a few questions about restrainers for film

greg zinselmeier · Jan 2, 2022

Hello,
A. thank you in advanced for contributing to this post, But can we limit discussion to "only" effects on Film (not paper)? thank you

1. I am only aware of two restrainers. Potassium Bromide and Benzotrizole. Others?

Reading the Darkroom CookBook I understand one should use about 1/10 the weight of KBr when using BZT as a substitute. Do others concur?

If there is reading material any of you APUGER's are aware of that gives more in depth coverage on this topic? Can you please suggest to me those books, research paper's, websites, etc. . . . .thank you

2. I also read that if added in larger quantities, than needed to eliminate or reduce Dichrotic fog, the restrainer inhibits developement of exposed halides to an extent. Is that true? if so, Is that "restraining action" evenly proportional? or does the restariner retard more highlight values or more shadow values? that is. .. IF ADDED TOO MUCH.So would that result in loss of speed? or less or more contrasterrrrrr negative?

3. If action taken was . . . . to keep adding restrainer to the developer test after test? would it just keep taking longer(time) to get the same values, as with the previous test? Or would "no development" ever happen? or what effect on the curve does the additonal restrainer have?

I appreciate your response
best regards
Greg Z.

Rudeofus · Jan 4, 2022

@ 1) There are many well known restrainers, which can be grouped into two main classes:

Inorganic restrainers, typically halides like bromides and iodides. These compounds shift the development reaction to the right and thereby increase the required developer activity level to develop silver halide grains.
Organic restrainers. These are organic molecules, which form poorly soluble silver salts and thereby inhibit the development reaction. Like inorganic restrainers they increase the required developer activity level to develop silver halide grains. Common examples of such restrainers are Benzotriazole, Nitro-Benzimidazole or Phenyl-Mercaptotetrazole, but many are known in photographic literature. Their most important property is the solubility product of their respective silver salts - stronger restrainers form the more insoluble silver salt.

One important difference between different restrainers is also to which extent they get used up during development. Those restrainers forming more insoluble silver salts will replace the bromide anion in silver bromide emulsions and thereby get used up. This is especially relevant if one reuses developers. Color developers are designed such, that the bromide and iodide released during development together with the replenishment regime keeps the concentration of bromide and iodide unchanged between dev runs.

There are in depth descriptions of different restrainers in common photographic literature, some of which is freely available due to expiration of copyright.

@ 2)
If you look at an exposed emulsion, you need different levels of energy to develop different silver halide grains:

The highest amount of energy is needed to develop unexposed grains. The result would be fog.
Then there are weakly exposed grains. If they get developed, you get shadow detail. If film is very fogged from old age or poor storage, some of the unexposed grains are easier to develop than weakly exposed ones, this is where aged film loses speed, since you can no longer differentiate between weakly exposed and unexposed grains.
Strongly exposed grains need comparatively little energy to get developed.

If restrainers raise the energy required to develop grains, and if the rest of the developer doesn't change, then increasing amounts of restrainer will at first eliminate fog, then eventually lower film speed, until it finally prevents development altogether. As you add restrainer and transition from stage 2 to 3, you lower film speed to the point, where you get increased contrast, so you will typically find lots of restrainer in high contrast developers.

Note, that some of these restrainers not only form poorly soluble silver salts, but at high concentrations form soluble complexes with silver. There are fixers based on concentrated solution of Ammonium Iodide! Therefore you have to be careful when adding excessive amounts of restrainer, at some point they will act as solvent which will increase developer activity.

@ 3)
As mentioned previously, as you add restrainer you at first eliminate fog, then you reduce film speed and increase contrast, then you eventually suppress development, and with many restrainers further increase will actually reignite the developer. Not every organic restrainer does this, and not ever restrainer is water soluble in amounts necessary to form these complexes.

