How accurate is using time to compensate for temp?

ITD · May 11, 2008

Something that's always bothered me - just how accurate is using a longer development time to compensate for lower temperatures? (or vice versa)

Maintaining temperatures at anything other than ambient is a nightmare for some reason so being able to forget about that and just keep everything at the current ambient temp and adjust dev times would be really handy. But would I be throwing consistency out of the window?

frotog · May 11, 2008

The short answer - it's not. Print color and local contrast are just two aspects of the print that are affected by temperature. These compensating timers like the old zone iv are based on the faulty premise that time and temp have a reciprocal relationship throughout the tonal scale of the print or neg.

David William White · May 11, 2008

Are you developing B&W only? Are you battling seasonal variations in darkroom ambient temp or daily variations? Do you have a preferred temp you CAN acheive? Are you looking for ideas to acheive ambient temp stability?

ITD · May 11, 2008

David - black and white only, and the variations are daily - I guess if I could consistently achieve a different temp I could use that, but I'm either too high or too low...

I've read lots of different suggestions to maintain temperature, but nothing really does it for me yet - can't avoid wild fluctuations, regardless of the method. You may have ideas I haven't tried yet though!

richard ide · May 11, 2008

In my lab I could machine process prints up to 48" wide. Sometimes a project would include prints under 48" and some wider which I had to hand process. Processor developer temperature was around 100 degrees. If I hand processed with the same developer; the prints matched. I used many different types of paper with no problems. Increasing chemistry temperature only changes the reaction time. The only variable is the processing time. IIRC If you increase temperature by 10 degrees your time is reduced by half.

ITD · May 11, 2008

Richard - would this also be true of film?

richard ide · May 11, 2008

I will give a qualified yes. Colour materials are such complicated structures that there may be a difference, but there again the chemical activity varies with temperature so it should be the same. I do not have enough knowledge about colour to put my other foot there as well. With BW film, emulsion colour is irrelevent unless one uses a developer which stains the negative. The only exception would be BW transparencies for display.

David William White · May 11, 2008

ITD said:
David - black and white only, and the variations are daily - I guess if I could consistently achieve a different temp I could use that, but I'm either too high or too low...

I've read lots of different suggestions to maintain temperature, but nothing really does it for me yet - can't avoid wild fluctuations, regardless of the method. You may have ideas I haven't tried yet though!

I've found the temperature tables given for the common developers (rodinal, hc-110, d-76) are pretty reliable within 18C and 24C. It should certainly be possible for small tanks sitting in a tray of water to hold the temperature within 1C or so for the duration of the development -- say 6 minutes. This shouldn't be too difficult to accomplish.

Tmax developer is a little more temperature critical, I understand, so you may wish to stick with less 'modern' developers.

Jersey Vic · May 11, 2008

I keep all of my B&W chemistry (liquid) in the same space so that the temperature is consistent from prewash through permawash and the temperature in that space is 66-77degrees F 99% is the time. I calibrate my thermometers regularily and when it counts (non-diafine development), I am very precise with my time and temp adjustments. When I follow all of these procedures, I find my negs from the same camera and metered the same way are consistent across the temperature range.

ITD · May 11, 2008

David William White said:
...sitting in a tray of water to hold the temperature within 1C or so for the duration of the development... This shouldn't be too difficult to accomplish.

No, keeping within 1C of a temperature that I haven't chosen is really easy. It's getting anything near 20C when the ambient temperature is anything else (which is most of the time!)

Actually, I've just finished a test roll - the dev temp increased from 20C to 21.7 during the 9 minutes. By the time I had managed to reduce the temperature of the chemicals, the water bath I'd set up for the tank during developing had heated up by 2 degrees...:rolleyes:

Having said all that, this is the reason for my OP - if I can stop fighting the ambient temperature, then life will be easier. I'm not talking a huge variation, maybe between 18 - 24C so if the difference isn't going to be too marked, I'll try this approach.

glbeas · May 11, 2008

If you want best consistancy you need to generate curves for each film developer combo. If I remember correctly the different developer agents react to temperature changes differently. I think hydroquinone nearly dies below 65F where others keep going to some degree, so using one with a mix will give an uneven curve as well as having different characteristics. That said if you work within 65 - 85F with B&W the standard curves are fairly consistant.

