relation between dilution and time?

[luxikon]

Is there a relation between the dilution of a developer and developing time like the proportionality between time and temperature?
If the developing time for stock is 14 1/2 min and for 1+1 is 20 min as for SFX 200 in Perceptol, how long will development last for a dilution of 1+3?

Best
Klaus

 

[Bruce Watson]

Is there a relation between the dilution of a developer and developing time like the proportionality between time and temperature?
If the developing time for stock is 14 1/2 min and for 1+1 is 20 min as for SFX 200 in Perceptol, how long will development last for a dilution of 1+3?

Depends on agitation. For continuous agitation (like rotary development) time usually varies as the square root of dilution. For example, if your time is 5 minutes with a stock developer and you dilute it 1:1, your new time will be (5)(sqrt(2)) = 7 minutes.

For intermittent agitation (like inversion with a small tank), the rule of thumb is that time doubles as dilution doubles. In the example above, your new time would be 10 minutes.

For stand and semi-stand, all bets are off. You'll just have to test and see.

These are of course rules of thumb. You'll need to test to be sure you get the results you want because agitation technique varies all over the place -- everyone seems to do it differently. But at least this gives you some ideas to get you in the ball park. Maybe. Hopefully.

Also, don't forget that you need enough stock developer in your dilution to develop your film. Not enough stock can lead to developer exhaustion which generally looks pretty ugly and is usually fairly erratic since different scenes and exposures need different amounts of the active chemistry. Just sayin'...

 

[Anon Ymous]

Is there a relation between the dilution of a developer and developing time like the proportionality between time and temperature?
If the developing time for stock is 14 1/2 min and for 1+1 is 20 min as for SFX 200 in Perceptol, how long will development last for a dilution of 1+3?

Best
Klaus

I don't think there's a definitive answer. I wondered about it myself recently and had a look at development times for various films in Microdol-X neat and 1+3. The factors were different for every film and varied a lot, from about 1.5x to 2+x. Go figure...

 

[RalphLambrecht]

Is there a relation between the dilution of a developer and developing time like the proportionality between time and temperature?
If the developing time for stock is 14 1/2 min and for 1+1 is 20 min as for SFX 200 in Perceptol, how long will development last for a dilution of 1+3?

Best
Klaus

Klaus

This is a very complex issue. As long as the developer does not run out of active ingredient and consistent and constant agitation can be secured, you might have a chance for a simple equation, but as soon as you have to deal with developer exhaustion, things get rather complicated.

 

[brianmquinn]

Depends on agitation. For continuous agitation (like rotary development) time usually varies as the square root of dilution. For example, if your time is 5 minutes with a stock developer and you dilute it 1:1, your new time will be (5)(sqrt(2)) = 7 minutes.

In theory if you dilute a developer to
2x it’s original volume you need 1.4x the time.
4x it’s original volume you need 2.0x the time.
8x it’s original volume you need 2.8x the time.
16x it’s original volume you need 4.0x the time.
32x it’s original volume you need 5.6x the time.
64x it’s original volume you need 8.0x the time.
If those numbers look like f stops that is because the same kind of math applies.
Also remember that theory and the real world aren’t in exact agreement.

Published times are sometimes more than 1.4X time for a 2x (1+1) dilution but when in doubt develop LESS. A flat negative is easier to print or scan then an overdeveloped and contrasty negative.

 

[RalphLambrecht]

In theory if you dilute a developer to
2x it’s original volume you need 1.4x the time.
4x it’s original volume you need 2.0x the time.
8x it’s original volume you need 2.8x the time.
16x it’s original volume you need 4.0x the time.
32x it’s original volume you need 5.6x the time.
64x it’s original volume you need 8.0x the time.
If those numbers look like f stops that is because the same kind of math applies.
Also remember that theory and the real world aren’t in exact agreement.

Please explain how you arrived at this.

 

[Sirius Glass]

Please explain how you arrived at this.

In theory if you dilute a developer to
2x it’s original volume you need 1.4x the time.[sqrt (2)= 1.4]
4x it’s original volume you need 2.0x the time.[sqrt (4)= 2.0]
8x it’s original volume you need 2.8x the time.[sqrt (8)= 2.8]
16x it’s original volume you need 4.0x the time.[sqrt (16)= 4.0]
32x it’s original volume you need 5.6x the time.[sqrt (32)= 5.6]
64x it’s original volume you need 8.0x the time[sqrt (64)= 8.0]

where sqrt means square root

Steve

 

[brianmquinn]

Please explain how you arrived at this.

