Sulfite in acutance developers

Here are the concentrations of sodium sulfite in the working solutions of some acutance developers:
FX-37 1+3 (Crawley) 15g/L
FX-55 3.7g/L
DS-2 (Suzuki) 20g/L
DS-12 20g/L
Xtol 1+3 22g/L
I have left out FX-1 and FX-2 as I know sulfite removes metol oxidation product in these.
Sulfite is probably not solvent at the concentrations listed,see the Film Developing Cookbook p55.
So I wonder if anyone can offer any comment on what it does, why it is there? Thanks.

It's there to prevent/slow down the oxidation of metol. I'm sure the big guns with backgrounds in chemistry call add a lot more to it than I can.

In "Photographic Processing Chemistry" p121 LFA Mason says to the effect that oxidation products of developing agents which might affect the course of development react with sulfite which eliminates their effect.The amount of sulfite required is usually quite small.
However, Patrick Gainer has mentioned that the product of development in ascorbates is dehydroascorbic acid and "There is nothing in any ordinary developer that will reduce dehydroascorbic acid to ascorbic acid". I take this to mean oxidation products of ascorbate developers are not affected by sulfite and the question remains 'why is the sulfite there?'

The sulfite is there to prevent oxidation, not counteract it. Sulfite is a very efficient oxygen scavenger.

Does it help stabilize pH?

It won't do much for the pH at such low concentrations relative to total alkali. Acutance developers tend to have very high pH, so the sulfite will be totally in the SO3(2-) form, with practically no HSO3(-).

OTOH, the old standby D-76 has 100 grams / liter of Sodium Sulfite.

PE

I did investigate if sulfite had any effect on film speed by mixing up some PC-Glycol with 0,1,3 and 9 grams/L sodium sulfite but the film speeds were exactly the same within 1/6 stop.
I wonder if sulfite has any effect on acutance or tonality?

I can't speak on the effect of sulfite on tonality, but it does have an effect on accutance. The more sulfite, the less sharp the image. D-76 has a goodly amount of sulfite, 100g, and is known as a moderately fine-grain dev. Dilute D-76 to 1+3 and you get a pretty good accutance dev. The cut-off point is 50g/liter.

You may have to reach this same 50g/liter for it to have an effect on film speed, IDK for sure, but it's a reasonable guess.

Alan Johnson said:

I did investigate if sulfite had any effect on film speed by mixing up some PC-Glycol with 0,1,3 and 9 grams/L sodium sulfite but the film speeds were exactly the same within 1/6 stop.
I wonder if sulfite has any effect on acutance or tonality?

Click to expand...

Alan, this range is too narrow to test either the keeping or the solvency effects. A better example would be to test keeping and sharpness/grain at 0, 10, 20, 40 and 80 g/l or some series like that. And, you have to keep the pH constant.

Then, you have to do direct comparisons of identical scenes.

PE

There are many references in the work of Patrick Dignan to adjusting the sulfite level for different films. Crawley in some of his FX formulas makes reference to sulfite level being adjusted for Adox film. Apparently sulfite reacts differently on different size grains or emulsion formulas. Kodak being quite different from the Adox examples. T grain emulsions were supposed to be intollerant of high sulfite levels.

Mr. Dignan and I had a long talk on the phone one day and apparently sulfite's action is more complex than just an oxygen scavenger but he never did get around to a strait answer and unfortunately he isn't around anymore to ask.

High sulfite concentrations do hurt acutance (try D-25 if you doubt that) so low concentrations in acutance formulas make sense, it does make sense that even in small quantities on large crystals it may have a "cracking effect" attacking the crystal to expose the sensitivity spec to the developing agent without true solvent action. If the effect does exist it would be different for every different emulsion and mix of developing agents.

Sulfite also eats into the grain and uncovers latent spots within for the developer to react on. Metol without some sulfite for this purpose, as compared to preservation, loses shadow detail.

Paul;

That is what the previous post said.

As for overall reactions, sulfite generallly makes development go faster!

PE

Thanks.
The particular type of grain I used in my film speed test was the tabular grain Delta 100 ,which may explain why no effect of sulfite on film speed,that might be expected from sulfite uncovering image specks, was detected.

Ole said:

The sulfite is there to prevent oxidation, not counteract it. Sulfite is a very efficient oxygen scavenger.

Click to expand...

I have seen sulphite reverse the oxidation process in some biological reactions, probably the early effects of oxidation form equilibrium products - add sulphite and you tip the balance back. This certainly happens with MQ developers at an early stage.

At a more practical level I used to add extra Sulphite to Ilford PQ Universal (or Su[prol) for spray processing (developing) large images typically 4'x8' and larger, this helped prevent aerial oxidation. I've done the same when sponge developing large fibre based prints, I have to admit I never noticed any increase in speed of development with more sulphite added.