ITD · May 11, 2008

I'm not using anything exotic - just D-76 with temperature fluctuations between 18-24C

Tom Hoskinson · May 11, 2008

ITD said:
Something that's always bothered me - just how accurate is using a longer development time to compensate for lower

The Arrhenius equation is a simple, but remarkably accurate, formula for the temperature dependence of the rate constant, and therefore rate, of a chemical reaction.

the Arrhenius equation gives "the dependence of the rate constant k of chemical reactions on the temperature T (in Kelvin) and activation energy Ea

k=A Exp -Ea/RT

I use the Arrhenius equation quite successfully with Kodak and Ilford's published developing time and temperature data for their films and developers to determine the temperature dependent reaction rates.

David William White · May 11, 2008

ITD said:
No, keeping within 1C of a temperature that I haven't chosen is really easy. It's getting anything near 20C when the ambient temperature is anything else (which is most of the time!)

Actually, I've just finished a test roll - the dev temp increased from 20C to 21.7 during the 9 minutes. By the time I had managed to reduce the temperature of the chemicals, the water bath I'd set up for the tank during developing had heated up by 2 degrees...:rolleyes:

Having said all that, this is the reason for my OP - if I can stop fighting the ambient temperature, then life will be easier. I'm not talking a huge variation, maybe between 18 - 24C so if the difference isn't going to be too marked, I'll try this approach.

Out of curiosity, what was your measured ambient tempurature that caused your water bath to heat up by 2C in 9 minutes?

Kodak's data sheet on d-76 lists times for common films from 18, 20, 21, 22, and 24C.

Are you above this range?

Kirk Keyes · May 11, 2008

Get a Jobo.

I have really cold water here except in the summer where the tap temp can get up to 24C. So I just run everything at 24C now, and the Jobo does a great job of holding the temp.

df cardwell · May 11, 2008

ITD said:
I'm not using anything exotic - just D-76 with temperature fluctuations between 18-24C

You can rely on Kodak's published info.
D76 is the gold standard.

ITD · May 11, 2008

David William White said:
Out of curiosity, what was your measured ambient tempurature that caused your water bath to heat up by 2C in 9 minutes?

Kodak's data sheet on d-76 lists times for common films from 18, 20, 21, 22, and 24C.

Are you above this range?

Ambient was around 24C, but I guess some of the increase came from heat in my hands and temperature of the tank when I filled it. The water bath took much longer to increase - it took ages to get the dev temperature down until I could find a vessel that would allow a decent depth of water jacket...

ITD · May 11, 2008

df cardwell said:
You can rely on Kodak's published info.
D76 is the gold standard.

That's good to hear, thanks.

Alan Johnson · May 11, 2008

Here's a curiosity, Rodinal 1+25 has two time vs temperature lines of different slopes for 100 and 400 speed films (Diagram 2):
http://www.silverprint.co.uk/PDF/Rodinal_Leaflet.pdf

nworth · May 11, 2008

Temperature affects both the reaction speeds (there could be multiple reactions taking place) and the rate at which the chemicals penetrate the emulsion. As a result, simple time compensations for temperature do not work exactly. For black and white, they are quite usable, and they produce negatives that are consistent enough for even the fussiest workers. Color is another matter. There is just too much going on when developing a color image. Some processes can be adjusted to work within a degree or two of the target temperature, but some must be right on for reasonable consistency. Even with black and white, extreme compensations for, say, more than 8 or 10C will probably produce noticeable changes in the negatives.

Ray Heath · May 11, 2008

g'day all
surely, given all the other variables, measuring accuracy; mixing accuracy; aesthetics; intent; usage; presentation; and on and on, the good old time/temp chart will be pretty close and give a usable outcome

Ray

srs5694 · May 11, 2008

ITD said:
Ambient was around 24C, but I guess some of the increase came from heat in my hands and temperature of the tank when I filled it. The water bath took much longer to increase - it took ages to get the dev temperature down until I could find a vessel that would allow a decent depth of water jacket...

