Why 68 degrees?

Question:Why when processing film or printing a negative should the developer be 68 degrees? what happens when the temperature is hotter or colder?

Best Answer - Chosen by Asker: Why when processing film or printing a negative should the developer be 68 degrees? what happens when the temperature is hotter or colder?

Every chemical reaction has an optimal temperature, which affects the reaction speed. Film just happens to be formulated to work best at 68°. If you use a different temperature, as you know, you just alter the times. Within reason, this will still give satisfactory results, but if you go to high (like over 75°), you will start to see more grain. Go higher than that and you will actually start to see damage to the emulsion in the film that wil show up as white or light color blotches on the negatives where the emulsion layer has separated. If you go colder, you won't risk this kind of damage. As far as I know, you will only slow the process down. This can give a finer grain pattern with some films and sometimes you might do this intentionally. When I was pushing Tri-X to the limits and beyond (ASA/ISO 6400 plus), I'd cool the solutions before use and dilute the developer 1:4 (maybe more - I forget) to really slow the process down so the film wouldn't be excessively grainy. I was developing for 15-20 minutes sometimes...

Ryan makes an excellent point about uniform temperatures among ALL of your solutions, too.

it is said to be true temp of room temp

I never heard of 68 degrees! All depends on the 'country', 'location', 'environment', 'the labs positions' etc.

68 degrees is the recommended temperature for the given time. You can use other temperatures, and other times. Negatives will develop faster with higher temperatures, and slower at lower temperatures. Follow the chart!

you need to figure out what type of film you have. that will determine how long, and at what temperature, the reason this is true is because when putting in the developer, it is such a strong chemical that is needs to be diluted, and if it isn't at the right temp. it will not properly develop the silver-nitrate, etc. in the film. and when you are water rinsing it, you need to make sure it isnt too hott or cold, and at the SAME TEMP. as when you were developing it.. as to not weaken the film(hot) or make it cold... a degree or two isnt bad, because of an inconsistant water pressure and temp stabilizer, at my school, the temp changes often, and has gotten up to 5 degrees too much... but dont make it a habit.