Temperature-Drift Musings...

[John Layton]

Sometimes I wonder...to what extent is the tremendous variety of our film processing times for a given developer, regardless of N, N-, or N+ intentions, due to an equally tremendous variety of environmentally influenced temperature drifts experienced by forum members...especially those using open trays? Keeping in mind that these darkroom environments are all over the place...as are we.

Of course, with an equal variety of personal/artistic aims, goals, tastes...one would only expect at least some such variety. But still I wonder. Googling processing times for given developers at given times/temps/dilutions, even when researching "normal" (N) development scenarios, can give vastly different results (times).

I bring this up now as I've recently changed my open-tray routine...from batch processing in a single tray to placing films into individual trays - and have noticed (and have re-adjusted for) an even greater degree of temperature drift with this new routine.

Sometimes I also suspect that there may be inconsistencies in the shelf-life of some pre-mixed chemistry runs, either relating to quality control variables and/or to simply having sat on a shelf for too long prior to sale...but I don't want to point fingers here.

Any thoughts?

At any rate...I would urge folks who have not done this - to do a temperature drift test: fill your regular processing tray with the "correct" volume of water, and "process" your usual number of "practice" films (reject images, etc.) in your usual way...noting the temperature change, and the rate of this change, over your proscribed processing time - and from this establish an average mean temperature...one which considers not only the average temp. but also the rate of change over time.

[Doremus Scudder]

Hello John,

I have done precisely what you suggest, i.e., I measured temperature before and after developing on a rather warm day here in Vienna. Ambient air temperature was close to 30°C and the processing temperature started out at 20°C. I use 5x7 trays with 500ml solution in them. The developer tray is also placed in an 8x10 tray of water at processing temperature. I was surprised that for a 9 minute developing time (plus the 5+ minutes the developer sat in the tray while I was unloading holders and pre-soaking film; i.e., 14 minutes or more total) the temperature increase was just over 1°C. Since most of my developing is done at ambient temperatures much closer to processing temperatures, I concluded that temperature drift was a very small variable in my processing. I process six sheets at a time, shuffling through the stack every 30 seconds, so there is a fair amount of exposure to the air. I'm thinking that the resulting cooling due to evaporation plays a role in keeping the temperature drift lower in warmer air temperatures. Drift might be more if one developed one sheet at a time in a tray and agitated by rocking the tray.

At any rate, for me, temperature drift is a non-issue. The bigger problem is making sure all solutions remain close to the same temperature for several batches. For example, when the air temperature is 25-30°C and I have several batches to do, the stop bath and fixer will rise in temperature considerably over the course of the few hours of processing. What I do in that case is mix my developer at the temperature of the stop and fix and then adjust the developing time appropriately using the Ilford time/temperature conversion chart. A couple of degrees Celsius makes a rather large difference in developing time. This (especially at the end of the developing session) virtually eliminates temperature drift, since the solutions are all close to the ambient temperature.

As far as inconsistencies in chemistry goes; I have two batches of PMK that are markedly different in activity and I've had to compensate. One is a dry-powder kit from Photographers' Formulary, the other is a liquid kit from Lotus View Camera here in Austria. The latter is a bit less active and I've compensated by increasing the amount of solution B till the activity approximates the PF kit. Water quality makes a difference here for some developers too. Earlier I had to adjust developing times about 10% between the harder water here in Vienna, with its higher calcium carbonate component, and the very soft water I had in my former residence in Oregon. My present house in Eugene has water that is just about the same as Vienna water, so times are the same now.

There are a slew of other variables too: changes in film formulation, exhaustion of stock solutions, etc., etc. I try to keep an eye on things but am aware that proper developing is more like a bandwidth of acceptable negative densities rather than a really precise process.

