How Developer PH affects film base plus fog, illustrated

[Adrian Bacon]

I've recently been experimenting with an experimental black and white film developer that is based off of Patrick Gainer's Rodinal/Ascorbate experiments and have seen a fair amount of postings around the internet about how the developer PH affects how much film base plus fog you'll get with some developer combinations, but not really a visual demonstration posted anywhere. So.... While I was working out an ideal working solution PH for my developer, I thought I'd share what the PH does to the film base plus fog visually speaking. Many old timers probably already know this, but it's useful for the newer/younger guys, or hobbyist home brewers.

Image 1 is the open film scanner gate with no film. It's black. It should be, and is the black reference for the following frames.

Image 2 is Fomapan 100 processed for 5 minutes at 24C and rotary agitation using the Rodinal/Ascorbate based developer with the working solution PH at ~11.5. The total working solution was 612ml (12ml concentrate, 600ml water). The scanner settings were kept exactly the same, so this is where the film base plus fog is relative to the open gate with no film in it at all.

Image 3 is the same film and processing parameters as Image 2 except: The working solution PH was pulled down to ~10.5. The film base plus fog is higher than the open gate, but it's close enough that I still get a nice strong black. The grain is also reduced quite a lot compared to Image 2.

Image 4 is the same film and processing parameters as Image 3 except: I added 4 grams of iodized salt. The iodized salt contains 67mcg per serving size and each serving size is 1.5 grams, so it has a total of ~178mcg of iodide in the 612ml of solution, plus the salt and sodium bicarbonate filler taking up the rest of the 4 grams. I added the salt before adjusting the PH, so the sodium bicarbonate in the salt didn't effect the final PH of the working solution. The film base plus fog level didn't really change from Image 3, but, the grain is dramatically smaller and tighter than Image 3. This isn't really PH related, but I thought I'd include it because it's interesting. The salt and/or iodide results in much finer grain.

I also did a run where the working solution PH was 9 and ended up with barely there images. I didn't bother including that here as the film base fog didn't appreciably change from image 3 and 4.

So there you have it. This will vary with what developer you're using/mixing up, but for those of us that are mixing our own, it pays to pay attention to the PH of our working solution, and get the PH so that it's just high enough to get things going, but not so high that we get more fog and grain that we want/need.

 

[AgX]

Especially for newcomers I consider a reversed tonality better to understand, open gate depicted as max. transmission, thus max . brightness.

 

[Adrian Bacon]

Especially for newcomers I consider a reversed tonality better to understand, open gate depicted as max. transmission, thus max . brightness.

Possibly, however, in Adobe Lightroom (this is what you’re seeing here), the highlights are completely smashed, meaning 3+ stops of exposure are jammed into the top 10% of the luminance range, so if I show it as a positive scan, it’s actually relatively hard to see the difference unless I introduce a tone curve to pull things down or pull the exposure way down so max transmission is closer to middle grey. At that point, since this is negative film, you might as well show it as it would look in a print.

 

[Anon Ymous]

Ideally, a density reading of film base plus fog would be better than anything else. Can be easily done if you have Vuescan.

 

[Bill Burk]

Nice topic for discussion!

Did you note the pH of the first developer which gave you a small amount of fog?

Did you check to see if you lost speed with the lower pH?

 

[Adrian Bacon]

For those that prefer to look at log unit values. Transmission density readings.

 

[Adrian Bacon]

Nice topic for discussion!

Did you note the pH of the first developer which gave you a small amount of fog?

Did you check to see if you lost speed with the lower pH?

Image 1 was the open scanner gate with no film in it, so there's no pH, it just represents maximum transmission density to provide some density context to the other images. Image 2 was ~11.5, Images 3 and 4 were both ~10.5 pH.

I've not yet checked for speed differences or worked out a development time to get roughly zone system contrast. Those are next on the list.

 

[Rudeofus]

If you scan an open frame, density should be very close to 0.00, not some number > 3 .... also frames with some b+f should have higher densities, not lower ones.

 

[Adrian Bacon]

If you scan an open frame, density should be very close to 0.00, not some number > 3 .... also frames with some b+f should have higher densities, not lower ones.

It's positive transmission density before you invert it. If you want to invert it, then, relative to Log 4.0 (which once inverted would be Log 0.0), Image 1 would be Log 0.087, Image 2 would be Log 1.025, Image 3 would be Log 0.368, and Image 4 would be 0.363.

 

[David Lyga]

I fail to see the relevance. You have demonstrated 'fog' but did NOT demonstrate FOG IN RELATION TO THE IMAGE. Thus, there is no real comparison here. If a higher pH does deliver excess fog (common sense says that it does because you ARE developing 'more'), what about the general contrast of the image?