If one wants to reduce contrast with restrainers, one can not just add it to the developer. Special restrainer release techniques are necessary to trigger release of restrainer in strongly developed areas. This will both increase sharpness through adjacency effects and reduce contrast:

High iodide emulsions such as Delta 3200 release enough iodide during development that contrast is lowered and stronger pushes are possible without runaway contrast.
Color negative film releases strong restrainers when special couplers get in contact with oxidized developer. Instead of forming dyes, these DIR couplers release compounds like Phenyl-Mercaptotetrazole to severely restrict development in these regions. This is what gives Ilford's XP2 its huge latitude and sharpness together with fine grain.

Fully acknowledging your request to limit this discussion to film, I still encourage you to do at least initial tests with othochromatic paper, since you can observe developer activity during the process in red light. You will save yourself from endless waste of material, if you get the hang of these restrainers before you start fine tuning film developers.

greg zinselmeier · Jan 5, 2022

I reaally appreciate the time you spent on this!!!! ( response) thank you ! . this is very helpfull. I will take up your suggestion and make a paper developer without a restrainer and then add "amount" after each new print developed. to see how effects progress.

greg zinselmeier · Jan 5, 2022

oh, another question, what about Potassium Iodide as a restrainer?

Alan Johnson · Jan 5, 2022

Not sure if it is relevant to your project but I ran a test with expired film:
https://www.photrio.com/forum/threads/1-benzotriazole-expired-film.120922/
I believe BZT is preferred for higher pH developers , pH>9 and potassium bromide for lower pH, IDK why.

DREW WILEY · Jan 5, 2022

Yes - that's how I factor it. 1/10th as much benzotriazole gram-wise as the called for KBr amount. But the net effect is slightly different. Frankly, I don't even use a supplementary restrainer in film dev formulas unless I specially need a "toe cutter" effect, and that is only with respect to technical lab tweaks like unsharp mask development, and not general photography. And of course, addition of a restrainer lowers the effective film speed. The only other application I can think of is for reducing overall fog in outdated film.

greg zinselmeier · Jan 5, 2022

Thanks to everyone who responded. Your thoughts and suggestions were well received.

Rudeofus · Jan 6, 2022

greg zinselmeier said:
oh, another question, what about Potassium Iodide as a restrainer?

Potassium Iodide is a very powerful restrainer, therefore it is not commonly used in B&W developers. It is very common in color developers, first because of the reason described in my previous posting, second, because it allows to set the color balance. As you know, color film needs at least three layers to create three independent color channels, and the iodide will mostly interact with the top most layer. A carefully balanced combination of iodide and bromide allows you to emphasize development of lower emulsion layers, while the iodide restrains development of the top most layer.

Ron also suggested another reason to add iodide to a B&W developer: restrainer action is not linear, but has a threshold. As film develops, additional iodide is released from the grains. The base level of iodide controls, at which point the preexisting iodide together with the released iodide become active. A carefully crafted combination of iodide and strong solvent can therefore be used to increase sharpness.

John Wiegerink · Jan 6, 2022

Rudeofus said:
Potassium Iodide is a very powerful restrainer, therefore it is not commonly used in B&W developers. It is very common in color developers, first because of the reason described in my previous posting, second, because it allows to set the color balance. As you know, color film needs at least three layers to create three independent color channels, and the iodide will mostly interact with the top most layer. A carefully balanced combination of iodide and bromide allows you to emphasize development of lower emulsion layers, while the iodide restrains development of the top most layer.

Ron also suggested another reason to add iodide to a B&W developer: restrainer action is not linear, but has a threshold. As film develops, additional iodide is released from the grains. The base level of iodide controls, at which point the preexisting iodide together with the released iodide become active. A carefully crafted combination of iodide and strong solvent can therefore be used to increase sharpness.

Rudeofus,
The above comments about adding iodide to a developer to develop film with already incorporated iodide to get increased sharpness puzzled me. Is what you are saying similar to Ilford Perceptol developer and say a 1+2 dilution for a balanced, sharp developer? Perceptol is said to be pretty much just ID11 plus salt (NaCI) added. By diluting Perceptol you cut the sulfite and NaCI, which gives a good balance between fine grain and sharpness, but with slight speed loss. At least that’s my experience anyway and HP5+ in Perceptol 1+2 looks it. I took Chemistry in high school, but the only thing I remember about it was that I took the class. Of course that was getting close to 60yrs ago and there are many things I have forgotten in that time frame. JohnW

Rudeofus · Jan 6, 2022

There are different ways to boost sharpness, and almost all of them basically try to create Mackie lines by restraining development as it happens.