Best,

Doremus

[koraks]

I have done precisely what you suggest, i.e., I measured temperature before and after developing on a rather warm day here in Vienna. Ambient air temperature was close to 30°C and the processing temperature started out at 20°C. I use 5x7 trays with 500ml solution in them. The developer tray is also placed in an 8x10 tray of water at processing temperature. I was surprised that for a 9 minute developing time (plus the 5+ minutes the developer sat in the tray while I was unloading holders and pre-soaking film; i.e., 14 minutes or more total) the temperature increase was just over 1°C. Since most of my developing is done at ambient temperatures much closer to processing temperatures, I concluded that temperature drift was a very small variable in my processing.

Similar experience here, but I have to admit with a tank, not a tray. I rarely do tray development with film, so tank dynamics are more relevant to me. The temperature drift was low enough not to worry about it.

I think other factors such as variations in exposure/metering, differences in judging/measuring the resulting negatives, differences in printing processes to mention a few play at least as important a role as temperature drift, agitation or variations in developer strength (due to measuring/weighing/aging issues). Apart from temperature drift, there is of course also the question what the absolute variation is between the thermometers we all use. I'd be surprised if all posters in this thread were to put their thermometers in the same jar of water and they would all be within 2C from each other...

In short, there are so many variables. Development times posted online can't be trusted to begin with due to a lack of recording of reliable process variables, and even if they could be trusted, someone else's processing times would not necessarily give the result you desire. Still, it's one of those fun things to muse about!

[Luis-F-S]

John I use the Zone VI compensating developing timer so don’t get much inconsistency due to temperature fluctuations. I also keep the darkroom at 68 deg F when I work which also helps.

[Alan9940]

Hello John,

Like Luis-F-S, I use a Zone VI Compensating developing timer; mostly when printing. I use a computer-based compensating developing program when developing film because it allows me to see whatever base temp I need, whereas the Zone VI unit is set to 68F and can't be changed. My film development process depends on what I'm doing. If using the Jobo--which has good temperature control--the only thing I do is place a bagged block of ice in the upper water trough during the summer months which helps keep the water bath at lower temps such as 68F. If processing roll film, I use stainless steel tanks in a large tray of correct temp water; I've found that the large volume of water doesn't change temp nearly as fast. Sometimes I process film at whatever the ambient air temp is, and if I'm feeling really brave and developing, say, 8x10 film I'll use tanks/hangers and go DBI. Lots of different ways to compensate for temperature drift.

[Pere Casals]

The generic ilford graph that is in all datasheets do provide a very good correction, in special for small drifts.

If you start at 20ºC and you end at 21ºC just shorten the development time like if it was 20.5ºC.

Also there is no reason to use open trays, using a paper safe as the tray is pretty convenient, you can open lights and perhaps temperature is more stable.

[Drew Wiley]

For the first 20 years, all my tray processing was done in stainless dimple-bottomed trays in a water jacket kept within 1/10th°F using an extremely dependable Accutemp thermoregulator, then the results densitometer measured. In other words, there were no wrinkles in the process. It was extremely predictable. But that wonderful device finally burned out, and I replaced it with a Calumet equivalent which is a headache to use. Therefore it comes into play only for the most critical applications. For routine work I simply employ drift-by combined with the Zone VI compensating temp probe.

[Pere Casals]

IMHO it's way more critical exposing well than developing a minute more or less, or having temperature half a degree up or down, at the end a bit more or less contrast can be solved in the post process... while a wrong exposure may have way worse effects.

[faberryman]

I would have thought that development variations would have been more influenced by idiosyncratic agitation regimes among users than temperature drift. I have central heat and air and experience little to no temperature drift over the few minutes the film is in the developer. I suspect variation due to inconsistent QC on premixed chemicals, at least among the major players, to be nil.

[Bob Salomon]

I would have thought that development variations would have been more influenced by idiosyncratic agitation regimes among users than temperature drift. I have central heat and air and experience little to no temperature drift over the few minutes the film is in the developer. I suspect variation due to inconsistent QC on premixed chemicals, at least among the major players, to be nil.

Or from your hands being warmer then the water temperature.