Developer Dilution Time Compensation

[drpsilver]

05 July 2016

I have feeling that this topic has been discussed before, but here I go ...

If one has found a development time, for example using D76 (stock), that works for their process and style, is there a rule of thumb that would give a guess as to how long to develop to give the same overall negative density with D76 (1:1)? Could this rule be used for most developers, or are there limitations? Could this rule be used in reverse, i.e. D76(1:1) -> D76(stock)?

The developers I am most interested in are D76 and Perceptol.

Looking forward to the conversation/discussion.

Regards,
Darwin

 

[Anon Ymous]

The short answer, but keep in mind that it is a rule of thumb, for D76:

Assuming you know the time for D76 stock, then multiply this development time by
1,4 for D76 1+1
1,75 for D76 1+2
2 for D76 1+3

Of course, you can "reverse" this process and get times for stronger dilutions by dividing by the aforementioned factors.

 

[piu58]

You have to distinguish between developpers with redox system and such without. D76 has a redox system (the HQ, which reduces the oxidized Metol), and for such developers can be said: Half the concentration gives an 1.3...1.4-fold time.
Developers without redox system, with only one reducing agent, are nearly proportional: Half the concentration gives double the time. Examples are Rodinal (p-Aminophenol only) and Microdol X or CG-512 (Metol only).

 

[drpsilver]

06 July 2016

Anon & Uwe:

Thanks for your insights on this question. I had not considered the difference between developers with, and without, a redox system. This also gives me some insight into the "chemical action" of developers.

Regards,
Darwin

 

[gone]

With D76, leaving aside the density issue, you're going to get a different look if you dilute it. A little more sharpness, some reduced tonality. At least that's how it plays out w/ my negs. I always use it at stock solution. Probably depends on which film too. I'm referring to Tri-X.

 

[Bill Burk]

I can provide one point of data to support the information already given...

12 minutes at D-76 straight, gives essentially the same characteristic curve for TMAX 100 as 17 minutes in D-76 1:1

This is close to 1.4 times longer development time in D-76 1:1 compared to D-76 straight.

 

[Anon Ymous]

Now, if you'd like the not so short answer...

The development times for D76 seems to be proportional to the square root of the "dilution". D76 1+1 is twice as dilute compared to the stock solution, while D76 1+3 is 4 times dilute. So, sqrt(2) ~= 1,414, in other words about a 40% increase, or multiply the original development time by 1,4 (when using D76 1+1). On the other hand, sqrt(4) = 2, so double the development time if using the 1+3 dilution.