Developer dilution causes local exhaustion near sites of strong development, this is what you get with Perceptol 1+2. Developer dilution also means, that fewer grains near the surface get developed, this is why you trade smoothness for sharpness.

Release of restrainer is a different mechanism with quite similar results. This can happen automatically in high iodide emulsions, or with intentional additions like DIR couplers in color negative film. A special case is the difference between HQ and HQMS: if HQ gets oxidized and sulfonated during development, it is still a developer, whereas oxidized and sulfonated HQMS is not. This makes HQMS yield sharper results.

The restraint through iodide seems to have some threshold value. If your developer starts with no iodide at all, some grains have to be developed until enough iodide is released to effectively restrain further development. If you add iodide to your developer, less development is necessary to cause self restraint. Ron claimed, that earlier onset of restraining action increases sharpness. Since sharpness is the most difficult to evaluate property, especially with our amateur means, this topic never saw much amateur research, unlike grain and speed.

John Wiegerink · Jan 6, 2022

Rudeofus said:
There are different ways to boost sharpness, and almost all of them basically try to create Mackie lines by restraining development as it happens.

Developer dilution causes local exhaustion near sites of strong development, this is what you get with Perceptol 1+2. Developer dilution also means, that fewer grains near the surface get developed, this is why you trade smoothness for sharpness.

Release of restrainer is a different mechanism with quite similar results. This can happen automatically in high iodide emulsions, or with intentional additions like DIR couplers in color negative film. A special case is the difference between HQ and HQMS: if HQ gets oxidized and sulfonated during development, it is still a developer, whereas oxidized and sulfonated HQMS is not. This makes HQMS yield sharper results.

The restraint through iodide seems to have some threshold value. If your developer starts with no iodide at all, some grains have to be developed until enough iodide is released to effectively restrain further development. If you add iodide to your developer, less development is necessary to cause self restraint. Ron claimed, that earlier onset of restraining action increases sharpness. Since sharpness is the most difficult to evaluate property, especially with our amateur means, this topic never saw much amateur research, unlike grain and speed.

Thanks, that helps me understand things a little better. Sometimes we need not know why it works, just that it works. Still, it’s nice to know a little about how something does what it does and why. JohnW

KPA40 · Jan 6, 2022

Rudeofus said:
A special case is the difference between HQ and HQMS: if HQ gets oxidized and sulfonated during development, it is still a developer, whereas oxidized and sulfonated HQMS is not. This makes HQMS yield sharper results.

Does it mean that one could change HQ for HQMS completely or partelary to get a better sharpnes in any b&w developer? That sounds tempting (apart from drastically higher costs) but I don't think it's that simple, is it?

Doremus Scudder · Jan 6, 2022

Rudeofus said:
There are different ways to boost sharpness, and almost all of them basically try to create Mackie lines by restraining development as it happens...

We need to be careful to differentiate between sharpness and acutance here. The former is quite subjective and has a lot to do with micro-contrast. The latter is measured and quantifiable and has to do with accurate rendering of fine detail.

Rudeofus · Jan 6, 2022

KPA40 said:
Does it mean that one could change HQ for HQMS completely or partelary to get a better sharpnes in any b&w developer? That sounds tempting (apart from drastically higher costs) but I don't think it's that simple, is it?

HQMS by itself is much milder than HQ, therefore you need more of the expensive ingredient HQMS in your developer. The cheapest Phenidone+HQMS developer I frequently use for B&W is E-6 first developer diluted 1+9 with tap water. You can even do this with partially used E-6 FD, since there is no requirement for careful color balance any more.

Rudeofus · Jan 6, 2022

Doremus Scudder said:
We need to be careful to differentiate between sharpness and acutance here. The former is quite subjective and has a lot to do with micro-contrast. The latter is measured and quantifiable and has to do with accurate rendering of fine detail.

