A good temperature conversion table.

Radost · Jan 22, 2023

I have been doing xtol 1:1 at 75F.
Lately it has been cold and my chemical temps are 74F. Is there a formula or a table for time conversion? The Ilford one is skipping degrees.
I tried https://www.digitaltruth.com/devchart.php?doc=timetemp
but in the past their app has given me some wrong times not equal to Kodak times so I don’t trust them.

gone · Jan 22, 2023

For B&W, I would seriously be surprised if one degree F would make any visible difference. B&W is a very lenient and forgiving medium. I use a thermometer just to see if things are somewhere close for film, and never for darkroom work. I used to, it made zero difference in the prints. For color, that's different. The main thing is to try and be consistent, it helps to use the same type of agitation for certain films, etc.

Peter Schrager · Jan 22, 2023

At 74 degrees I would just add one minute and you'll be fine!

guangong · Jan 22, 2023

One degree shouldn’t make a difference. The Kodak Darkroom Handbook has a rotating dial for determining time adjustments according to different temperatures.

ic-racer · Jan 22, 2023

In the early 1980s when I got my first computer, one of the things I did with it was to write software for curve fitting. So I would not have to go to the school's lab [to use the computer there] in the afternoons or weekends to solve my problems for graduate school. For fun I also decode the Kodak Darkroom Handbook temp. wheel.
This is what I came up with. I printed out a table so I would not have to boot up the computer each time I wanted to process film.

New Time = (x * B + y) * Log (New Temp) + B

Where:
B = (Old Time - (Old Temp * y) / (1 + Old Temp * x)
y = -0.576929
x = 0.620567

gone · Jan 22, 2023

Of course the next question is, are you actually diluting your developer to be 1-1? Wouldn't that give you 0 of developer? In that case, temperature differences should be moot.

Or did you mean 1:1, which (using 1:9 just for an example), many people say means 1 oz of developer is diluted w/ water to get 9 total oz. Or 1+1, which means, going back to my example, 1 oz of developer to a ratio of 1+9, so you now have 1 oz of developer plus 9 oz of water to get a total of 10 oz.

Some say that Kodak has been confused on this for a long time, and uses the two different ratios interchangeability. On that one, there should be no confusion that Kodak has been confused.

RalphLambrecht · Jan 22, 2023

momus said:
For B&W, I would seriously be surprised if one degree F would make any visible difference. B&W is a very lenient and forgiving medium. I use a thermometer just to see if things are somewhere close for film, and never for darkroom work. I used to, it made zero difference in the prints. For color, that's different. The main thing is to try and be consistent, it helps to use the same type of agitation for certain films, etc.

right. I doubt 1ºF even makes a measurable difference; never mind visible.

AZD · Jan 22, 2023

Ilford’s developer packages have charts included, and they roughly correspond to 1 minute per 1 degree C. Chances are with development times around 8-10 minutes and a variance of only one degree, your own accuracy will be less than the chart.

That said, to repent for my past sins of sloppy processing, I now use a water jacket (big metal pan) for development with enough water to provide a consistent temperature, and I do occasionally subtract a minute or two when the summer water temperature is higher than 20 C. So far so good.

Sirius Glass · Jan 22, 2023

In the book I keep my darkroom notes I made a table of the temperatures and time for each film with replenished XTOL and use interpolation to fill in the missing times. Do it once for each film and then just look it up in the table.

faberryman · Jan 22, 2023

You could probably plot the relevant time and temperature information for your film and preferred contrast index from the Xtol datasheet on a sheet of graph paper and draw the curve connecting the dots in about five minutes. Put it in a page protector and save it for future use.

MattKing · Jan 22, 2023

momus said:
Some say that Kodak has been confused on this for a long time, and uses the two different ratios interchangeability. On that one, there should be no confusion that Kodak has been confused.

Nope - "component volume : dilutant volume" is used by many in many circumstances, within and outside the photographic world.
Whereas "component volume : total volume" is used by others in many circumstances, within and outside the photographic world.
For communicating with others, potentially in different geographic areas and whose first languages and experiences will vary, and whose context may vary, where the dilutant is water, it makes sense to use an "A + B" notation. Where Kodak directions include a word description as well as the "A:B" notation, the words used mirror the "A + B" approach.

Doremus Scudder · Jan 23, 2023

Back to the original question:

I agree with the others above that one degree F won't make a huge difference. It's worth noting that the Ilford chart is based on degrees Celsius and that the values given in Fahrenheit are rounded numbers. Yes, 20°C = 68°F, but 21°C = 69.8°F and 22°C = 71.6°F (not 72°F), etc.

However, if you want to be more precise than that, here are couple of suggestions.

Use the Ilford chart to come up with a factor for each degree Celsius, i.e., a value that you multiply the previous temperature by to arrive at the second. Then, convert this to F by using the good old 10°C = 18°F rule and then use that to determine how much you need to change development when the temperature varies by 1°F.

Alternately, if you can't heat your developer up to 75°F, you can cool it down to 71.6°F. Then just use the Ilford chart time for 22°C. I might try processing at a lower temperature anyway unless you're using a processor that simply won't go lower. B&w processes were designed for 20°C.

Or just use your usual time plus 5% and be done with it.

