Okay, how does alkaline stop bath actually work?

Donald Qualls · Sep 19, 2022

I found a video from John Finch (Pictorial Planet on YouTube) touting his recently released line of developers as well as an alkaline fixer and alkaline stop bath. I know all-alkaline process is preferred for pyrogallol and pyrocathechin staining/tanning developers, because it increases the level of stain (or stain retention, anyway), which masks grain in printing or allows the same negative to scan well and also make good alt-process (UV sensitive) prints.

What I don't understand is how an alkaline stop can possibly do even as much as water stop -- acid stop does its job by shifting the pH in the emulsion low enough to inactivate the developing agent(s), and water stop works by diluting the developing agent, effectively washing it out of the gelatin over a short period of time. The only mechanism I can see for an alkaline stop to have any advantage over water stop, however, would be a chemical antagonist that neutralizes the developing agent -- and to be generally applicable, this would have to be the case for developers like pyrogallol and pyrocatechin, but also for p-aminophenol, metol, phenidone/dimezone, PPD -- but presumably not Amidol, which can be active in acidic pH.

So, what am I missing? Is the alkaline stop just "faster water", keeping the gelatin porous to be able to wash out the developing agent faster than water, or is there some weird organic chemistry going on here?

Alan9940 · Sep 19, 2022

Waiting with baited breadth to hear replies to your question! Personally, an alkaline stop just seems like it could be "faster water." I suppose it supports the pervasive theory that any staining regimen needs to be maintained alkaline throughout all steps. I've used several different staining formulas over the years and have used half-strength acid stop as well as normal acidic fixers in my development process, and I've never noticed any degradation to the image stain. I'll admit that I have no way to prove this scientifically, but the resulting prints look the same.

john_s · Sep 19, 2022

I suppose we don't hear about alkaline stop because they don't work and we don't need them anyway. I think there was some mention the Film Developing Cookbook.

It's there on page 120. I'm away without scanning equipment. I can copy it for you in a few days.

john_s · Sep 19, 2022

I forgot I had a scanner in my pocket. The authors still don't say what the point is.

Jay Schrotenboer · Sep 19, 2022

john_s said:
I forgot I had a scanner in my pocket. The authors still don't say what the point is.View attachment 316740

That sounds like a lot of trouble to go through for a stop bath.

pentaxuser · Sep 19, 2022

What I don't understand is how an alkaline stop can possibly do even as much as water stop --

Donald Qualls said:
So, what am I missing? Is the alkaline stop just "faster water", keeping the gelatin porous to be able to wash out the developing agent faster than water, or is there some weird organic chemistry going on here?

Yes this whole subject must be one of the least discussed on Photrio so like you I'd love to be able to get to the bottom of this

I know some might say I see "marketing speak" where others do not but I think I can say that this alkali stop bath is a truly unique product so deserves closer examination

pentaxuser

Raghu Kuvempunagar · Sep 19, 2022

john_s said:
I forgot I had a scanner in my pocket. The authors still don't say what the point is.View attachment 316740

Using Sulphite in a stop bath is not a great idea for staining developers as it can affect the stain.

Donald Qualls said:
What I don't understand is how an alkaline stop can possibly do even as much as water stop -- acid stop does its job by shifting the pH in the emulsion low enough to inactivate the developing agent(s), and water stop works by diluting the developing agent, effectively washing it out of the gelatin over a short period of time. The only mechanism I can see for an alkaline stop to have any advantage over water stop, however, would be a chemical antagonist that neutralizes the developing agent -- and to be generally applicable, this would have to be the case for developers like pyrogallol and pyrocatechin, but also for p-aminophenol, metol, phenidone/dimezone, PPD -- but presumably not Amidol, which can be active in acidic pH.

