The effect of sulfite in paper developer formulas?

I'm trying to understand the exact role and methodology of using sulfite in paper developers. I know of course that sulfite has a few properties:

* Assists/enables super-additivity with hydroquinone and other (phenol based) developing agents
* Preserves the developing agents / protects from oxygen
* Is a silver solvent making grain finer
* Can be used for pH balancing purposes

However, I've seen huge variance on the amount of sulfite used in paper developer formulas. Because the silver solvent effect is rather minor, one would think you could just load it up with a huge amount of sulfite and call it good and have a very good preservative effect in a developer and no real downsides. In a film developer doing that of course would round off the grain too much, but in paper that effect would barely be noticeable I would think.

The only developers I've ever seen with an explanation attached to sulfite content is lith developers, because of course sulfite prevents infectious development there. However for normal developers I've never seen "add more sulfite for effect X" or "add less for effect Y" like I have for various other ingredients like developing agent and restrainer amounts.

What else does sulfite do? My own theory is that sulfite content may have an effect in determining if a developer is "cool" or "warm".. And maybe too much sulfite can restrain development in some cases. And maybe too much sulfite, especially in glycin developers, can cause dichronic fog. However, I've seen no real explanation to any of these effects. The only property I ever seen mentioned for sulfite in a print developer is as a preservative.

Any silver solvent will make a developer more active, you can interpret silver solvents as the straight opposite of restrainers. Since most traditional paper developers use loads of straight Sodium Carbonate instead of some elaborate buffer system, there's a chance, that adding more sulfite might have raised fog levels.

BTW lowering granularity is not a concern in photographic printing. Photographic paper is very low ISO, which means much finer grained than most photographic film, even before you start accounting for the effects of enlargement.

@Rudeofus Granularity isn't an issue per se in paper developers, but lower granularity may affect image tone, to the warmer. Or would the effect be negligible in this case compared to other methods?

Rudeofus said:

Any silver solvent will make a developer more active, you can interpret silver solvents as the straight opposite of restrainers. Since most traditional paper developers use loads of straight Sodium Carbonate instead of some elaborate buffer system, there's a chance, that adding more sulfite might have raised fog levels.

BTW lowering granularity is not a concern in photographic printing. Photographic paper is very low ISO, which means much finer grained than most photographic film, even before you start accounting for the effects of enlargement.

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On the contrary lowering the granularity is important in warm tone paper development although this is usually controlled by increased bromide and increasing exposure and cutting development. The final image colour/tone is dependent on the fineness of the grain.

Ian

If I compare warm tone to cold tone print developers, these rarely differ in their sulfite content. If you compare neutral tone developer ID-62 with warm tone developer ID-78, their sulfite contents and recommended dilutions are identical. Rafal references an experiment by Ian Grant here (couldn't find the original source), in which Thiourea, a strong solvent, added to PQ developer creates a purple hue, not the expected yellow/brown tone. The main differentiating factor between cold, neutral and warm tone print developers appears to be choice of restrainer, and as Ian pointed out, a possible combination of overexposure and underdevelopment. Even with these differences in restrainers, modern printing papers barely show a color shift.

Rudeofus said:

couldn't find the original source)

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Found it: https://www.photrio.com/forum/threa...one-paper-developers.47580/page-2#post-691896
It piqued my interest and the example appeals to me. Unsurprisingly there are fogging issues with addition of thiourea which was solved back then by Ian by adding rather copious amounts of benzotriazole. Still, fascinating. I quite like that purple image tone. I wonder if it can be had without resorting to adding large amounts of benzotriazole.

Wow, that's 1.25 milligram of Thiourea and 2.5 gram of Benzotriazole per liter of working solution ID-20! At this concentration Thiourea is rather a foggant than a silver solvent.

That's why I just had to look it up. I've had minor traces of 4% thiourea solution sticking to a syringe fog a piece of film rather badly once. I was surprised to read someone had willingly added it to a developer on purpose, in whatever amount.
Yes, I know sulfur compounds (perhaps even thiourea) are used in emulsion making for speed enhancing purposes, but in extremely low amounts.

