Developer Dilution vs. Dev Time?

kq6up · Apr 18, 2011

Is there a general mathematical relationship to dev time and concentration like there is for temperature and dev time?

For example t=t'*e^(-.045*(T2-T1)) where t' is the original dev time, and T1 is the original temperature given in Fahrenheit. This is usually 68degF.

In chemistry the reaction is defined by the rate equation r=k*[A]^x*^y. Has anyone been able to see this relationship apply in the developing times.

Maybe I can get PE time chime in here.

Thanks,
Chris Maness

kq6up · Apr 18, 2011

Michael R 1974 said:
Wouldn't you need different formulae at least for different types of developers, because they work differently? Just as an example, aside from the type of developing agent, some developers are formulated with much more preservative and or accelerator than others. So dilution affects activity differently, potentially requiring materially different adjustments to time/agitation.

I am interested in Rodinal specifically. I really like that dev, and I would like to be able to extrapolate the times without wasting film. I have been successful in pinning down some other relationships in photography, so I might look into the chemical reaction where 4-Aminophenol reduces Ag+ to Ag, and see if the aforementioned equation works. I am working on that now.

Thanks,
Chris Maness

2F/2F · Apr 18, 2011

This has been discusses at some point, and in will still be in the archives if you search. Yes, some people do have formulas, and a few different ones at that. There is likely to be another argument for which is the best in this thread.

The way I see it, which is pretty non-technically, as long as there is enough developer to completely develop the roll, I just double the time when I half the dilution. Seems to work quite well for HC-110 up to 1:127 and Rodinal up to 1:100. If it's off, it isn't by a whole lot, and it is easy enough to get very close on the second try.

I wouldn't bother with getting into the nitty gritty of the mathematics when you can just guess, and spend a few hours and a few bucks to figure it out. Spend 10 minutes shooting a bracketed sequence of a gray card, guess a time, make a "normal" proofsheet and see if the contrast is right. You also get a working EI this way, which you'd probably want to do anyhow.

kq6up · Apr 18, 2011

I will try it. The math part is just for the sake of knowing what is going on at the chemistry level. I am a chemistry teacher in my day job ;o)

Chris

RalphLambrecht · Apr 18, 2011

This was discussed before, and the conclusion was that this cannot be done easily to satisfaction. You are better of sticking to a couple dilutions and test them at different development times. Then, change the development time to get the desired gradient. Dilution is not a very practical variable, development time is.

kq6up · Apr 18, 2011

RalphLambrecht said:
This was discussed before, and the conclusion was that this cannot be done easily to satisfaction. You are better of sticking to a couple dilutions and test them at different development times. Then, change the development time to get the desired gradient. Dilution is not a very practical variable, development time is.

Yes, I agree in general. I think you are correct. However, looking at the over all trend on the massive development chart. It looks like the reaction behaves as a first order reaction. Therefore, it would be possible to get a ballpark figure to work around, and test for. That is in general (for Rodinal) halving the concentration doubles the dev time. Again, that would be a ballpark approximation.

Thanks,
Chris Maness

RalphLambrecht · Apr 18, 2011

Chris

Develop an equation (3 data points should be a decent start) and try it. Of course, it may not work outside certain limits. But, those limits may not be practical anyway.

2F/2F · Apr 18, 2011

kq6up said:
That is in general (for Rodinal) halving the concentration doubles the dev time. Again, that would be a ballpark approximation.

That's what I do, but I think some people say that 1.4x Time is better when halving the amount of developer in the solution. And, of course, this would only work if there is enough developer present to develop the film. This is often exactly what people are trying not to achieve when using very high dilutions.

There is also a poster here who has done tests and concluded that going any higher than 1:100 with Rodinal has practically no effect on the image that is different than what you will get at 1:100, and just serves to make development time even more painfully long.

In other words, it could be argued that there are only three dilutions of Rodinal that are common and "useful." 1:25, 1:50, and 1:100. So you could probably come up with something that works within that small range.

artonpaper · Apr 18, 2011

There is one other consideration, or perhaps this is what you're hoping to see in the formula. When one dilutes developer more, not all the components have equal energy throughout the developing time. Some components, as I understand it, continue to have a solvent action on grain clumps throughout the developing time, and therefore produce a different grain structure then the shorter time. I think certain developers, HC 110 comes to mind, remain active in the shadows while losing the energy to develop the highlights, thus producing a bit more shadow density while the highlights remain remain less effected by the extended time. This is a very non-technical description, and I'm not a chemist, but my love of doing A-B comparisons has pretty much born this out. I use Rodinal at 1:31.

Lee L · Apr 18, 2011

Stumbled across this from Dickerson and Zawadzki on another forum somewhere, forgotten the source now:

Reply to (titrisol) from Dick Dickerson and Silvia Zawadzki (inventors of Xtol) of Kodak on the question of extending development times with increased dilution of developers.

Your comments about a rule of thumb got us to exploring some old data - some very extensive with Xtol, limited with D-76 and Microdol-X. There is a pattern of sorts. Diluting 1:1 typically adds 40% to the time. 1:2 adds 80% (relative to the undiluted time). 1:3 adds 120% - like tack on 40% for each successive dilution. There is noise around these generalizations, more so as dilution increases, but they would be useful figures to get a person in the ballpark. On the other hand, these generalizations fail miserably with T-Max developer, so it doesn't seem there is any broadly applicable rule of thumb that's safe.