So, what am I missing? Is the alkaline stop just "faster water", keeping the gelatin porous to be able to wash out the developing agent faster than water, or is there some weird organic chemistry going on here?

pentaxuser said:
What I don't understand is how an alkaline stop can possibly do even as much as water stop --

Alkaline stop baths can be designed to work for some developing agents that have high threshold ph. The idea is to use an alkaline buffer that has pH lower than the threshold pH of the developing agent. For example, Catechol has a threshold pH above 9 and hence a borate buffer of pH around 8 should work as an alkaline stop bath for Pyrocat HD. Whether such a stop bath better than water is a different question. However, as water is poorly buffered compared to a borate buffer, it is reasonable to expect that the development stops earlier in the alkaline stop bath than in water.

Haist discusses an interesting application of a buffered stop bath - temporary stopping of development for inspection.
"Aerial cine films are also inspected during development to insure correct development because only one exposure of the scene taken is available. A stop bath for temporarily halting development during the inspection period was proposed by Vere Maffet and Earl Delzon in U. S. Patent 3,284, 199 (1966). Typical fine-grain, general-purpose, lithographic, or X-ray developing solutions have pH values in the range of 8.5 to 10.5. Such developers would be inactive below pH 8.0. One suggested buffered stop bath consisted of 6.80 g potassium dihydrogen phosphate dissolved in 900 ml water. Sodium hydroxide was added until the pH was 7.20, then the solution made up to 1000 ml with water. Another bath consisted of 80 g boric acid crystals dissolved in 900 ml water, adjusted to pH 7.20 with sodium hydroxide, and then made to 1000 ml with water."

reddesert · Sep 19, 2022

pentaxuser said:
What I don't understand is how an alkaline stop can possibly do even as much as water stop --

The developing reaction is a reduction reaction, where a silver halide is reduced to metallic silver. (Reduction = opposite of oxidation.) The silver halide is something like AgX (now you know where AgX gets his name) where X is Cl, Br, or I, and the silver halide crystal is made up of Ag+Br- ions, or chloride, or iodide. When some photons strike the silver halide they cause a latent image center of metallic silver.

It's not simple, but in a very crude explanation, an alkali environment has free OH- ions, which combine with the developing agent to produce a developing agent with a negative ion that reduces the Ag+ (surrounding the latent image center) to metallic silver. The halide ion such as Br- is left over, thus halide ions are a development byproduct. They act to reduce the activity of the developer; if there are already halides in solution, the chemical reaction that produces more halides is disfavored.

A restrainer such as potassium bromide keeps the developer from attacking non-exposed silver halide crystals, so that it doesn't fog the entire film. Effectively, adding restrainer limits development action similarly to exhausting the developer.

So if you want to stop development, approaches include:
1. acid stop bath, preventing the ionization of the developing agent
2. water bath, diluting the developer
3. dumping in a ton of restrainer, interfering with the reduction reaction.
This alkaline stop bath falls under #3.

albada · Sep 20, 2022

reddesert said:
So if you want to stop development, approaches include:
1. acid stop bath, preventing the ionization of the developing agent
2. water bath, diluting the developer
3. dumping in a ton of restrainer, interfering with the reduction reaction.

Would a neutral (~pH7) buffer-system work better than a water bath (#2)? I suspect it would dilute developer like water, but also quickly halt development by dropping pH below the developer's threshold. But I'm no chemist...

Raghu Kuvempunagar · Sep 20, 2022

albada said:
Would a neutral (~pH7) buffer-system work better than a water bath (#2)? I suspect it would dilute developer like water, but also quickly halt development by dropping pH below the developer's threshold. But I'm no chemist...

As I mentioned in my previous post, Haist Vol 1. page 552 talks about the use of a buffered stop bath of pH ~7 for temporarily stopping development of certain types of film for the purpose of inspection. Apparently, such stop baths stopped development faster than water:

"After development was in progress, the film was immersed for 20 sec in the buffered stop bath, inspected for 60 sec on a safelight table, then returned to the developer, if necessary."