Rudeofus said:

If I compare warm tone to cold tone print developers, these rarely differ in their sulfite content. If you compare neutral tone developer ID-62 with warm tone developer ID-78, their sulfite contents and recommended dilutions are identical. Rafal references an experiment by Ian Grant here (couldn't find the original source), in which Thiourea, a strong solvent, added to PQ developer creates a purple hue, not the expected yellow/brown tone. The main differentiating factor between cold, neutral and warm tone print developers appears to be choice of restrainer, and as Ian pointed out, a possible combination of overexposure and underdevelopment. Even with these differences in restrainers, modern printing papers barely show a color shift.

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The problem here is that a PQ variant of an MQ developer is inherently warmer and that caused Ilford issues when they switched a PQ version of ID-20 (powdered) in the mid 1950, there were complainants about changing image tone/colour. As a result they reformulated as ID62 dropping the Bromide level slightly and adding Benzotriazole to curb colour shifts. They also realised that by increasing the Bromide of ID-20 PQ with a slight increase in Carbonate they had an excellent warmtone developer which replace Clorohydroquinne and Glycin formula.

You're right that choice and level of of restrainers, Potassium instead of Sodium salts, and of course Phenidone instead of Metol. I can get quite significant colour shifts with MCC and Polywarmtone and enough with Ilford Warmtone, not like the older Record Rapid with Cadmium though.

I had a large quantity of the last Forte Polywarmtone from the final coating, this was sold before it had been aged, quite greenish to begin with but over exposed and under developed I was getting the near red tones the old RR with Cadmium was capable of (purely by development). I found this by accident but didn't exploit it, I was living abroad only printing on odd visits home so the paper settled.

My developer database needs a few extra Category columns so I can do quick queries and sorts for comparisons, I've been slow updating and perfecting it in the last 2 or 3 years. I've a pile of data and written a lot starting in the late 1970's and heavily updated late 1980's to the late 90's. Remember you're quote what I wrote some years ago

It was easy bending the tones of Warm tone papers with Cadmium in so maybe no-one looked at the effects of Sulphite, and perhaps using Potassium Sulphite maybe an approach. Having said that Neutol WA is almost identical to ID-78 (once sold in powder form) except it (liquid version) uses Potassium Sulphite and Potassium Hydroxide instead of Sodium Carbonate. There used to be a Powder version of Neutol WA as well but this was an MQ developer and not as warm.

There's room to experiment.

Ian

koraks said:

Found it: https://www.photrio.com/forum/threa...one-paper-developers.47580/page-2#post-691896
It piqued my interest and the example appeals to me. Unsurprisingly there are fogging issues with addition of thiourea which was solved back then by Ian by adding rather copious amounts of benzotriazole. Still, fascinating. I quite like that purple image tone. I wonder if it can be had without resorting to adding large amounts of benzotriazole.

Click to expand...

That's actually quite interesting. I had similar looking cool tones in some tests I did, though in scanning I've discovered they were less "cool" and more about the way the human eye sees it. The blacks and shadows were actually almost perfectly neutral, but with some warm/brownish kinda highlights that made the shadows look closer to a very cool almost purple black. You can kinda see the same effect happening in the image posted there by zooming the image and making your hand into a small circle to see just a piece of the image at a time. The highlights are definitely a bit warm, the shadows are more like neutral... put all together, the highlights look closer to neutral and the shadows look purple.. or of course do it more scientifically by using a color dropper on the image, though it's low resolution and JPEG artifacts make that difficult. I tried it and what looks purple-ish to me, is actually quite neutral.. like RGB(60, 59, 57) for a shadow level. The midtones and highlights are warm, tilting slightly toward orange and red, and the highest highlights there do appear very slightly magenta, like RGB(192, 188, 192), but the scan there is very poor and jpeg makes being certain quite difficult. I think RGB is the wrong way to attempt to make sense of it.

Either way, this discussion doesn't really make much sense for how to figure out why one would use a particular amount of sulfite. The only reason for using a lesser amount of sulfite that I can see is due to cost, and of course there is an impact on the amount required for preserving various developing agents

* For a basic metol developer, at least 5g/L is typically used
* For a developer containing hydroquinone, at least 10g/L is typically used (with a few exceptions of "special" developers)
* For a developer with glycin even with other agents, less sulfite can be used, down to 2g/L apparently
* Hydroxide developers with hydroquinone typically have a huge amount of sulfite, one reference used 100g/L

and various things like that. I have a hard time believing that cost is the only reason to reduce sulfite content though. In my next darkroom run I think I'm going to make a very simple developer and slowly increase sulfite content with a step wedge to see at a practical level if sulfite can cause an actual difference in print tone or development speed.