How Developer PH affects film base plus fog, illustrated

If open gate is 0.3 then your results look good. If you fix some Fomapan 100 with no development, and read it do you get between 0.20 and 0.25 base?

Often 35mm film base has about that much gray tint to help with anti-halation. (Some film specifically doesn’t, and that film is suitable for reversal processing to make black and white slides).

The curve shapes are fairly similar with fog being the chief difference.

This is starting to look like you are getting down to a real good minimal base +fog by reducing pH with not much impact on speed.

What are the horizontal steps? Whole stops? If so maybe you are losing a stop of speed

Bill Burk said:

What are the horizontal steps? Whole stops? If so maybe you are losing a stop of speed

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Horizontal is whole stops, and yep, there's an extra step in the higher ph version before it really plateaus out to fog, given the higher contrast, I'm not surprised. I just exposed and processed 3:15 and 5:30, and they're hanging up to dry, so either late today or tomorrow some time I'll have two to show. I'd expect the speed difference to shrink quite a bit between the two as we get to zone contrast.

Here's the latest with 3:15 and 5:30 at pH 11.5 and 10.5 respectively. The extra 30 seconds at 10.5 really jacks up the contrast, the lower time at 3:15 really lowers the fog, but not really the contrast. This is the nature of ascorbic acid on Fomapan films, they are very sensitive to it. 5:15 at pH 10.5 is probably a nice middle ground, though I might throw in the 4 grams of iodized salt to see what that looks like.

I added an extra stop on the top end, so the range is +2 to -9 EV in full stops, the 0 point is a correctly exposed gray card at EI 100.



I subtracted the open gate reading, and redacted the labels for the 5:00 pH as there is some overlap.

Interestingly, lower pH does actually lower the fog floor and allow higher gamma through more development time, at least with Fomapan and Rodinal/Ascorbate based developers.

My impression is, that the fog to contrast ratio over time is very dependent on the exact developer composition, and that David has mostly looked at very different developers in the past.

Some credible scientific article claims, that assuming sane compositions and correct development, developers will reach optimal results (speed/grain/sharpness), if they are given ten or more minutes to do their job. That green line in your graph looks like you get much better film speed simply because the film has at least 5:30 to develop.

Rudeofus said:

That green line in your graph looks like you get much better film speed simply because the film has at least 5:30 to develop.

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The funny thing with Fomapan and ascorbic acid/ascorbate is there seems to be a threshold time where the development and density really takes off once you hit the threshold time. That time seems to be pH dependent, as the high pH didn't change contrast much from 4:00 to 3:15, whereas, the low pH seemed to be less than the threshold time at 5:00, but 5:30 was just enough to really get the density going, and the contrast is very close to the higher pH contrast, BUT, with considerably lower fog.

I'd prefer a development time in the 7:30-10:00 minute range, so I'll ever so slightly start to lower the pH and also add the iodized salt (which will lower the pH due to the baking soda filler content). If you figure film base plus fog to be ~0.27, that puts ~+0.1 at the 0.367507 mark on the green line, which puts +4 stops at the 0.974901 mark, which is 0.704901 above fb+f, which works out to ~EI 50. Over the next day or two I'll add the salt after adding the borax to get to pH 10.5, note the new pH and do a run at 6:15, and 7:30.

Does anybody know at what pH Rodinal effectively turns off and stops developing? I want to be low enough to slow it down, but also high enough to activate the ascorbate.

Development threshold for p-Aminophenol, which is the driving force behind Rodinal, is 9.35 according to Haist. The ascorbate in your developer will work as secondary development agent to the p-Aminophenol, so the latter will effectively determine whether development happens or not.

Unless you want to absolutely stick to iodized table salt as ingredient, you might want to think about using separate chems to get the effect you want. With your current attempt you lower pH (bicarbonate), add restrainer (iodide) and add a restrainer which turns into a silver solvent at higher concentrations (chloride).

Rudeofus said:

Unless you want to absolutely stick to iodized table salt as ingredient, you might want to think about using separate chems to get the effect you want. With your current attempt you lower pH (bicarbonate), add restrainer (iodide) and add a restrainer which turns into a silver solvent at higher concentrations (chloride).

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Part of this experiment was to see whether I could get a reasonably good developer using chemistry that I could buy locally from my grocery/hardware store. I bought everything except the lye (sodium hydroxide) from the same place I buy my groceries. The lye came from the home improvement store next door to my lab, so in that respect, I’m at least partially successful. I imagine the added iodized salt will slow it down a bit, and if I need lower pH, it’ll just mean more borax.

I don’t really have a problem with getting the raw pure ingredients per se, I just wanted to see if I could get reasonably good results with an easy to obtain list of things that was also somewhat unique. I know Gainer did a lot of experimentation before, but I don’t recall seeing anything listed anywhere with no sulphite at all and iodized salt. I’m sure someone somewhere has done this at some point, but I’ve not seen it.

I forgot that you exaggerate the vertical axis so I didn’t comment earlier. Your contrasts are not what I would call high. The green curve is closest to a ‘Normal’ pictorial contrast. (0.62 CI would be approximately ASA parameters but it’s good to develop pictures a bit less like to 0.55 CI).

Here’s a rough approximation of your contrast index. I didn’t use precise math or graphs, so if you try to calculate you might get a little different....
Blue 0.50 CI
Yellow 0.46 CI
Green 0.54 CI
Red 0.25 CI

Bill Burk said:

I forgot that you exaggerate the vertical axis so I didn’t comment earlier. Your contrasts are not what I would call high. The green curve is closest to a ‘Normal’ pictorial contrast. (0.62 CI would be approximately ASA parameters but it’s good to develop pictures a bit less like to 0.55 CI).

Here’s a rough approximation of your contrast index. I didn’t use precise math or graphs, so if you try to calculate you might get a little different....
Blue 0.50 CI
Yellow 0.46 CI
Green 0.54 CI
Red 0.25 CI

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I agree that the green line is the most desirable out of the 4. I might be able to pick up a small amount of shadow speed by adding just enough solvent to expose more latent image centers via the addition of sodium chloride. Per @Rudeofus it can act as a solvent if there’s enough of it there.