Modern Rodinal Substitutes Part II

[Ian Grant]

Apologies for having to start a new thread but I can't read or even access the first to reply to posts.

So with a bit of telepathy

Well, there's a problem there, as it's really hard to measure pH accurately when it gets much above 12.5 or so. You have to start getting special electrodes and the like.

But for MSDS work, it doesn't have to be too precise.
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Kirk

A point that's being missed is that A&O give a figure of 2.7% Potassium Hydroxide not 3% in older Agfa MSDS.

The pH is around 14 sure, but the actual requirement is the pH of the working dilute solution rather than the concentrate which is given elsewhere as pH 11.55, which I commented on in the first post of the thread.

Way back Ron (PE) mentioned adjustments to Rodinal before bottling, the question we need to ask is are they adjusting on the basis of the concentrate, or also doing some tests on a dilute sample, as this will be a far more accurate indicator.

Can someone please post a link to this continuation on the original post.

Ian

[Ian Grant]

Ian, Patrick;

According to my texts, the Sodium Bisulfite available commercially is mostly Sodium Metabisulfite. The same texts do not claim that for the Potassium salt. So, apparently, the Sodium salts are in equillibrium in the solid and liquid state.

PE

In a few previous post I listed the variation of that equilibrium in Commercial Sodium Bisulphite (Kodak and JT Baker - very similar), and the purer Sodium Metabisulphite plus a reference to a Kodak paper on substitution ratio of one for the other.

Potassium Metabisulphite is sold in Home Brew shops and Boots The Chemist (UK) used to stock it. in 250gm Bottles.


Now back to Rodinal

What I was trying to suggest or rather asking is the effects of "the one SO2 and one mole of SO3 upon decomposition in water, both of which end up making HSO3- or the equivalent. It is acidic in water."

I'm referring to the "Orginal formula" Andresen suggests, and many book from Agfa in the early 1900's right through to the recent Darkroom Cookbook.

Yes it's definitely acid until the formulae is balanced with Hydroxide, my point is something different is happening when Metabisulpite's used because of the SO2 & SO3 which won't happen if we used the equivalent amount of Sulphite.

In most developers using small amounts of Metabisulphite it's probably irrelevant but in this old developer with such a high level it has to make a difference.

Ian

[Kirk Keyes]

Yeah - speed and contrast would be really nice.

Inquiring minds want to know!

[Photo Engineer]

Ian;

My point was that the SO3-- reacts to form H2SO3 and SO2 reacts to form H2SO3 (Sulfurous Acid) in acidic solution. If pure SO3 itself is present, then you get H2SO4. The main difference is the final pH and the presence of Sulfuric Acid from any nonionic Sulfur Trioxide which would be minimal in any case.

I think it is mainly the amount of Sulfite present as a preservative and silver halide solvent that is notable here. That is my own opinion though.

PE

[Kirk Keyes]

H2SO3 is dissolved SO2. If the pH is too low, the SO2 is driven out of solution and it's stinky. (I'm on a stinky roll these days.) If the pH is higher, then the SO2 stays in solution as the sulfite ion, SO3--. The SO3-- ion is a good oxygen scavenger, which is one of its main uses in developers, and it is converted to sulfate, SO4--.

In other words, metabisulfite quickly becomes sulfite in solution. If the pH is high enough, there's no free SO2 gas dissolved in the solution. If the solution is acidic enough, you get back the SO2 gas from the dissolved sulfite and you can still have some sulfite ion in solution, but there's not some sort of "metabisulfite" ion present at any time in the solution.

[gainer]

I used to do the step wedges a lot. Many things have happened in the meantime. Things as well as memories have been lost. Ron, did you learn all that you know in school, or is much of it the result of experience and practice? Please don't refer to my lack of education in chemistry. I have had an attack of meningo-encephalitis since then that nearly took me to the pearly gates, and left me having to relearn many things. At least I know enough to ask questions, and am still capable of learning. That I can count among my blessings.

I'll see what I can do with step wedges. I'll have to relearn that as well.

[Kirk Keyes]

my point is something different is happening when Metabisulpite's used because of the SO2 & SO3 which won't happen if we used the equivalent amount of Sulphite.

What's different is that metabisulfte gets you a little more sulfite ion per gram of stuff than bisulfite does and even more than sulfite does - discounting pH effects between the three.

[Ian Grant]

H2SO3 is dissolved SO2. If the pH is too low, the SO2 is driven out of solution and it's stinky. (I'm on a stinky roll these days.) If the pH is higher, then the SO2 stays in solution as the sulfite ion, SO3--. The SO3-- ion is a good oxygen scavenger, which is one of its main uses in developers, and it is converted to sulfate, SO4--.

In other words, metabisulfite quickly becomes sulfite in solution. If the pH is high enough, there's no free SO2 gas dissolved in the solution. If the solution is acidic enough, you get back the SO2 gas from the dissolved sulfite and you can still have some sulfite ion in solution, but there's not some sort of "metabisulfite" ion present at any time in the solution.

So we have a free SO3-- oxygen scavenger in the very early Rodinal type developer Perfect because this helps prevent Dichroic fog and maybe why Anti-foggants needed to be added when they switched to using Potassium Sulphite.

Rodinal is working at "Beutler" like levels of concentration, so the SO3-- is likely to be more critical.

Next point is obviously as the SO3-- is converted in localised areas to sulphate it will harden the emulsion . . . . . . .

So we have a bit of logic for the three distinct phases of Rodinal that we know of:

1 Primitive what we've just discussed "The Classic Formulae"

2 Middle age - ? & when they switched from Metabisulphite to Sulphite, now we see Antifoggant and Bromide needed possibly for the edge effects - Still made by Calbe

3 Agfa/A&O current Rodinal, less p-Aminophenol, higher pH - 14 more bromide etc

That's my theory anyway

Ian

[Kirk Keyes]

Next point is obviously as the SO3-- is converted in localised areas to sulphate it will harden the emulsion . . . . . . .

That seems to be a bit of a stretch... And then why not say that for any developer that has sulfite in it?

[Photo Engineer]

What's different is that metabisulfte gets you a little more sulfite ion per gram of stuff than bisulfite does and even more than sulfite does - discounting pH effects between the three.

This was my point as well but hidden in the chemistry.

PE

[Photo Engineer]

Ron, did you learn all that you know in school, or is much of it the result of experience and practice?

I'll see what I can do with step wedges. I'll have to relearn that as well.

Patrick, after nearly 8 years of college courses in chemistry and hours of lab work there to finish a thesis plus over 40 years of photographic work, (32 at Kodak and 3 in the USAF + working in a photofinisher lab to pay for college) I have to say that I learned every step of the way. I cannot keep it all in memory and have a huge chemistry library here at home at my disposal. It includes a lot of books on photography as well, but I have thrown out most all journal articles.

As for tests, comparison tests would be most useful if you cannot do step wedges. A picture taken and developed with 2 develpers such as Rodinal and Metolal would be nice.

PE