If the in-tank developer temperature changed from 20C to 21.7C over 9 minutes when ambient temperature was 24C, then my guess is that something you could better control was going on:

The starting tank temperature may have been at ambient, as you mention. Try pre-wetting your film and wait for the temperature of the pre-wet water to stabilize at 20C before developing.
If, as you also mention, your hands were warming the tank and solution, then perhaps you were handling the tank too much. Between agitation cycles, return it to the water bath. If you really think this was a big issue, try minimizing hand-to-tank contact in any way you can, such as by changing from inversion to rotational agitation.
You might not have sufficient volume of water to buffer the temperature in your water bath. I use a dishpan tub (mostly for color developing, but occasionally for B&W), which seems adequate.
Plastic and stainless steel tanks have different temperature characteristics. Plastic tends to insulate better, which could help if you first bring the film and tank to the correct temperature by a pre-wet. OTOH, steel might be superior for getting quickly to the correct temperature via pre-wet.
You might be able to rig something to keep the water bath at a constant temperature. People who do color work often use aquarium heaters for this purpose, but you'd need something else for B&W at typical B&W temperatures. I have no specific suggestions, though.

Tony Egan · May 12, 2008

Ray Heath said:
g'day all
surely, given all the other variables, measuring accuracy; mixing accuracy; aesthetics; intent; usage; presentation; and on and on, the good old time/temp chart will be pretty close and give a usable outcome

Ray

I would agree. I think the science in photography is inherently "sloppy" due to all the variables. I don't mean to say you can be sloppy in technique and expect consistent results but the things some people can agonise over are just not worth worrying about in my opinion. I have used the same Ilford time/temp graph for over 20 years and get consistent results but my technique is always the same for small daylight tank developing.
- Always aim for 20c as the starting point.
- If room temp is higher start solution cooler, say 18-19c.
- If room temp is lower start solution temp higher, say 21-22C
- Temp will stabilise quite quickly after first 60 seconds of agitation
- Measure temperature after first 60 seconds of agitation (it is suprising how often I can get almost exactly to 20c based on experience and "feel" for the room temperature and how warm or cool the tank feels in my hands - I don't pre-wash 35mm film or preheat tanks))
- Measure temp twice again during development (remove cap, stick in thermometer) at approx 1/3 and 2/3 dev time.
- Extrapolate any temperature changes for average movement up or down during development
- Adjust final development time accordingly - usually no more or less than 60 seconds either side of "normal"

I typically use Xtol 1+1 for dev times of 8-12min with 60 sec initial agitation followed by 10 secs every 60 sec.

And we haven't mentioned all the potential variables in exposure to start with: shutter speed accuracy (across multiple lens), zoom effects, metering process, "in-between" aperture choice, age of film etc etc

Doremus Scudder · May 12, 2008

Calling Tom Hoskinson and Frotog!

This discussion has aroused my curiosity about a couple of things. Sorry if this is a "quasi-hijack" to some degree, but I think it belongs here instead of in another thread.

First questions to Tom Hoskinson: Could you give some instruction to a non-mathematician about how to use the Arrhenius equation in this context? What is the difference between Kelvin and Celsius, how can I derive a new time for a different temperature from a known one?

And now to Frotog. I would be interested in hearing what evidence you have to support your statements that image color and contrast are also affected by time/temperature changes. Could you elaborate a bit please?

Thanks in advance to both of you for enlightening me.

Best,

Doremus Scudder

www.DoremusScudder.com

gainer · May 13, 2008

As a matter of interest, the Kodak detailed data for CI vs numerous films vs temperature all plot as straight lines on log-log graph paper. There is a slight amount of scatter which is without doubt due to experimental error. All lines intersect at 0 time. The problem with being too precise is that it is not easy for actual work to be as consistent as the average of a number of runs, and never as precise as the theoretial, though it is possible for the theoretical to be less accurate than the experimentally determined values.

The catch with using this log equation is that one of the constants in the equation is not directly measurable from the experimental data. Also, it's one thing to analyze existing data, and quite another to get data you don't have. In this case, it involves a step density test strip developed under accurately controlled conditions for each of 5 or 6 times and temperatures, each strip to be analyzed by densitometer
readings to get contrast index.

My point here is that the variation of CI with time and temperature is certainly consistent enough to be of good use, but it may be easier in the long run just to control the temperature of the developer.

How accurate is using time to compensate for temp?

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