Your experience adjusting development times for different stock and darkroom temps

[Mike in NY]

I have an unheated darkroom in the basement of the house that is sided by an exposed, above grade wall (the house is built on a slope). As a result, the temperature of my stock solutions on the shelf fluctuate with changes in the darkroom's ambient temperature, especially in winter extremes.

Naturally, the development time of any developer can be lengthened to compensate for solution temperatures that are cooler than the manufacturer's recommended developing temp (usually 68 degrees). I often use Ilford Perceptol as my developer of choice, and page 4 of the 2010 data sheet has a text explanation, as well as a graph, about how much to lengthen the development time by the cooler temperature level. It can be viewed at this link: https://www.ilfordphoto.com/amfile/file/download/file/1829/product/708/

The text states to "increase the given development times by 10% for each 2 degrees Fharenheit drop in temperature." However, the graph shows amounts that are greater than this.

Take, for example, the time of 6 minutes at 68 degrees (which is not what I use for Perceptol, but it provides an easy reference for illustration purposes). Let's say you wanted to develop the film at 58 degrees, or 10 degrees below the recommended 68 degrees. Using the text formula, that would involve a 50% increase in development time, from 6 to 9 minutes. But if you look at the graph, the 6 minute mark goes to about 10 minutes at 58 degrees. That's a difference of a full minute between the two recommended adjustments.

I thought that either Ilford is comfortable with generalities, or perhaps the 10% increase in time is supposed to be compounded with each 2 degree interval, which would yield about 9 minutes and 40 seconds.

So I have three questions for those interested in responding to any one of them:

• What is your take on the technical data sheet?
• What has been your experience, if any, with increasing development times for cooler bath temperatures?
• What's the coolest temperature you've developed film in?

Thanks!

[ic-racer]

In the 1980s I used a simple software program that I ran on my Atari ST computer to calculate the times just before I poured the developer into the tank. I print on multigrade paper, so small variations in negative gamma don't matter. Since 1999 I use a Jobo, which keeps everything at the same temp.

[Alan9940]

If developing film using hand tanks, I generally use a temp controlled water bath whether hot or cold. If my ambient darkroom temp is 68F, within maybe a degree or two, I don't bother with the water bath. For sheet film, I use a Jobo. Regardless, I try to keep my film processing in the 65-75F range. I have gone as high as 80F, but worrying about being too cold isn't an issue where I live.

[Jerry Bodine]

This Ilford chart complies with compounding the 10% rule, checking it for your example of 6 min @ 68F, but as you can see the chart only goes down to 64F. Maybe that's an implied suggestion to not develop at temp lower than 64F.

https://www.ilfordphoto.com/wp/wp-co...tion-chart.pdf

[Pere Casals]

The text states to "increase the given development times by 10% for each 2 degrees Fharenheit drop in temperature." However, the graph shows amounts that are greater than this.

Hello Mike,

You should be aware that this is a geometric progression, not an arithmetic one. A*5 is not the same than A^5 (A raised to 5)

So, for an easy way, you may make a repetitive calculation for each 2ºF step increase.

Just use that generic table for corrections. Try to do all at 20ºC, if at end of development temp shifted say 1ºC then you may compensate a bit with time. IMHO the table has to be used for that shift, making the process at around 20ºC its easy and this is the good and consistent way, the corrections are good for the case you have a shift during developement

What is your take on the technical data sheet?

Kodak and Fuji datasheets are technically very, very good, Ilford ones are less technically good but still very, very good in practice and easier understand.

Always read datasheets twice, with a "magnifier". Always we may find interesting information.

What has been your experience, if any, with increasing development times for cooler bath temperatures?

As I use Xtol 1:1 I make the mix of stock with tap water that has the right temperature to make end the mix in 20ºC, if stock is at 18 then make tap water at 22, so it ends in 20.

If you have developer at (say) 16ºC you can place it in a tray and put your hand in (I use a glove if developer is not "eco-friend" Xtol). Your hand is at 36ºC and if you move it a bit then soon developer will heat up.

If developer is at 24ºC then use an ice cube in the developer until it cools to 20ºC, it will add little water, an irrelevant amount.

You can always place developer in a beaker, and the beaker in a hot or cold bath, then stirr until you get your temp.

Use only lower temp if development time is too short for a precise process, a under 5 min development is not recommended, as in that situation time inaccuracies have more relative impact, and we may have a less even development.

What's the coolest temperature you've developed film in?

I made low temperature development (16ºC) with very ancient film, to not soften/damage inestable emulsion, with HC-110 because it's low fog in a situation where fog may be a problem.

Regards,
Pere

[Pere Casals]

Maybe that's an implied recommendation to not develop at temp lower 64F.

https://www.ilfordphoto.com/wp/wp-co...tion-chart.pdf

Perhaps, but also IMHO these are the useful temperatures, not easy that under 18ºC is useful, while we may want 27ºC to shorten a long time from a very diluted developer. So IMHO in general 18 to 27 is what we want to know.

[Willie]

Why not buy an electric heater and get the room to a comfortable temperature before working in it? The radiator type heaters, oil filled, don't put out light or fumes and you can turn it on the day or some time before you will process film and get the chemistry up to temperature so it and you work comfortably.

A few sheets of insulation with something like P2000, a styrofoam board with aluminized mylar on it can be put against the walls. It works well, is lightweight and does not shed dust or fibres like fibreglass will. It is worth looking into for your space.

[Bruce Barlow]

They will pry my Zone VI Compensating Developing Timer out of my cold, dead hands. Or hot hands, if it's summertime. Dead, nevertheless.

[Doremus Scudder]

Keep in mind that hydroquinone, an agent in many developers, loses activity relative to other developing agents at low temperature and increases in activity at higher temperatures at a faster rate than other developing agents (e.g., Metol and Phenidone). In practice, this means that different developers end up with differing temperature/activity coefficients, i.e., the Ilford chart is an average; your specific developer may need more or less compensation.

Best practice, of course, is to find one temperature within the range of activity for your developer and standardize on that. 20°C is lab standard, but there's no reason you couldn't use 19°C or 22°C as long as you are consistent. Choosing one temperature that you can achieve most of the time is the important thing. For those times that temperature has to vary, using the compensation chart will get you in the ballpark, but may not give precisely the same results. If that's good enough, then no problem, but if you need real precision in developing, for whatever reason, then striving for your standard temp is best.

Doremus

[Heroique]

However, the graph shows amounts that are greater than this.

Sometimes, a quick example helps…

For simplicity, let's say for each degree colder, one needs 10% additional development time (a little different than your situation).

1) So, if a given temperature needs 10 minutes, then one degree colder would call for 11 minutes of development time. (10 min. + 10% = 11)

2) And if your temperature is an additional degree colder than that (for a total of two degrees colder), it would be 12.1 minutes. (11 min. + 10% = 12.1)

In other words, two degrees colder doesn't mean 12.0 minutes; it means 12.1 minutes. That's what the chart is trying to say. (Kind of like 10% annual compounding interest in a 401(k) account, great for saving-up for a darkroom in retirement.)

As already mentioned, best is to use charts as a starting point, but over time, record and trust personal results w/ a consistent method – plus a good thermometer and a healthy understanding of its precision vs. accuracy. ;^)