In other words, whether one develops film for a much longer time in a low pH developer, or whether one develops film for a much shorter time in a high pH developer, one could very well end up with identical gamma (contrast index) with fog levels being, also, identical. I fail to see what has been proven. Maybe someone can enlighten me.

Bottom line: I have found that pH does NOT affect fog levels when the contrast level of the IMAGE must remain the same. Fog restrainers DO, like benzotriazole, especially in conjunction with excess hydroquinone (because the HQ forces more contrast out of the film and this excess contrast acts, in a relative sense, to reduce threshold density).. - David Lyga

 

[Adrian Bacon]

I fail to see the relevance. You have demonstrated 'fog' but did NOT demonstrate FOG IN RELATION TO THE IMAGE. Thus, there is no real comparison here. If a higher pH does deliver excess fog (common sense says that it does because you ARE developing 'more'), what about the general contrast of the image?

In other words, whether one develops film for a much longer time in a low pH developer, or whether one develops film for a much shorter time in a high pH developer, one could very well end up with identical gamma (contrast index) with fog levels being, also, identical. I fail to see what has been proven. Maybe someone can enlighten me.

Bottom line: I have found that pH does NOT affect fog levels when the contrast level of the IMAGE must remain the same. Fog restrainers DO, like benzotriazole, especially in conjunction with excess hydroquinone (because the HQ forces more contrast out of the film and this excess contrast acts, in a relative sense, to reduce threshold density).. - David Lyga

Ermmm... not trying to prove anything, merely showing that everything else being equal except the pH, the fog level can vary quite a lot.

As I said in the first post, this is probably obvious to the older timers, but probably not likely to the newer folks.

 

[David Lyga]

OK, I am with you, Adrian, it is just that the more you develop the more the fog is there. The fog would be just as great if you had a low pH and developed to the same gamma. - David Lyga

 

[Adrian Bacon]

OK, I am with you, Adrian, it is just that the more you develop the more the fog is there. The fog would be just as great if you had a low pH and developed to the same gamma. - David Lyga

Well, the next step will be to work out development times at pH 11.5 and 10.5 to produce the same zone system contrast, so we’ll see what that looks like. I can say with Fomapan 100, for what I’ve run so far, it’s not going to be a significant time difference between the two. The pH 10.5 run I did still had excellent contrast in the images, so I’m not entirely sure that what you’re saying can be applied as a blanket statement to every film and developer combination.

 

[Rudeofus]

OK, I am with you, Adrian, it is just that the more you develop the more the fog is there. The fog would be just as great if you had a low pH and developed to the same gamma.

With the right developer formulations you can get both high contrast and low fog (think D-82), and low contrast with high fog (think POTA). Yes, most developers build up fog as they increase contrast, but the ratio contrast/fog is not constant.

 

[David Lyga]

Yes, there are exceptions, as phenidone does deliver more fog than it has a right to! But ... my angst stemmed from the inferred assertion that sodium carbonate, in and of itself, was worse for fog.

WITH THE SAME DEVELOPER it is NOT a fog determinant. Amount of development is, not the carbonate. You would get the same fog if you had developed for a longer time, in order to achieve the same gamma. I should have specified this qualification (i.e., having to use the same developer) for this statement. In other words, I stand by this: "Given the same developer, with ONLY the level of alkalinity being varied, the fog level stays the same if the same gamma has been achieved".

The literature is filled with stating that "carbonate adds to the fog", but handily does not state that with the increased fog will also come increased gamma levels. That convenient omission has been my bête noire for many decades and I wanted to state this correctly. - David Lyga

 

[Bill Burk]

David, you’re knowledgeable about developing old film with old exposures aren’t you? I know Adrian’s next steps are to check ‘gamma’ (and speed), which simply dropping pH might impact, but I expect there is a formula that restrains fog while still developing a usable image.

There are good formulas for that aren’t there? I assume they would have lower pH than usual, but I don’t know ‘chemistry’ - I am a cookbook type person.

 

[Adrian Bacon]

David, you’re knowledgeable about developing old film with old exposures aren’t you? I know Adrian’s next steps are to check ‘gamma’ (and speed), which simply dropping pH might impact, but I expect there is a formula that restrains fog while still developing a usable image.

There are good formulas for that aren’t there? I assume they would have lower pH than usual, but I don’t know ‘chemistry’ - I am a cookbook type person.

For reference, the formula I’m testing with is:

Per 12ml of concentrate: 600mg of acetaminophen (Tylenol), 3 grams of Ascorbic Acid, add Sodium Hydroxide until pH is 12, let sit for minimum 72 hours.