Donald Qualls · Sep 20, 2022

Raghu Kuvempunagar said:
80 g boric acid crystals dissolved in 900 ml water, adjusted to pH 7.20 with sodium hydroxide, and then made to 1000 ml with water.

Doesn't distilled water run between 7.0 and 7.2? All this is, then, is buffered water, and it's "alkaline" only by strict definition.

The idea of using borax to be distinctly alkaline but not enough so for development to continue seems likely -- but it would only work with pyro and catechol based developers (and maybe not even with PMK, for instance, which contains metol that would still maintain some activity at pH 8.0 -- which is the lower limit for sulfite solution as in D-23). Given Finch is selling only pyro and pyrocatechin base developers (Thornton formulae), this (borate buffer at pH 8.0) seems likely.

pentaxuser · Sep 20, 2022

pentaxuser said:
What I don't understand is how an alkaline stop can possibly do even as much as water stop --

Yes this whole subject must be one of the least discussed on Photrio so like you I'd love to be able to get to the bottom of this

I know some might say I see "marketing speak" where others do not but I think I can say that this alkali stop bath is a truly unique product so deserves closer examination

pentaxuser

Can I clarify for those attaching my name to the first sentence above. This was part of Donald's quote which I had used to make my point from "Yes" onwards but somehow this part of Donald's quote became separated and ended up appearing to be mine.

pentaxuser

Andrew O'Neill · Sep 20, 2022

Sounds like a lot of fuss for a stop bath, but what do I know? I've never had issues with acid stop baths affecting stain from pyro developers. I am planning to conduct a more thorough test with pyrocat-hd, and new to me 510-pyro.

albada · Sep 20, 2022

Raghu Kuvempunagar said:
As I mentioned in my previous post, Haist Vol 1. page 552 talks about the use of a buffered stop bath of pH ~7 for temporarily stopping development of certain types of film for the purpose of inspection. Apparently, such stop baths stopped development faster than water:

"After development was in progress, the film was immersed for 20 sec in the buffered stop bath, inspected for 60 sec on a safelight table, then returned to the developer, if necessary."

I should have read the pH numbers in your posting more carefully. Sorry.
I use a water stop, which works fine. My dev-times accommodate the water-stop, which brings up a question: If your dev-time accounts for a water-stop, then what is the benefit of quickly stopping development?

pentaxuser · Sep 20, 2022

Andrew O'Neill said:
Sounds like a lot of fuss for a stop bath, but what do I know? I've never had issues with acid stop baths affecting stain from pyro developers. I am planning to conduct a more thorough test with pyrocat-hd, and new to me 510-pyro.

Yes it sounds like a lot of fuss to me as well, Andrew but there is the cost to benefit aspect as well. The alkali stop bath in question states it does 60 films so at £23.00 per bottle this works out to 38 pence per film for a process that no-one seems to know how much quicker an alkali stop is compared to water.

There have been threads on water v acid stop on Photrio some while ago but from what I can recall it would seem that for staining developers the development time is of a sufficient length to mean that a water bath acts quickly enough

So on a cost to benefit basis this alkali stop bath is very expensive assuming it is quicker in acting to make a real difference to the time to which the film is subject to even a tiny amount of extra development

pentaxuser

Donald Qualls · Sep 20, 2022

pentaxuser said:
on a cost to benefit basis this alkali stop bath is very expensive

I hadn't even looked at cost. The only staining developer I've used is Caffenol (and the version with ascorbate virtually doesn't stain); I've used it with water stop because carbonate accelerator is prone to produce emulsion pinholes in acid stop (especially in a Fomapan I use for most purposes).

I was purely curious how an alkaline bath could stop development, and it appears the most likely mechanism is lowering pH to a still-alkaline level that's none the less not alkaline enough for the developer to continue to work. If I need this for some reason, then, I'll probably just get a pH meter and make a borate buffer solution at pH 8 or a little lower. Seems easy enough, and I have borax and sodium hydroxide on hand (and can get boric acid fairly easily).

