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# Thread: How accurate is using time to compensate for temp?

1. 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.

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

3. [QUOTE=ITD;628647]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.

4. Originally Posted by ITD
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?

5. 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.

6. Originally Posted by ITD
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.

7. Originally Posted by David William White
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...

8. Originally Posted by df cardwell
You can rely on Kodak's published info.
D76 is the gold standard.
That's good to hear, thanks.

9. 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

10. 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.

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