It is the square root of 2. I am a chemist (both the type that works in the pharmacy and the type that works in the lab) and that is the way chemistry works. IN THEORY. Use theory as a starting point and do your own tests. Science is about trying to find "rules" but often the rules we scientists find are not hard and fast.

 

[RalphLambrecht]

In theory if you dilute a developer to
2x it’s original volume you need 1.4x the time.[sqrt (2)= 1.4]
4x it’s original volume you need 2.0x the time.[sqrt (4)= 2.0]
8x it’s original volume you need 2.8x the time.[sqrt (8)= 2.8]
16x it’s original volume you need 4.0x the time.[sqrt (16)= 4.0]
32x it’s original volume you need 5.6x the time.[sqrt (32)= 5.6]
64x it’s original volume you need 8.0x the time[sqrt (64)= 8.0]

where sqrt means square root

Steve

Steve

I can do the math, but I wondered where the sqrt assumption comes from.

 

[RalphLambrecht]

It is the square root of 2. I am a chemist (both the type that works in the pharmacy and the type that works in the lab) and that is the way chemistry works. IN THEORY. Use theory as a starting point and do your own tests. Science is about trying to find "rules" but often the rules we scientists find are not hard and fast.

Got it, thanks. Is this similar to the assumption that 10 degrees of temperature half or double the chemical activity during development?

 

[Ian Grant]

Unfortunately Ralph the theory is rather too rough, so for some Film/Developer combinations the difference in dev time between Full Strength & 1+3 is an addition 50% while with others it's 2.5X or +150%, sometimes more.

Perceptol is one developer which differs depending on the film type in use.

Ian

 

[luxikon]

Ian,

you wrote: Perceptol is one developer which differs depending on the film type in use.

Do you happen to know how much it is for Ilford SFX 200 (1+2 and/or 1+3)?

Klaus

 

[Ian Grant]

In theory 25mins 30secs @ 1+2 and 31 mins @ 1+3, but you may run into problems at these dilutions, and times, which is why they aren't recommended. The developer may suffer from severe compression which you really don't want with this film.

Ian

 

[jeffreyg]

It is my understanding that the time, temperature and dilution combinations are suggested recommendations and a starting point from which you would modify as necessary to achieve a desired result. Consider also contrast and equipment ie shutter speed accuracy. Let you eye be the judge as opposed to a calculator.
Jeff

 

[brianmquinn]

It is my understanding that the time, temperature and dilution combinations are suggested recommendations and a starting point from which you would modify as necessary to achieve a desired result.

Let you eye be the judge as opposed to a calculator.
Jeff

EXACTLY

 

[brianmquinn]

One problem is people assume if you dilute the developer in half you need to double time.
This is not true and here is an oversimplified way to look at it.
Assume 1000 developer molecules are in each cubic cm of developer.
10 high x 10 wide x 10 deep = 1000 developer molecules total.
So there are 10 developer molecules on each face of this 1 cm cube.
Only the molecules on the surface that touch the flat film can develop it.
Now dilute this developer in half so there are only 500 molecules in the 1 cm cube.
8 x 8 x 8 = 512 so now we have 8 on each face in spite of the fact that it was diluted in half.
8 in still quite close to 10. So we do not need to develop then film much longer when it is diluted in half.

 

[Martin Aislabie]

A few weeks ago I had did some analysis on dilution v time relationships

I came to the conclusion - there wasn't one

There is a film+dev dilution v time relationship

The time increase from Neat to 1+1 varied from 1.1 to 1.9

The time increase from Neat to 1+3 varied from 1.2 to 2.9

Those film/dev combinations that had a low value of increase between Neat to 1+1 usually but not always had an lower increase from Neat to 1+3

Clearly there are some complex issues going on during development and simple relationships of "an extra 40%" might be a good starting place but is really nothing much more than an Urban Myth

Martin

 

[2F/2F]

IME, the only extremely worthwhile relationship between dilution and time is the one that you determine for yourself by putting in the time (and money) for personal testing. The rest of this stuff is only to determine good starting points for your own tests. We all know this by now, I think.

For HC-110, I used the "double the dilution, double the time" rule of thumb as a starting point when I began using it 1:63 instead of 1:31. In this particular case, it was close, but not exact. (All intermittent hand agitation in cylindrical Nikkor tanks, using an initial one minute of agitation, followed by Ilford's 50 sec. sitting, 10 sec. agitating routine.) I found that I needed about a minute more than double the time to get roughly the same contrast. I say "roughly" because one of the reasons to use various dilutions is the slight effect it has on the shape of the characteristic curve, so contrast will never be exactly the same. That is the point of using various dilutions, IMO.