Wikipedia confirms there is a difference, but it's the other way round: sharpness is real detail resolution, whereas acutance is just the perception of the former with no real gain in detail resolution. Obviously most "sharpness" developers go after acutance, not real sharpness/resolution.

MattKing · Jan 6, 2022

Rudeofus said:
Wikipedia confirms there is a difference, but it's the other way round: sharpness is real detail resolution, whereas acutance is just the perception of the former with no real gain in detail resolution. Obviously most "sharpness" developers go after acutance, not real sharpness/resolution.

Interesting - I understand it to be exactly the reverse.
Acutance is edge contrast, and is objectively measurable.
Acutance is the major contributor to the almost entirely subjective phenomena referred to as "sharpness".
The other contributors being overall contrast and resolution.

DREW WILEY · Jan 6, 2022

MTF is diagnostic, and supposedly related to standardized lens testing methods. Nowadays, its basically become etherial pixel-peeper trash talk. At the moment, my computer security classifies Wickedpedia as virus-like, and won't let me in at all, but there are always better sources of information. I use my own eyes. Edge effect and PERCEIVED SHARPNESS go together, but not alway in tandem with hypothetical sharpness. A lot depends on the SPECIFIC film developer combination, as well as the degree of magnification in print. Every snowflake becomes something else at a different temperature or weight load. All I care about is the end result. Film chemists can figure out the rest, and web surfers can continue to float downriver into their own little make-believe world, if they wish, filled with pixels and pixies.

Rudeofus · Jan 6, 2022

I believe, that this discussion started, when I described certain restrainers or developers as "increase sharpness". I did not write that wikipedia article, but claim with conviction, that its articles are usually well founded and researched. Please let this discussion not devolve into yet another sharpness/acutance debate.

DREW WILEY · Jan 6, 2022

Back on track regarding both conversations : I would think in general that restrainers are the wrong way to go if you want to increase acutance. In most cases, more crystal growth enhances it, yet perhaps at the expense of greater graininess. I have specific personal developer tweaks of that theory for sake of certain films like TMax 100 which deliver tremendous detail, yet have relatively poor edge acutance, so end up look less sharp and not more unless specifically developed to enhance the edges. Going to opposite direction, I do use a restrainer for unsharp TMax masks, to not only keep the bottom of the toe straighter, but deliver overall grain reduction at the same time, more softly. Certainly not all films are the same in this respect, but this is one valid example.

greg zinselmeier · Jan 6, 2022

hello,

does anybody have any books they could recommend that explains well restrainers used film developers. Moreover the relationship between ( restrainers and) time,temp,aggitation technique, PH, which base to use, the amount of developing agent, and othe things I do not know about? I am just trying to get to control the MACRO contrast oi "a developer /film combo" !!!!, all of these "other things" like micro contrast, speed, acutance, and sharpness I will deal with later on.

thank you to all who have posted.

DREW WILEY · Jan 7, 2022

"Macro contrast" implies overall contrast, and any supplementary restrainer is going to somewhat curtail the curve shape and length, especially at the bottom end shadow-reproduction-wise. As far as general film chemistry textbooks go, sure, they're out there; but I can't think of any which specifically involve current films - they're all old. Even grain structure engineering has largely changed in the interim.

greg zinselmeier · Jan 7, 2022

thanks Drew, for the update.

I will say this, that I have done tests with no restrainer added, and restrainer added for the same time, And the results were that the shoulder was NOT as dense, and the toe was not as dense, but not as much, as the difference as on top, so to speak. It seems that when I add a restrainer that the toe is somewhat changed, but the shoulder is decapitated quickly? maybe I should send the results in. would anyone be interested in my mythod and correcting the "royal ear" as it were. actually the "royal chemical mind" ? I would love some help, testing on film how restrainers work on film .

greg zinselmeier · Jan 7, 2022

Moreover, . .. .. HOW DO YOU TEST FOR RESTRAINER?

relistan · Jan 8, 2022

Rudeofus said:
@ 1) There are many well known restrainers, which can be grouped into two main classes:

Inorganic restrainers, typically halides like bromides and iodides. These compounds shift the development reaction to the right and thereby increase the required developer activity level to develop silver halide grains.