Best,

Doremus

Radost · Jan 23, 2023

Doremus Scudder said:
Back to the original question:

I agree with the others above that one degree F won't make a huge difference. It's worth noting that the Ilford chart is based on degrees Celsius and that the values given in Fahrenheit are rounded numbers. Yes, 20°C = 68°F, but 21°C = 69.8°F and 22°C = 71.6°F (not 72°F), etc.

However, if you want to be more precise than that, here are couple of suggestions.

Use the Ilford chart to come up with a factor for each degree Celsius, i.e., a value that you multiply the previous temperature by to arrive at the second. Then, convert this to F by using the good old 10°C = 18°F rule and then use that to determine how much you need to change development when the temperature varies by 1°F.

Alternately, if you can't heat your developer up to 75°F, you can cool it down to 71.6°F. Then just use the Ilford chart time for 22°C. I might try processing at a lower temperature anyway unless you're using a processor that simply won't go lower. B&w processes were designed for 20°C.

Or just use your usual time plus 5% and be done with it.

Best,

Doremus

Before I started using XTOL 1:1 i hated cooling chems. It is very unreliable.

Doremus Scudder · Jan 24, 2023

Radost said:
Before I started using XTOL 1:1 i hated cooling chems. It is very unreliable.

I agree, It seems you must be in a situation where the ambient temperature is quite high if your standard processing temperature is 75°F.

Developing at ambient temperature would seem to be best practice. That said, temperature drift upward during film development may not be as big an issue as you think. I did some tests years back when I was processing in the summer in Vienna in my not-air-conditioned apartment. Ambient temperature in the darkroom was 24°-25°C and I was processing at the standard 20°C in open trays and shuffling film by hand. In a 14-minute developing time, the increase in developer temperature from beginning to end of development was less than 1.5°C. I then just started at 20°C but used the adjusted time for 21°C as a rough mean temperature and did fine. Possibly a similar approach would work for you?

Doremus

Sirius Glass · Jan 24, 2023

Doremus Scudder said:
I agree, It seems you must be in a situation where the ambient temperature is quite high if your standard processing temperature is 75°F.

I would always prefer to develop at ambient temperature unless I had temperature control of some kind. That said, temperature drift upward during film development may not be as big an issue as you think. I did some tests years back when I was processing in the summer in Vienna in my not-air-conditioned apartment. Ambient temperature in the darkroom was 24°-25°C and I was processing at the standard 20°C in open trays and shuffling film by hand. In a 14-minute developing time, the increase in developer temperature from beginning to end of development was less than 1.5°C. I then just started at 20°C but used the adjusted time for 21°C as a rough mean temperature and did fine. Possibly a similar approach would work for you?

Doremus

I develop first thing in the morning or put on the air conditioning for a while.

Radost · Jan 24, 2023

faberryman said:
You could probably plot the relevant time and temperature information for your film and preferred contrast index from the Xtol datasheet on a sheet of graph paper and draw the curve connecting the dots in about five minutes. Put it in a page protector and save it for future use.

Can you elaborate?

Radost · Jan 24, 2023

Doremus Scudder said:
I agree, It seems you must be in a situation where the ambient temperature is quite high if your standard processing temperature is 75°F.

Developing at ambient temperature would seem to be best practice. That said, temperature drift upward during film development may not be as big an issue as you think. I did some tests years back when I was processing in the summer in Vienna in my not-air-conditioned apartment. Ambient temperature in the darkroom was 24°-25°C and I was processing at the standard 20°C in open trays and shuffling film by hand. In a 14-minute developing time, the increase in developer temperature from beginning to end of development was less than 1.5°C. I then just started at 20°C but used the adjusted time for 21°C as a rough mean temperature and did fine. Possibly a similar approach would work for you?

Doremus

Also I think 1:1 has better sharpness and tonality

Sirius Glass · Jan 24, 2023

Radost said:
Also I think 1:1 has better sharpness and tonality

Tonality, finer grain and better sharpness are improved with replenished XTOL over XTOL 1:1.

Radost · Jan 24, 2023

Sirius Glass said:
Tonality, finer grain and better sharpness are improved with replenished XTOL over XTOL 1:1.

I might try it but I only do 5-6 films a month.

Radost · Jan 24, 2023

Sirius Glass said:
Tonality, finer grain and better sharpness are improved with replenished XTOL over XTOL 1:1.

I might try it but I only do 5-6. I am afraid the seasoned replenished developer might die.

Radost · Jan 24, 2023

Also I am not clear how to adjust the time from fresh stock to replenished times “ which I was told are the same as 1:1.

Sirius Glass · Jan 24, 2023

Radost said:
I might try it but I only do 5-6. I am afraid the seasoned replenished developer might die.

Replenished XTOL infrequently used, such as I do, can last for years if it is tightly sealed from air.

Radost · Jan 24, 2023

Sirius Glass said:
Replenished XTOL infrequently used, such as I do, can last for years if it is tightly sealed from air.

And 2 liter working solution is better than 1 liter right?

Sirius Glass · Jan 24, 2023

Radost said:
And 2 liter working solution is better than 1 liter right?

What matters is the storage container. I use StopLossBagsTM www.stoplossbags.com

Radost · Jan 25, 2023

Sirius Glass said:
What matters is the storage container. I use StopLossBagsTM www.stoplossbags.com

stop loss bag is your replenisher?

A good temperature conversion table.

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