Raghu Kuvempunagar · Sep 20, 2022

albada said:
I should have read the pH numbers in your posting more carefully. Sorry.
I use a water stop, which works fine. My dev-times accommodate the water-stop, which brings up a question: If your dev-time accounts for a water-stop, then what is the benefit of quickly stopping development?

This is what Haist (Vol 1, Chapter 12, page 540-541, says about water stop baths:

"Image formation may be brought slowly to a stop by immersing the photographic material in water. Water stop baths of 30 to 60 sec duration have often been recommended, especially following a fine-grain or high-definition developer of low alkalinity. In this case the water bath acts as the second bath of a two-bath developer. However, image nonuniformity may result from the use of a water stop bath following development in a highly energetic buffered developer of high pH. An acidic stop bath is required in this case because development is stopped more quickly by the neutralization of alkali of the remaining developer, inactivating the developing agents."

Now,

1. Pyrocat-HD type developers are high pH developers as they use Carbonate as the alkali.

2. Acid stop bath is not advised by the inventors and manufacturers of Pyrocat-HD type developers as they fear it will affect the stain. There are also reports of pinholes forming when an acid stop is used with Pyrocat-HD type developers that use Carbonate as the alkali.

3. Going by Haist, water stop bath might not be ideal for Pyrocat-HD type developers. Further, water is poorly buffered and hence pH change due to water stop is likely to be non-uniform and unpredictable. So this could potentially result in non-uniform stain. However, in practice, several practitioners who do use water stop with such developers seem to notice no image nonuniformity.

4. If users of Pyrocat-HD type developers don't want to use either water stop or acid stop for the fears of image non-uniformity, stain degradation, and pinholes, alkaline stop bath is the only alternative.

5. Peter Hogan's alkaline stop bath, reintroduced by John Finch of Pictorial Planet, is targeted for such people - those users of Pyrocat-HD type developers who fear water and acid stops will degrade image quality of their stained negatives.

Raghu Kuvempunagar · Sep 20, 2022

pentaxuser said:
no-one seems to know how much quicker an alkali stop is compared to water.

This is a great question that should be asked to John Finch and a question that he should answer.

Raghu Kuvempunagar · Sep 20, 2022

Donald Qualls said:
If I need this for some reason, then, I'll probably just get a pH meter and make a borate buffer solution at pH 8 or a little lower. Seems easy enough, and I have borax and sodium hydroxide on hand (and can get boric acid fairly easily).

For Catechol based developers, Borate buffer is attractive as stop bath as Catechol and Borates form a complex that is much less active than Catechol. In combination with pH reduction, this should effectively stop development quickly.

john_s · Sep 21, 2022

Raghu Kuvempunagar said:
This is what Haist (Vol 1, Chapter 12, page 540-541, says about water stop baths:

"Image formation may be brought slowly to a stop by immersing the photographic material in water. Water stop baths of 30 to 60 sec duration have often been recommended, especially following a fine-grain or high-definition developer of low alkalinity. In this case the water bath acts as the second bath of a two-bath developer. However, image nonuniformity may result from the use of a water stop bath following development in a highly energetic buffered developer of high pH. An acidic stop bath is required in this case because development is stopped more quickly by the neutralization of alkali of the remaining developer, inactivating the developing agents."

Now,

1. Pyrocat-HD type developers are high pH developers as they use Carbonate as the alkali.

2. Acid stop bath is not advised by the inventors and manufacturers of Pyrocat-HD type developers as they fear it will affect the stain. There are also reports of pinholes forming when an acid stop is used with Pyrocat-HD type developers that use Carbonate as the alkali.

3. Going by Haist, water stop bath might not be ideal for Pyrocat-HD type developers. Further, water is poorly buffered and hence pH change due to water stop is likely to be non-uniform and unpredictable. So this could potentially result in non-uniform stain. However, in practice, several practitioners who do use water stop with such developers seem to notice no image nonuniformity.

