Thermal coefficients of developing agents?

[Paul Verizzo]

I can recall a small chart in one of my photo reference books and/or notes, but I'll be damned if I can find it.

It's a small list of, well, thermal coefficents of developing agents. For a given change in temperature, how much the developing action changes. For instance, hydroquinone has much more increase/decrease per degree change that metol.

I'm looking for metol and ascorbic acid; I do have my doubts that the latter was in the list.

Then there's a spinoff question: In a superadditive combination, would higher temperatures lead to the HQ becoming more active and would that just mean more metol (or phenidone) rejuvenation, or is there some distortion due to the different coefficients?

I notice that an Ilford publication uses the same temperature-time chart for both ID-11 and Perceptol. Either there is no difference whether Metol only or superadditive, or in the range of the charts it doesn't become an issue.

???

 

[gainer]

I think there is such a list in Hardy & Perrin's "Principles of Optics". I'll see if I can scan it and post it. The general rule of thumb that we learned in Physical Chemistry was that each 10 degrees C of temperature ichange cause a factor of 2 change in rate of a reaction, IIRC. Since that was 60 years ago, I can't guarantee that IRC.

 

[Paul Verizzo]

I think there is such a list in Hardy & Perrin's "Principles of Optics". I'll see if I can scan it and post it. The general rule of thumb that we learned in Physical Chemistry was that each 10 degrees C of temperature ichange cause a factor of 2 change in rate of a reaction, IIRC. Since that was 60 years ago, I can't guarantee that IRC.

Thanks, Patrick. I've never heard of that volume, so I know my recollection didn't start there.

I'm familiar with Haist (I've scanned the chapters I'm most interested in), Mason (I own it), and Jacobsen (assorted copied pages.)

Any thoughts on the linearity/non-linearity of superadditive mixtures?

 

[gainer]

I was wrong about Hardy & Perrin. The table that stuck in my mind was in a 1941 War Department Technical Manual of Basic Photography. This is a function which plots on semi-log graph paper as a straight line over the range of temperatures we would be using, so if you find experimentally the development times that give the same contrast index for two different temperatures, you can get a sufficiently accurate line on the graph. This is shown in the Ilford time-temperature graphs. I have a chart that shows the same sort of lines for all the Kodak films except XTOL, But I don't remember where I got it. Probably a Google search. The slopes of the lines would be hard to predict from the developer formula. DK-50 shows the least effect of temperature. It follows the rule of thumb pretty well at full strength, but at 1:1 its coefficient is 1.6. The factor for D-76, D-76 1:1, Microdol X and DK-60a is about 2.5. The factor is 3.1 for D-23, and 3.4 for D-25.

The log transformation is linear, at least for practical use.

 

[gainer]

PS: The graph shows log(time) vs temperature.

 

[T Hoskinson]

I can recall a small chart in one of my photo reference books and/or notes, but I'll be damned if I can find it.

It's a small list of, well, thermal coefficents of developing agents. For a given change in temperature, how much the developing action changes. For instance, hydroquinone has much more increase/decrease per degree change that metol.

I'm looking for metol and ascorbic acid; I do have my doubts that the latter was in the list.

Then there's a spinoff question: In a superadditive combination, would higher temperatures lead to the HQ becoming more active and would that just mean more metol (or phenidone) rejuvenation, or is there some distortion due to the different coefficients?

I notice that an Ilford publication uses the same temperature-time chart for both ID-11 and Perceptol. Either there is no difference whether Metol only or superadditive, or in the range of the charts it doesn't become an issue.

???

Paul, are you referring to the Arrhenius activation energy? for the developer (Arrhenius Rate of Chemical Reactions).

I have a list somewhere for some of the popular developer formulae and the necessary equations. I'll post them when I find them.

Determining the Arrhenius reaction rate for a chemical reaction was a common undergraduate chemistry lab exercise.

 

[Alan Johnson]

Mees & James 3rd edn p371 has a table of temperature coefficients.D-76 is 2.8 .Metol-sodium carbonate is 2.3 at pH 9.85.It does not list hydroquinone alone or any ascorbates.Obscure developers vary between 1 and 5.

 

[T Hoskinson]

Mees & James 3rd edn p371 has a table of temperature coefficients.D-76 is 2.8 .Metol-sodium carbonate is 2.3 at pH 9.85.It does not list hydroquinone alone or any ascorbates.Obscure developers vary between 1 and 5.

Yes, I believe that these are the thermal acceleration factors obtained from solving the Arhennius Chemical Reaction Rate equation.

 

[Alan Johnson]

And the Stokes Einstein equation for the variation of diffusion coefficients with temperature.No wonder the thermal coefficients vary.