Organic restrainers. These are organic molecules, which form poorly soluble silver salts and thereby inhibit the development reaction. Like inorganic restrainers they increase the required developer activity level to develop silver halide grains. Common examples of such restrainers are Benzotriazole, Nitro-Benzimidazole or Phenyl-Mercaptotetrazole, but many are known in photographic literature. Their most important property is the solubility product of their respective silver salts - stronger restrainers form the more insoluble silver salt.

One important difference between different restrainers is also to which extent they get used up during development. Those restrainers forming more insoluble silver salts will replace the bromide anion in silver bromide emulsions and thereby get used up. This is especially relevant if one reuses developers. Color developers are designed such, that the bromide and iodide released during development together with the replenishment regime keeps the concentration of bromide and iodide unchanged between dev runs.

There are in depth descriptions of different restrainers in common photographic literature, some of which is freely available due to expiration of copyright.

@ 2)
If you look at an exposed emulsion, you need different levels of energy to develop different silver halide grains:

The highest amount of energy is needed to develop unexposed grains. The result would be fog.

Then there are weakly exposed grains. If they get developed, you get shadow detail. If film is very fogged from old age or poor storage, some of the unexposed grains are easier to develop than weakly exposed ones, this is where aged film loses speed, since you can no longer differentiate between weakly exposed and unexposed grains.

Strongly exposed grains need comparatively little energy to get developed.

If restrainers raise the energy required to develop grains, and if the rest of the developer doesn't change, then increasing amounts of restrainer will at first eliminate fog, then eventually lower film speed, until it finally prevents development altogether. As you add restrainer and transition from stage 2 to 3, you lower film speed to the point, where you get increased contrast, so you will typically find lots of restrainer in high contrast developers.

Note, that some of these restrainers not only form poorly soluble silver salts, but at high concentrations form soluble complexes with silver. There are fixers based on concentrated solution of Ammonium Iodide! Therefore you have to be careful when adding excessive amounts of restrainer, at some point they will act as solvent which will increase developer activity.

@ 3)
As mentioned previously, as you add restrainer you at first eliminate fog, then you reduce film speed and increase contrast, then you eventually suppress development, and with many restrainers further increase will actually reignite the developer. Not every organic restrainer does this, and not ever restrainer is water soluble in amounts necessary to form these complexes.

If one wants to reduce contrast with restrainers, one can not just add it to the developer. Special restrainer release techniques are necessary to trigger release of restrainer in strongly developed areas. This will both increase sharpness through adjacency effects and reduce contrast:

High iodide emulsions such as Delta 3200 release enough iodide during development that contrast is lowered and stronger pushes are possible without runaway contrast.

Color negative film releases strong restrainers when special couplers get in contact with oxidized developer. Instead of forming dyes, these DIR couplers release compounds like Phenyl-Mercaptotetrazole to severely restrict development in these regions. This is what gives Ilford's XP2 its huge latitude and sharpness together with fine grain.

Fully acknowledging your request to limit this discussion to film, I still encourage you to do at least initial tests with othochromatic paper, since you can observe developer activity during the process in red light. You will save yourself from endless waste of material, if you get the hang of these restrainers before you start fine tuning film developers.

Super helpful post, thanks!

DREW WILEY · Jan 9, 2022

greg - the toe, which is by very definition was less dense in developed film, is naturally going to be affected considerably more by a restrainer than the highlights. With paper, the effect if just the opposite, and the restrainer cuts back the relatively minimal highlight and fog density. Pretty simple. That's why it basically operates as a toe-cutter when added to film developers, and a highlight clearing tool when added to paper developers. A restrainer restrains or holds back development,
so will have the strongest effect where development of density is the weakest to begin with,

Objective testing is done just like any other end-result film test - with densitometer curve plotting, with versus without the developer alteration.

a few questions about restrainers for film

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