Interesting question all the same. Thanks for sharing!

Dick & Silvia

Lee

piu58 · Apr 19, 2011

There is a big difference between developers without redox system and such with added "accelerator".
If you have only one developing agent you can start with "the time increases as the concentration decreases". This is valid especially for Rodinal: 1+25 needs half the time of 1+50. It is also valid for Metol-only developers.
If you dilute a developer with redox system, the concentration of the acting developer (mostly Metol or Phenidone) near the film surface is less decreased as in the inner of solution. The reason: The concentration decreases in every case during the developing process because the developer is consumed. This will be compensated by the redox system, and it will be overcompensated if you dilute.

For Rodinal I found that you have to change of the developing time by a factor of 1.13 for every degree.

kq6up · Apr 19, 2011

piu58 said:
For Rodinal I found that you have to change of the developing time by a factor of 1.13 for every degree.

I have been using the equation I found on the unoficial HC-110 site:

t=t'*e^(-.045*[T2-T1]) It works perfectly for Rodinal.

Thanks,
Chris Maness

RalphLambrecht · Apr 19, 2011

I don't know how it compares, but the following equation works well for D23, D76 and ID11 when a temperature coefficient (c=2.5) is used:

t2 = t1*c^((T1-T2)/10)

kq6up · Apr 19, 2011

RalphLambrecht said:
I don't know how it compares, but the following equation works well for D23, D76 and ID11 when a temperature coefficient (c=2.5) is used:

t2 = t1*c^((T1-T2)/10)

It is basically the same equation.

Chris

piu58 · Apr 19, 2011

The three formulae yield to the following factors:

Uwe (as mentioned): 1,13 per degree
Maness: 1,11 per degree
Ralph: 1,096 per degree.

Bruce Watson · Apr 20, 2011

kq6up said:
Is there a general mathematical relationship to dev time and concentration like there is for temperature and dev time?

Not really. A big determiner is agitation, a huge topic of its own. But agitation directly effects the diffusion of developer through the emulsion, and the diffusion of development products back out through the emulsion. The OP is a chemist; he/she can probably already see where this is going.

In general (let's say that again -- *in general*), for continuous agitation, development time varies as the square root of dilution, all other things being equal. For example, if your normal time is 5 minutes, and you triple dilution, your new time is (5)(sqrt(3)) = 8.7 minutes.

For intermittent agitation (like inversion agitation with small tanks) the general rule of thumb is that development time varies directly with dilution. For example, if you double your dilution you double your time.

For stand and semi-stand development, all bets are off. Testing is the only way to find out.

Clearly, all this does is get you to a place to start testing. To nail it, you have to test your personal work flow. No other way really.

kq6up · Apr 20, 2011

Bruce Watson said:
Not really. A big determiner is agitation, a huge topic of its own. But agitation directly effects the diffusion of developer through the emulsion, and the diffusion of development products back out through the emulsion. The OP is a chemist; he/she can probably already see where this is going.

In general (let's say that again -- *in general*), for continuous agitation, development time varies as the square root of dilution, all other things being equal. For example, if your normal time is 5 minutes, and you triple dilution, your new time is (5)(sqrt(3)) = 8.7 minutes.

For intermittent agitation (like inversion agitation with small tanks) the general rule of thumb is that development time varies directly with dilution. For example, if you double your dilution you double your time.

For stand and semi-stand development, all bets are off. Testing is the only way to find out.

Clearly, all this does is get you to a place to start testing. To nail it, you have to test your personal work flow. No other way really.

Thanks. That is very helpful. I was just looking for a ball park starting point. I made a bad assumption in thinking that 30' was too short for stand developing, but I decided to reduce the time down to 34' instead of figuring out a more dilute mixture to control the contrast. It turned out that 34' is not too short to get even development in the stand process. I did this because time is a more consistent way of controlling contrast. After all of the advice, I was still interested for academic reasons, and who knows -- it my come in handy.

I understand that this is a ball park figure, but that it would at least be a starting point that could be refined by testing. Any time you have a better guess it saves on wasting materials, and the price of silver has been increasing lately.

Chris

Lee L · Apr 20, 2011

I'll attach an Agfa Rodinal .pdf for times and temps with different films. Most films only give times for 1:25 and 1:50, and the target gamma is 0.65. So I've taken the films that reached 0.65 at 1:100 and put those small tank values (or a couple of interpolated values for 1:100) into a spreadsheet and plotted them.

Note that many films have a rather low maximum density with Rodinal, and so asymptotically approach a somewhat low maximum gamma. I've included the gamma vs. time curve from Agfa's data sheet for Agfapan APX 400 to show that.

You can do your own figuring on how best to model Rodinal time vs dilution or whether it's worth it from this data.

Lee

kq6up · Apr 20, 2011

Thanks Lee

Lee L · Apr 20, 2011

You're welcome. As you can see there's not a clear 'one size fits all' solution for adjusting time for different dilutions, but once you know your film in Rodinal, you can do a quick regression to get you close enough for that film. BTW, since the subject has been broached already, the Agfa times are all based on 5 seconds agitation every 30 seconds. Also, with Rodinal you may find that with some films and concentrations, it may be pointless to go to long stand development times. The combo may have hit the maximum density/gamma wall well before you pulled the film. You'd have to test to find out. The curve shape can also change with stand development.

Lee

Developer Dilution vs. Dev Time?

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