The working solution is 12ml of concentrate, 600ml of distilled water. PH comes out to ~11.5, to lower the pH, add borax until it’s what you want.

The sodium hydroxide does 3 things, converts the Tylenol into Rodinal, converts the ascorbic acid into sodium ascorbate, and boosts the pH. The ascorbic acid also does multiple things, it’s super additive with the Rodinal, it also develops film, and (in theory) it’s also a preservative, negating the need for sodium sulphite.

You can easily mix up 120ml of concentrate at a time with 12 crushed 500mg Tylenol tablets, 30mg of ascorbic acid, and then add sodium hydroxide 5mg at a time until the ph is 12. It will dissolve the tablets and turn tan and have the consistency of runny honey. Let sit for 72 hours before using.

 

[David Lyga]

David, you’re knowledgeable about developing old film with old exposures aren’t you? I know Adrian’s next steps are to check ‘gamma’ (and speed), which simply dropping pH might impact, but I expect there is a formula that restrains fog while still developing a usable image.

There are good formulas for that aren’t there? I assume they would have lower pH than usual, but I don’t know ‘chemistry’ - I am a cookbook type person.

Yes, a 'fog formula' would have to encompass both benzotriazole and extra hydroquinone. The BZ restricts threshold density while the HQ emphasizes tonal distance between the threshold and highlights. - David Lyga

 

[Adrian Bacon]

Yes, a 'fog formula' would have to encompass both benzotriazole and extra hydroquinone. The BZ restricts threshold density while the HQ emphasizes tonal distance between the threshold and highlights. - David Lyga

In theory, potassium iodide would also act as a restrainer, and let you develop longer without appreciably raising fog levels. In the test above, the iodized salt didn’t appreciably lower the fog because it was already pretty low from the lowered pH, but the grain was dramatically finer, so one thing I might look at is what happens when I add the salt to the high pH mix.

 

[Rudeofus]

That table salt does not only contain iodide as restrainer, but mostly chloride, which in larger amounts acts as silver solvent, c.f. Microdol and Microdol-X. I would suggest that this is where the fain grain effect comes from.

 

[Adrian Bacon]

That table salt does not only contain iodide as restrainer, but mostly chloride, which in larger amounts acts as silver solvent, c.f. Microdol and Microdol-X. I would suggest that this is where the fain grain effect comes from.

Per 1.5g serving size, the salt I have contains 590mg of sodium chloride. The rest of the volume is dextrose, sodium bicarbonate, and yellow prussiate of soda in unspecified amounts in addition to the 67mcg of iodide.

 

[Adrian Bacon]

David, you’re knowledgeable about developing old film with old exposures aren’t you? I know Adrian’s next steps are to check ‘gamma’ (and speed), which simply dropping pH might impact, but I expect there is a formula that restrains fog while still developing a usable image.

There are good formulas for that aren’t there? I assume they would have lower pH than usual, but I don’t know ‘chemistry’ - I am a cookbook type person.

Yesterday I exposed two rolls with my standard setup for testing contrast and speed, and processed one at pH 11.5 for 4 minutes, and one at pH 10.5 for 5 minutes. I haven’t measured them yet, so don’t know what the contrast is, but both descend into film base plus fog by the time you hit 5 stops down from middle Gray. I can see 4 stops down, but not 5 stops down, so if there’s a speed difference, it’s probably less than a stop. I think I might have to do another run with a shorter time for the pH 11.5 as the normal middle gray still looks a little heavy, but that just might be the heavy fog messing with me. The 10.5 pH looks like 5-6 minutes is about right. We’ll see once I measure it and make a chart.

 

[Adrian Bacon]

Here's the raw density readings. The scale on the left is log density, the scale on the bottom is relative exposure values. The 0 mark is a correctly exposed gray card at EI 100. The film used is Fomapan 100. I did not normalize the readings so that the film base plus fog is log 0.0 in order to show the fog level differences. The data labels at each point are the raw density readings for each point.

As I suspected, the pH 10.5 needs another ~30 seconds, the pH 11.5 needs to be pulled in, I'll probably try 3:15, as that's the shortest I'm willing to go. Fomapan films tend to be very sensitive to Ascorbate, so 30 second changes usually result in pretty big differences.

The pH 11.5 has a +1 to 0 EV gamma of 0.72, the pH 10.5 +1 to 0 EV gamma is 0.42

 

[Bill Burk]

Adrian, I am confused by densities near 1 and 0.5, have you also not subtracted the open gate reading?

 

[Adrian Bacon]

Adrian, I am confused by densities near 1 and 0.5, have you also not subtracted the open gate reading?

The open gate reading has not been subtracted. 0.0 on the chart is log 4.2 inverted, the open gate reading once inverted is ~0.3 log.