Formula for figuring out alternative developing times and agitation for film

To start: This is mostly a quest for knowledge about the relationship between dilution, agitation scheme, and development time.

For example, I sometimes read comments like, "I extended development by 30% and reduced agitations to 1 or 2 (or whatever) inversions every 2 minutes" or "I diluted the developer to some not-well-known dilution, increased development time to 24 minutes, and agitated twice every five minutes" -- what I want to know is, did these people just pull these numbers out of hat, or is there some common knowledge that if you increase time (or reduce/change dilution) by a certain amount you should increase/decrease inversions by a certain amount/time?

That is, is there some standard formula for figuring this out?
(using the same dilution(n:n) + n% longer time = n inv for n min agitation scheme?) or (changing dilution (ie. not standard ratios, for example, 1:1 to 3:10) = n agitation + n time?)

I've looked through multiple online sites and all of my darkroom books but have found only one suggestion (from Steve Anchell) that suggests, for minimal agitation, adding 50% development time and then 10sec agitation every 3 minutes. It certainly gives me a good starting point, but doesn't address how others have come up with dilution/agitation/time schemes that don't fit this formula. Most other information I've found is either too personalised, or lacking in any details ("I now use this weird dilution and have great negs but I won't give you the times or agitation technique I use because you should test for yourself." FWIW, I agree, but having a little more info to start with would be nice, instead of having to reinvent the wheel...), or deals with films since discontinued or developers I don't have ready access to.

To reiterate, I'm not looking to debate the perceived (or lack of) usefulness of trying these kinds of combinations. I just want to know how people figure it out, other than basic trial and error.

The trouble with trying to reduce things down to a formula is that there's not really a linear relationship or a formula-defineable relationship between the variables. For example, changing the dilution doesn't change the developing time in the way you would expect.

Yeah, I guess I knew it wouldn't be that easy...

Is there an example of what you're trying to do, or are you just after some general guidelines?

I guess general guidelines. If it helps the developers I use the most are D-76 and Rodinal (now R09). However, I've been working with some new (to me) films and developers and often search the internet for developing times and examples. I've come across some less obvious ones (for Rollei films), tried them, and they worked. But these kinds of alternative dilutions and developing times are not what I normally would have experimented with, as I usually stick with the tried and true and vary certain elements just a little. Since I'm about to start a round of film testing (something I haven't really done much of in the past) it got me curious as to how people make the (educated guess?) of trying these alternatives.

mooseontheloose said:

I guess general guidelines. If it helps the developers I use the most are D-76 and Rodinal (now R09). However, I've been working with some new (to me) films and developers and often search the internet for developing times and examples. I've come across some less obvious ones (for Rollei films), tried them, and they worked. But these kinds of alternative dilutions and developing times are not what I normally would have experimented with, as I usually stick with the tried and true and vary certain elements just a little. Since I'm about to start a round of film testing (something I haven't really done much of in the past) it got me curious as to how people make the (educated guess?) of trying these alternatives.

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You only need to stay on grade 2 for whatever lighting you have on the day. Use ilfords film and ID11 times, or Kodaks and D76 times noting that the developers are the same.
Fixing and washing is way more critical.
Do not chase ghosts in cemeteries.

Hey Noel...I'm not so interested in chasing ghosts or magic bullets, I'm just curious as to how these combinations work.

Rachelle, you might get a hint from Kodak's film datasheets. The "normal" development times they provide are for small tanks and 30'' agitation intervals. They also provide development times for large tanks, with 1' agitation intervals. IIRC, the difference seems to be a ~10% increase in development time.

Regarding dilution, the development times obviously change, but the change isn't the same across all developers. When using Rodinal type developers (possibly HC110 too), the increase seems to be linear, according to the dilution, e.g. double the time when doubling dilution. Others, like D76 and Xtol seem to need a time increase proportional to the square root of the dilution. In other words, when doubling the dilution (1+1) you need to multiply the development time by sqrt(2) ~= 1,4, so about a 40% increase. Bad at math? Just use the following factors as a rule of thumb:

Dilution - Time increase
1+0 (stock) - N/A
1+1 - 40%
1+2 - 75%
1+3 - 100%

Thanks Anon - that information is exactly what I am looking for. Of course, I'm assuming regular intermittent agitation with these formulas.

mooseontheloose said:

Thanks Anon - that information is exactly what I am looking for. Of course, I'm assuming regular intermittent agitation with these formulas.

