones - along with how this can be manipulated within the P:Q ratio (as opposed to metol's exhaustion effects, which are eliminated on adding HQ), an array of contrast (and some colour, to an extent) outcomes seem quite readily achievable via that route (given enough analytical backup).

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HQMS is formed during development in developers containing HQ, yes. According to private communication with PE the attractiveness of HQMS comes from the inactivity of its oxidation products, which lead to better sharpness - a compelling argument for film developers but hardly one for print devs. If oxidized Amidol indeed lowers pH to the point of restraining action as claimed by Ashley, and if its mobility is high enough to create noticeable Mackie lines in final prints, then it may have merit anyway.

Rudeofus said:

If oxidized Amidol indeed lowers pH to the point of restraining action as claimed by Ashley, and if its mobility is high enough to create noticeable Mackie lines in final prints, then it may have merit anyway.

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In this regard I was saying oxidized amidol may be an organic restrainer (like many dyes are) but more importantly, ascorbate radicals are known to be more acidic than ascorbic acid and have a restraining action, and is also much more stable than many other radicals, it can be kept in relatively stable solution at a particular pH (can't remember, iirc something like 3-5). Being able to potentially make use of these two properties due to amidol being a very active developer at acidic pH, I believe there is some potential as.a developer. Maybe more so toward film developer than print developer, though I expect many properties can be gathered from using it as a paper developer. If it could be proven stable, then maybe it could be useful as a film developer

grainyvision said:

In this regard I was saying oxidized amidol may be an organic restrainer (like many dyes are) but more importantly, ascorbate radicals are known to be more acidic than ascorbic acid and have a restraining action, and is also much more stable than many other radicals, it can be kept in relatively stable solution at a particular pH (can't remember, iirc something like 3-5). Being able to potentially make use of these two properties due to amidol being a very active developer at acidic pH, I believe there is some potential as.a developer. Maybe more so toward film developer than print developer, though I expect many properties can be gathered from using it as a paper developer. If it could be proven stable, then maybe it could be useful as a film developer

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If you plan on testing Amidol for film developers, then you have to primarily check its resulting ISO speed. All the sharpness and grain differences you can ever dream of will be less than the difference between ISO100 and ISO200 films using roughly the same technology. Therefore all the grain&sharpness improvements mean nothing if they come with a half stop speed loss against a PQ/PC/PQMS type developer.

If you plan on testing Amidol for print developers, then the width of the Mackie lines is important, and this width depends on diffusion speed of the oxidized Amidol. There is no point in 10µm wide Mackie lines in a print developer, however useful they are in a film developer.

Rudeofus said:

The dyes formed in staining developers are AFAIK quite different from dyes formed in color materials.

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For what it's worth, I recall that the toxicological studies done on Amidol regard it as similar in action to PPD/ substituted PPD's in the way it'll form a dye - oxidatively. At the end of the day, all the staining developers are essentially producing a dye coupled image - such that you could bleach out the silver - however the 'stain'/ dye seems to be regarded as being of uncertain longevity.

Rudeofus said:

HQMS is formed during development in developers containing HQ, yes. According to private communication with PE the attractiveness of HQMS comes from the inactivity of its oxidation products, which lead to better sharpness - a compelling argument for film developers but hardly one for print devs. If oxidized Amidol indeed lowers pH to the point of restraining action as claimed by Ashley, and if its mobility is high enough to create noticeable Mackie lines in final prints, then it may have merit anyway.

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Yes, but that's only part of the picture (terrible pun, I know) - and while there are warnings (in the literature) about designing in excessive adjacency effects in processes that would potentially go through multiple duplication steps between camera and viewer, inhibition effects can also have potentially useful impacts elsewhere - shoulder shape, for example . And it's worth noting too that phenidones on their own produce dramatically stronger adjacency effects (at the cost of poor coverage - ie accessing only some of grain that's then developed a lot) - it seems to be through balancing the level of a phenidone, relative to HQ/ HQMS etc that delivers both good coverage & a range of options of inhibition effects (and that's before considering the effects of the inhibitors that can be released from the emulsion - or solvency effects from the developer). There does appear to be an Agfa developer disclosed in the 1990s that seems to be aimed at preventing inhibition effects yet still accessing all the silver in the emulsion (though that's wandering some way away from this discussion as the Agfa developer relates to reversal processing).

Lachlan Young said:

For what it's worth, I recall that the toxicological studies done on Amidol regard it as similar in action to PPD/ substituted PPD's in the way it'll form a dye - oxidatively. At the end of the day, all the staining developers are essentially producing a dye coupled image - such that you could bleach out the silver - however the 'stain'/ dye seems to be regarded as being of uncertain longevity.

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Can you tell me for sure, that the staining reaction in a pyro developer is essentially the same type of reaction as what we see in regular color couplers?

PS: I find your remarks on phenidones very interesting and definitely worth discussing, but would prefer to do this in a separate thread.