Dilution dilemma

[presspass]

I've read here that a 1.4 factor for dilution gives a good starting time with film developer - from straight developer to 1:1, multiply the straight developer time by 1.4. I'm going to go from 1:1; if I multiply that time by 1.4, will that give me the time for 1:2 or 1:3. Thanks,

 

[kevs]

Hi Presspass,

Which film developer are you using? Developing times are dependant upon the film you're developing, the developer temperature, dilution and the effective film speed. I doubt that many film/developer combinations have linear relationships when it comes to dilutions/development times. The best thing is to use the manufacturers' recommendations as a starting point - they make the products and generally know what they're talking about - why do their work for them? You'll probably find your combo here: http://www.digitaltruth.com/devchart.php - then you can work out the maths for yourself if you really need to.

Cheers,
kevs

 

[presspass]

Kevs,
I've had good luck with D-23 1:1 at 15 minutes, 68º f for Tri-X (Arista 400) at 1600 and D-23 1:3 at 20 minutes, same temp, for same film at ISO 400. I would like a bit longer time for the 1600 to reduce the agitation, but don't want to go to 30/35 minutes 1:3. That's why I was thinking of using it 1:2. The 1.4 factor brings it in at 21 minutes. That was the reasoning. As far as I've been able to discover, there's no recommended time/temp for that combination. Guess I'll just try it and see what happens. Thanks.

 

[tkamiya]

If this is XTOL, you can still get a copy of GERMAN version that lists higher dilutions somewhere on the net. If you can't find it, drop me a note and I'll email my copy for you.

As you go higher and higher in dilutions, you run a greater risk of not having sufficient amount of active ingredients. This is especially true if you are using metal cans for 35mm processing. In such cases, changes won't be linear and in some cases, it won't even completely develop.

My suggestion would be to go back to manufacturer's suggested time per spec, then experiment from there - keeping eyes on minimum requirement of stock solution.

 

[kevs]

Kevs,
I've had good luck with D-23 1:1 at 15 minutes, 68º f for Tri-X (Arista 400) at 1600 and D-23 1:3 at 20 minutes, same temp, for same film at ISO 400. I would like a bit longer time for the 1600 to reduce the agitation, but don't want to go to 30/35 minutes 1:3. That's why I was thinking of using it 1:2. The 1.4 factor brings it in at 21 minutes. That was the reasoning. As far as I've been able to discover, there's no recommended time/temp for that combination. Guess I'll just try it and see what happens. Thanks.

Ah, I automatically thought you were using an off-the-shelf developer, so I'm sorry i was a little terse. I guess the only thing is to experiment. Good luck with it,

Cheers,
kevs

 

[andrew.roos]

I've read here that a 1.4 factor for dilution gives a good starting time with film developer - from straight developer to 1:1, multiply the straight developer time by 1.4. I'm going to go from 1:1; if I multiply that time by 1.4, will that give me the time for 1:2 or 1:3. Thanks,

I can't vouch for the correctness of the 1.4 factor when converting times for straight developer to times for 1:1 dilution. But if it is a good rule of thumb, then I would expect it to go from 1:1 to 1:3 because that halves the concentration of the developer, just as moving from straight to 1:1 dilution does.

As an aside, note that 1.4 is approximately the square root of 2, so you could go from straight developer to 1:3 dilution by multiplyng the time fo rthe straight developer by 2.

 

[polyglot]

Yes, development time goes approximately with the square root of dilution, with a whole bunch of exceptions like exhaustion, agitation effectiveness, changes in superadditivity, etc.