 

[Ronald Moravec]

Every time you cut the developer 50 % from stock to 1:1 and then 1:3, Multiply the time buy 1.4. The first jump is accurate 1.4. The 1:3 seems to work out way short for me so the theory falls apart for 1:3.

D76 and Delta 100- stock 9 min 1:1 is 12 1:3 in theory is 22, from the data book Ilford gave me 15 years ago.

My times are 6.5 9.75 and 16. This is for a Nikkor tank 10 sec @ 60 inversion 68 deg. Condenser enlarger #2 paper

The times have been worked out with step wedges, densitometer, and actual printing with a standardised test taget illuminated with studio flash.

You need 4 oz of D76 so 1:3 requires a 16 oz tank, 4 oz D76 12 oz water.

 

[Ian Grant]

The theory falls apart as soon as you use different films or developers. Things like pH buffering change with dilution, as the sulphite level drops the dev activity spkes as in 1+3 in some cases, it might be a straight line graph in theory & practice but the slopes differ.

Ian

 

[michaelbsc]

One problem is people assume if you dilute the developer in half you need to double time.
This is not true and here is an oversimplified way to look at it.
Assume 1000 developer molecules are in each cubic cm of developer.
10 high x 10 wide x 10 deep = 1000 developer molecules total.
So there are 10 developer molecules on each face of this 1 cm cube.
Only the molecules on the surface that touch the flat film can develop it.
Now dilute this developer in half so there are only 500 molecules in the 1 cm cube.
8 x 8 x 8 = 512 so now we have 8 on each face in spite of the fact that it was diluted in half.
8 in still quite close to 10. So we do not need to develop then film much longer when it is diluted in half.

Quite an excellent explanation. Obviously the assumption is that no other variables change, as has been pointed out by others. But even though the 'other unknowns' like the pH buffering capacity may skew it a little, this is still an excellent explanation for something I never truly understood before. It completely escaped me that we're dealing with the surface area presented to the active ingredient. Duh!

MB

 

[Thomas Bertilsson]

All math aside, here is another way of thinking about it, which was presented to me by one of my mentors. And up front let me say that I don't ever vary developer temp to alter results. I always process at 70*F.

Agitation is in fact the primary contrast control in film developing. I judge how the contrast in the scene I photographed needs to be processed. If high contrast, I let the agitation intervals become longer in duration, and the opposite if the contrast was low.
Then, the total duration of development is a side effect of the changed agitation and must be altered as agitation intervals are changed.
In summary it's agitation that is the primary contrast control, not the duration of the whole development cycle.

Works for me. I never mess with dilution. I replenish Xtol, which is probably similar to Xtol 1:1 in strength.

- Thomas

Edit: Take lots of notes.

 

[RalphLambrecht]

All math aside, here is another way of thinking about it, which was presented to me by one of my mentors. And up front let me say that I don't ever vary developer temp to alter results. I always process at 70*F.

Agitation is in fact the primary contrast control in film developing. I judge how the contrast in the scene I photographed needs to be processed. If high contrast, I let the agitation intervals become longer in duration, and the opposite if the contrast was low.
Then, the total duration of development is a side effect of the changed agitation and must be altered as agitation intervals are changed.
In summary it's agitation that is the primary contrast control, not the duration of the whole development cycle.

Works for me. I never mess with dilution. I replenish Xtol, which is probably similar to Xtol 1:1 in strength.

- Thomas

Edit: Take lots of notes.

Given the same developer and dilution, time and temperature (and not the method of agitation) are clearly the most dominant variables, affecting negative contrast. Stand-development may be an exception to this.

 

[Thomas Bertilsson]

Ralph, I understand and I trust your expertise. However, for me, altering contrast is a lot about changing how highlights look in comparison to BOTH shadows and mid-tones. As I slow down agitation and increase agitation intervals to about 3 or 4 minutes, even 5 minutes in extreme contrast situations, I maintain fantastic density in the areas of the negative that are more conducive to develop thanks to time, i.e. tones that are closer to shadows, all while I 'calm down' the intensity in the highlights, which to me seem to be more affected by agitation than anything else (i.e. contrast). As I slow agitation cycles down and spread them out farther, I also adjust total development time, but I view that as a consequence of slowing agitation down, not as a means in and of itself.

What results is a perfect negative almost every time, where I spend a very small amount of time tweaking the prints in the darkroom; most of my prints are very close to straight at Grade 2. I'm not saying you can't achieve this any other way, of course! But for me this approach gives me the consistency and the degree of control that I need to get my negatives in tune with my paper of choice.

 

[RalphLambrecht]

Whatever works is fine with me.

I knew a man who swore that a beer diet helped him to lose weight. It did, because all he digested during this diet was beer. His liver did not like it much.