BW Film Development Time by Temperature

B&W Film Development Time vs. Temperature

Temperature has a big say in how black-and-white developers behave. Warm chemistry works faster, cool chemistry drags. A linear approximation that gets a lot of use is t_new = t_base × (1 − 0.07 × (T − 20)): every degree above the 20°C reference shaves about 7% off the time. Once you stray far from that reference, the Ilford/Kodak compensation chart, which follows an Arrhenius-style curve, will give you better numbers.

At 20°C / 68°F the usual reference times for a typical 400-speed film land around 9 minutes for Kodak D-76 stock and 8 minutes for Ilford ID-11 stock. Agitate 5 seconds out of every 30 and you keep development even, with none of the surge marks you get from neglecting the tank. A 30-second water pre-soak brings the film up to temperature and cuts down on air bells. When you need a specific combination, the Massive Dev Chart database (digitaltruth.com) covers thousands of film and developer pairings, and most film photographers treat it as the go-to.

Applications

Home developers and people sharing a darkroom lean on this, as do photo schools running students through the wet process. Photojournalist archives use it while restoring old negatives, and lab techs reach for it when the chemistry drifts away from 20°C over a long session and the times need adjusting.

FAQ

What if my developer is at 24°C? Multiply the base time by (1 − 0.07×4) = 0.72, so an 8-minute time drops to about 5:45. Below 18°C the linear rule stops holding up, so switch to the Massive Dev Chart factors instead.

Why 5s every 30s agitation? That cadence comes from Kodak’s D-76 recommendation. It moves enough fresh developer across the emulsion surface while staying gentle enough to keep bromide from streaking down past the sprocket holes.

Should I pre-soak? A 30-second pre-soak in water at developer temperature knocks out air bubbles and steadies the temperature before you start. You can skip it, but for sheet film it’s worth doing.