4. If users of Pyrocat-HD type developers don't want to use either water stop or acid stop for the fears of image non-uniformity, stain degradation, and pinholes, alkaline stop bath is the only alternative.

5. Peter Hogan's alkaline stop bath, reintroduced by John Finch of Pictorial Planet, is targeted for such people - those users of Pyrocat-HD type developers who fear water and acid stops will degrade image quality of their stained negatives.

Although Pyrocat is a highly alkaline developer it is far from being a "highly energetic buffered developer." It is really quite dilute and with the fairly long development times I have found no image nonuniformity after a water rinse after development instead of an acid stop. I'm not against acid stop baths: I use one all the time for fibre paper.

albada · Sep 21, 2022

Raghu Kuvempunagar said:
This is what Haist (Vol 1, Chapter 12, page 540-541, says about water stop baths:

However, image nonuniformity may result from the use of a water stop bath following development in a highly energetic buffered developer of high pH. An acidic stop bath is required in this case because development is stopped more quickly by the neutralization of alkali of the remaining developer, inactivating the developing agents."

I disagree with Haist. With a fast developer, I suspect a water bath will be more uniform than an acid stop. Suppose you're pouring stop into the tank. Your pour-rate won't be consistent, and you will be moving the tank a little (if it's at an angle to increase pour-rate), which will cause the liquid-level to sometimes stop rising momentarily during the pour-in. In that time, you could get a line on the negative because the neg below liquid has stopped but above it hasn't yet stopped. But with a slow-acting water-stop, such a pause in liquid-rise will have less effect, resulting in greater evenness. Thus, a water-stop is more tolerant of uneven pour-rate.
Do you want to bother testing this theory of mine? Me neither.

Ian Grant · Sep 21, 2022

Raghu Kuvempunagar said:
This is what Haist (Vol 1, Chapter 12, page 540-541, says about water stop baths:

"Image formation may be brought slowly to a stop by immersing the photographic material in water. Water stop baths of 30 to 60 sec duration have often been recommended, especially following a fine-grain or high-definition developer of low alkalinity. In this case the water bath acts as the second bath of a two-bath developer. However, image nonuniformity may result from the use of a water stop bath following development in a highly energetic buffered developer of high pH. An acidic stop bath is required in this case because development is stopped more quickly by the neutralization of alkali of the remaining developer, inactivating the developing agents."

Now,

1. Pyrocat-HD type developers are high pH developers as they use Carbonate as the alkali.

2. Acid stop bath is not advised by the inventors and manufacturers of Pyrocat-HD type developers as they fear it will affect the stain. There are also reports of pinholes forming when an acid stop is used with Pyrocat-HD type developers that use Carbonate as the alkali.

3. Going by Haist, water stop bath might not be ideal for Pyrocat-HD type developers. Further, water is poorly buffered and hence pH change due to water stop is likely to be non-uniform and unpredictable. So this could potentially result in non-uniform stain. However, in practice, several practitioners who do use water stop with such developers seem to notice no image nonuniformity.

4. If users of Pyrocat-HD type developers don't want to use either water stop or acid stop for the fears of image non-uniformity, stain degradation, and pinholes, alkaline stop bath is the only alternative.

5. Peter Hogan's alkaline stop bath, reintroduced by John Finch of Pictorial Planet, is targeted for such people - those users of Pyrocat-HD type developers who fear water and acid stops will degrade image quality of their stained negatives.

Actually acid stop baths are recommended for use with Pyrocat HD, but at half the normal strength. The supposed issue is out gassing of CO2 from Carbonate absorbed in the emulsion as it's neutralised by the acid. This was an issue with older softer emulsions and the more concentrated old Pyro developers.

Having used Pyrocat HD for 17 or 18 years now I've never had an issue using an acid stop bath, and for most of the time a water stop, that's in formats up to 10x8. It would be the same with any similar developer using Pyrocatechin.