Ian

What reduces the accutance more, the amount of sulfite per unit volume or the length of time the emulsion is subjected to it?

To make things even more complicated: Accutance developers need local exhaustion for accutance effects to show up. If there is enough developing agent, exhausted developing agent will be replaced by still unexhausted molecules quickly, local exhaustion and accutance effects are less likely to show up.

Therefore, improving sharpness via dilution may be an effect of reducing the concentration of the developing agent as well as the sulfite. Both aren't easily told apart as long as you don't make up formulations where you vary one while keeping the other constant.

best

Stefan

Photo Engineer said:

Alan, this range is too narrow to test either the keeping or the solvency effects. A better example would be to test keeping and sharpness/grain at 0, 10, 20, 40 and 80 g/l or some series like that. And, you have to keep the pH constant.

Then, you have to do direct comparisons of identical scenes.

PE

Click to expand...

Or step tablets.

Well, actually a step tablet cant give you a good idea of acutance so you need a definition chart as well. A photo usually has enough fine detail that some sort of information can be derived and in-camera shots are easier than on-easel charts of any sort.

PE

This has been discussed before. The oxidized form of Metol, for example, retards development. At constant pH=8.7, experiments reported in "The Theory of the Photographic Process" show that as little as 6 grams of sodium sulfite/liter will nearly maximize the activity of a Metol developer of about the same concentration as D-23. The presentation tells nothing about grain or acutance variation with sulfite. The same experiments tested ascorbic acid and found that the same molecular concentraion, about 8.5 grams, gave the same activity as the sulfite, but it was theorized that the sulfite acted to form the Metol sulfonate while the ascorbic acid acted to reduce the oxidized Metol back to Metol. Still, no comparison was made of effects on grain or acutance.

We can assume that the 100 g/l of sulfite in D-76 was arrived at by the scientific method or we can pretend it was done because it seemed the thing to do and do some tests to see if a smaller amount would make a noticable difference in any of the qualities we have come to expect from D-76. Remember to keep pH constant.

As noted above, D-76 contains 100 g/l of sodium sulfite. But D-76 is a classic fine grain developer where the high sulfite content is used as a solvent. D-76 also exhibits considerable physical development, where the dissolved silver is replated onto the developed silver. This use of high sulfite concentrations makes an outstanding fine grain developer with excellent sharpness, but it is not an acutance developer with enhanced edge effects. It was noted above that T-grain films are supposed to be intolerant of high sulfite levels, but when diluted 1+1 D-76 does an excellent job with T-Max films. 50 g/l is still a pretty high sulfite concentration.

Acutance developers generally rely on local restraint, local exhaustion, and low silver solvency to do their thing. To achieve this, they are usually used at high dilutions and with modest agitation. At high dilution, the halide released during development from the silver salts in the emulsion can act as a local restrainer. Similarly, the developer becomes locally exhausted. These factors result in a compensating effect and a local reduction in contrast. The lack of a silver solvent means that silver is not removed from dark areas, such as the enhanced lines at dark edges. From what I have read, the edge effects are more a characteristic of the emulsion than of the developer (not all emulsions exhibit them), but the developer can suppress them to a large extent. Acutance developers are formulated not to suppress them.

Indeed, sulfite has many effects in developers: it inhibits aerial oxidation; it prevents staining by the oxidation products of phenolic (e.g. hydroquinone or pyro) developing agents; its concentration has an effect on the tanning of gelatin emulsions by phenolic developers; it affects the activity of the developer; it helps in the regeneration of some developing agents; in some cases and with some developing agents it can increase emulsion speed; and in high concentrations it acts as a silver solvent and helps promote solution physical development. I have seen the effect of sulfite on grain structure - it seems to promote filamentary growth, but things like sodium chloride can inhibit that. The effects seem to be quite complex, and there appears to be a lot of alchemy involved in the selection of sulfite concentrations for various developers. I suspect the effects can be quite different with different emulsions. When making a new developer, controlled experiments are obviously needed.

It looks like the optimal sulfite in the working solution for phenidone or dimezone with ascorbate acutance developers is about 3-5 g/L.In FX-55 it is about 3.7 g/L ,also Ilfosol-S, IIRC it is diluted 1:9: Dead Link Removed

There was a time when edge effects were considered a nuisance to be avoided, not enhanced. The human eye adds edge effects to sharp borders between light and dark. I have before me a photo that I would swear had edge effects, but when I look at the edges with a high quality magnifier they disappear. I'll try to post it, but I doubt that the resolution will allow you to see what I see in the original.