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I'd say regardless of agitation scheme. Let's assume that you use D76 and increased dilution from stock to 1+2, needing a 75% increase. Let's also assume that you want to switch from 30'' agitation intervals to 1' and a 10% development time because of this. That should be a 10% increase on top of the already increased time, resulting in a 92,5% increase.

Wouldn't that be an 82.5% increase?

mooseontheloose said:

Wouldn't that be an 82.5% increase?

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Nope. A 75% increase is the same as multiplying by 1,75. Likewise, a 10% increase is the same as multiplying by 1,1, but has to be done on top of whatever other increase you must do. So, if you multiply by both factors you get 1,75*1,1 = 1,925. That's how you get a 92,5% increase.

In any case, a 10% difference is not big. Keep in mind that film manufacturers publish rounded development times, sometimes to half a minute...

There are other parameters to consider than simply the effect on development activity of agitation frequency and dilution.

First, an agitation scheme's primary purpose is to provide even development. Insufficient agitation can cause uneven development. So can to vigorous agitation (surge marks, etc.) "Standard" agitation techniques are time-tested and reliable and deliver consistently good results. That's why so many people use them.

However, reduced agitation has a couple of desirable side-effects: compensation and promoting the formation of edge effects. Many spend a lot of time working out developer and agitation for stand or semi-stand schemes just to optimize one or both of these effects. Unevenness is the danger with longer intervals between agitation, so it's tricky and often hit-or-miss at first for these techniques. That said, many of us use some kind of reduced agitation and have consistently great results. You simply have to know what you want and work out an agitation scheme that gives you the desired effect plus even development. For instance, I reduce my tray-shuffling agitation in PMK to only once through the stack every minute (as opposed to 30 seconds) for the second half of the development time. This gives me great edge effects. Once through every minute for the whole time gave uneven development, so I opted to agitate more frequently for the first half and then less frequently for the second half to retain evenness.

Similarly, dilution has secondary effects: With high-sulfite developers like D-76, dilution will affect the amount of grain softening since the sulfite concentration is different. That's why Kodak says to use D-76 full-strength for "fine-grain" negatives but 1+1 for more acutance but more pronounced grain. Also, using a dilute developer promotes compensation; the developer exhausts in the highlight areas (high-density areas) but continues to be fully-active in the mid- and shadow values, thereby developing the higher values less and taming contrast somewhat. Using a dilute developer together with reduced agitation gives more of the compensation effect since there is more time between agitations for the developer to exhaust.

Unless you are striving for one of these side-effects of reduced agitation/dilution, there's not really much reason to vary from the manufacturer's recommendations. If you do, then you'll likely need to test and modify your scheme till it gives you the results you are after.

Best,

Doremus

Of the variables mentioned in the OP agitation is the most problematic. It is not linear in its effect and would defy any attempt to generalize.

As a practical matter each developer responds differently to time or temperature. This is because each developing agent behaves differently. Therefore developers with a single developing agent are easier to predict than more complex ones. Yes there are there are some general trends but developer manufactures usually publish separate curves for each of their products.

Thanks Doremus, Gerald, for confirming what I sort of suspected. As I mentioned in the beginning, I've been trying to figure out why (or how) people come up with widely different developing schemes...I guess in the end, it really is just trial and error with different developers, that there is no systematic way of experimenting, other than doing a lot of it!

Negative development is rather subjective. Different people desire different things like Contrast Index (Gamma). In addition their thermometers or light meters may not be accurate. Best to either stick with the manufacturer's advice or do your own testing.

Development is what is known as a diffusion controlled reaction. Therefore changes in agitation do not always have the desired effect. Diffusion is rather complicated and depends on several parameters besides temperature.

Modelling these kind of variables is quite difficult as they are, for instance, differents ways for agitate. I use D76 stock with minimal agitation with a development times 50% longer than normal agitation. I use Kodak time for my films. It works for me.

Hi Mooseontheloose. I came upon my developing technique by informed trial and error. I copied what DF Cardwell was doing with Rodinal and reduced agitation but could not get it to work as I wanted. I substituted HC-110 and it worked. It is sometimes so personal that it is hard to quantify. It helps if you have a vision in mind of what you are trying to achieve, so look at the work of photographers you admire and see how they do it. What have you in mind for your film testing and what developer will you be using ?