The use of an Alkali fixer or an Alkali Stop Bath is due to the myth that an Acid Fixer, or Stop Bath, degrades and removes some of the staining effects. That brings us to PE - Ron Mowrey's observations when formulating and testing Alkali Fixers, now he wasn't using Staining Developers, he observed Dichroic fogging occurring when an Acid Stop Bath wasn't used before an Alkali Fixer. This is because the developer isn't neutralised, and some development continues in the initial stages of fixing. So Ron actually recommended using an Acid Fixer before using an Alkali Fixer. There are no issues using a Water Stop followed by an Acid Fixer.

Now with a staining developer and a Water Stop or Alkali Stop any Dichroic fogging from an Alkali Fixer will be close in colour to the staining created during development, and could lead to uneven results.

Ian

Anon Ymous · Sep 21, 2022

albada said:
I disagree with Haist. With a fast developer, I suspect a water bath will be more uniform than an acid stop. Suppose you're pouring stop into the tank. Your pour-rate won't be consistent, and you will be moving the tank a little (if it's at an angle to increase pour-rate), which will cause the liquid-level to sometimes stop rising momentarily during the pour-in. In that time, you could get a line on the negative because the neg below liquid has stopped but above it hasn't yet stopped. But with a slow-acting water-stop, such a pause in liquid-rise will have less effect, resulting in greater evenness. Thus, a water-stop is more tolerant of uneven pour-rate.
Do you want to bother testing this theory of mine? Me neither.

There were several cases where someone used a water rinse after C41 developer and got seriously uneven development. Using C41 bleach, which is quite acidic, or a stop bath prevents this. And C41 developer is the definition of fast developer at 3:15...

Ian Grant · Sep 21, 2022

albada said:
I disagree with Haist. With a fast developer, I suspect a water bath will be more uniform than an acid stop. Suppose you're pouring stop into the tank. Your pour-rate won't be consistent, and you will be moving the tank a little (if it's at an angle to increase pour-rate), which will cause the liquid-level to sometimes stop rising momentarily during the pour-in. In that time, you could get a line on the negative because the neg below liquid has stopped but above it hasn't yet stopped. But with a slow-acting water-stop, such a pause in liquid-rise will have less effect, resulting in greater evenness. Thus, a water-stop is more tolerant of uneven pour-rate.
Do you want to bother testing this theory of mine? Me neither.

Fast development isn't (usually) done in developing tanks, for the reasons you mention, usually it would be tray processing, or machine. When I tray processed 10x8 films it was quick to tip the developer out of the tray and pour in the stop bath, the film would be completely covered in stop bath in seconds.

An exception is C41 which is a relatively fast development time.

Going back to the use of stop baths and older soft emulsions where almost all developers were quite concentrated and containing Carbonate, it's interesting that some of my boxes of pre WWII Illingwarth glass plates give recommended developer formulae and fixer, and make no reference to stop baths. In fact they say after rinsing then fix in the following. Looking in 5 early Ilford Manual of Photography books 1890s up to 1946, there's no mention of use of a stop bath, it's the same in some other books. Kodak Ltd's 1940 Professional Catalogue does not list Stop Bath.

In his book "Developing" 1st edition 1940 Curt Jacobson states that occasionally a stop bath can be used, LP Clerc Photography Theory and Practice 1937 indicates that there can be issues with Carbonates and Stop Baths. He recommends a weak Metabisulpite solution or a tanning stop bath - an acidified Potassium Alum solution. The Gevaert Manual of Photography 1938 only suggests a stop bath for prints.

So it appears stop bathe were rarely used in the past.

Ian

miha · Sep 21, 2022

Ian Grant said:
So it appears stop bathe were rarely used in the past.

Another testament to the above:

Source: https://www.photomemorabilia.co.uk/Ilford/Chronology - Intro.html

Okay, how does alkaline stop bath actually work?

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