I plan to develop 2 rolls of RPX 25 today. Inside the house it must be around 25 degrees C. What is the procedure for developing times when temperature is above 68 degrees F?
Developing Times for Hotter Days In Summer
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MattKing
Moderator
My starting point is to use the development dial in a Kodak Darkroom Dataguide.
I've seen some recent observations that, at least with the older dials (which relate to older films), it may be necessary to add a bit more time (10%) as you get higher than 24 C.
As long as development times stay longer than 5 minutes, there usually isn't any problem working around 25 C.
I've seen some recent observations that, at least with the older dials (which relate to older films), it may be necessary to add a bit more time (10%) as you get higher than 24 C.
As long as development times stay longer than 5 minutes, there usually isn't any problem working around 25 C.
OP
OP
Adding time as it gets hotter? I would think heat would reduce times, wouldn't it?
I’ve always adjusted by 4% per F degree. When I was in Florida, my cold water tap was always over 80F.
MattKing
Moderator
No - the times get shorter with higher temperatures. You need to be careful if the increase in temperature results in times less than 5 minutes.
The 10% increase was a reference to the fact that some have observed that the dials may recommend too short a time for the higher temperatures - perhaps due to the changes in films since the Dataguides were current.
My rule is to shorten developing time for increased temperature; 4% per degree F (which comes to 7% per degree C). Apply this as a power -- if you have a time for 20 C and can't get your solutions below 25 C, you'd divide your original time (say, 7 minutes) by 1.07 ^ 5 = 1.4m giving 4.9 minutes or 4:55 in this example starting time.
MattKing
Moderator
My 1970 Dataguide says that if 10 minutes works well at 68F, you should use 7' 15" at 75F.
The 1980 Dataguide says that if 10 minutes works well at 68F, you also should use 7' 15" at 75F.
I've reference degrees F because it is easier to read them on the 1970 dial. By 1980, degrees F and degrees C are equally easy to read.
The 1980 Dataguide says that if 10 minutes works well at 68F, you also should use 7' 15" at 75F.
I've reference degrees F because it is easier to read them on the 1970 dial. By 1980, degrees F and degrees C are equally easy to read.
MattKing
Moderator
The Dataguide dial would recommend 4:45 - so close to the same.
The advantage of my way is, if it comes to it, I have the conversion factor in my head and can do the arithmetic either mentally or with pencil and paper. No Dataguide needed (at least for this).
Those good old Darkroom Dataguides are like gold. Kodak, Ilford, Adox if you're listening here's a neat idea for an updated little cardstock computer I would pay 10 bucks for a nice one.
I occasionally use my little Jobo Duolab for a couple of rolls of film. It has 3 temperature settings, the lowest (24°C) was designed to accommodate both black and white films and Cibachrome. It works perfectly well with XTOL and Rodinal using manufacturer published times.
Modern films can be handled at warm temperatures thanks to the hardened emulsions right from the factory.
I occasionally use my little Jobo Duolab for a couple of rolls of film. It has 3 temperature settings, the lowest (24°C) was designed to accommodate both black and white films and Cibachrome. It works perfectly well with XTOL and Rodinal using manufacturer published times.
Modern films can be handled at warm temperatures thanks to the hardened emulsions right from the factory.
MattKing
Moderator
I am a visual learner 
Can you explain this in more detail, Donald. I think I can get to the 4.9 minutes except that I get 4.99 minutes but couldn't see where the 4.55 comes from. Thanks
pentaxuser
Last edited:
MattKing
Moderator
It's easy - for a 5 C difference, just raise 1.07 to the fifth power in your head and then divide the original development time by the result
.Personally, I'd do better with a calculator or some time with a pencil and paper.
From Ralph Lambrecht's book, Way Beyond Monochrome:
MattKing
Moderator
All of which methods seem to come to approximately the same result.
By the way, 4% corresponds to Ralph's temperature coefficient of 2.5.
By the way, 4% corresponds to Ralph's temperature coefficient of 2.5.
I got 4.9 minutes by mentally multiplying 0.7 (reciprocal of 1.4, approximately, which I happened to recognize from square root of two in geometry) by 7 -- and 0.9 minutes is 54 seconds, which become 4 min 55 (after rounding) seconds, notated in h:m:s form as 4:55.
And @MattKing I can do that (1.07 ^ 5) in my head, but I'd rather use a calculator if there's one handy (got one on every computer I use and one in my phone, should be set); if it were a number like 1.24 instead of 1.07, I'd probably stoop to writing it down without a calculator handy.
I use the Ilford compensation chart from the Ilford website,, I have downloaded and printed off some copies and ones lives on my darkroom wall
Andrew O'Neill
Moderator
Google Ilford time temperature chart. I use it. Seems to work well.
Thanks Donald. It may be that what I did was with a calculator so resulted in a difference of a few seconds. I couldn't do 1.07 to the power of 5 in my head to save my life. This was what I presume was 7% decrease in time per one degree centigrade over the 5 degrees Braxus mentioned. So this becomes 1.07 to the power of 5 which is 1.402551731 which as we are looking for a decrease from 7 minutes @ 20C means dividing the 7 by 1.402551731 which is 4.99 mins so as near as damn it 5 mins.
So I think we differ by 5 secs which is neither here nor there so why am I apparently labouring the point? It is simply that I want to be sure I have done the calculation the correct way and that our difference of 5 secs stems from this and not a misunderstanding of what you did in your original formula which, as long as I have used it correctly, I found to be a new and useful addition to my knowledge. Frankly before I saw your formula I resorted to Ralph's table which is very good but getting a small calculator out is easier and simpler than pulling Ralph's book out of the bookshelf. It is a weighty tome in terms of both heaviness and its superb content.
Other than simple arithmetic I have been nowhere near mathematical formulas for about 6 decades
Thanks
pentaxuser
OP
OP
Well my temperature for the developer was 27 degrees C. With that in Xtol 1:1 (normal time is 8 minutes), I got a little over 4 minutes with the temp. Rolls are done now and rinsing in the sink. I'll view them to see if the time looked correct.
You know what would be super cool. A iPad program that looks just like the Kodak dial. Thoroughly researched and developed by the MIT physics department, paid for by pandemic rescue money. 
I have the same film computer as Matt, the only current films listed are Tri-X and TXP. Developer choice is D-76. If you want to process Ektapan, Super XX, Royal Pan, or Panatomic X in Microdol-X or Polydol you'll be all set.
XTOL charts from Kodak, and Agfa's times for Rodinal get me through
I have the same film computer as Matt, the only current films listed are Tri-X and TXP. Developer choice is D-76. If you want to process Ektapan, Super XX, Royal Pan, or Panatomic X in Microdol-X or Polydol you'll be all set.
XTOL charts from Kodak, and Agfa's times for Rodinal get me through
This is what you get for living in paradise where you rarely need AC (or are too cheap to turn it on)
The Massive Development Chart app has a time/temperature feature.You know what would be super cool. A iPad program that looks just like the Kodak dial. Thoroughly researched and developed by the MIT physics department, paid for by pandemic rescue money.
I have the same film computer as Matt, the only current films listed are Tri-X and TXP. Developer choice is D-76. If you want to process Ektapan, Super XX, Royal Pan, or Panatomic X in Microdol-X or Polydol you'll be all set.
XTOL charts from Kodak, and Agfa's times for Rodinal get me through
MattKing
Moderator
Just use the dial to reverse engineer a development number for current films by locating the manufacturer's recommended 20C/68F developing time.
Even better, if you have your own favourite 20C/68F developing time, use it for the reverse engineering.
I add my own custom development numbers to the list of films using a sticky note.
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