Agitation
The periodic movement of the developing tank that replenishes fresh chemistry at the emulsion surface.
Measured in
seconds per interval
In depth
Without agitation, developer next to the emulsion exhausts and by-products sink downward, producing streaks below dense areas. Too much agitation raises contrast and can cause surge marks near the sprocket holes. Because the standard development times published by manufacturers assume a specific pattern, changing agitation changes contrast as surely as changing time does.
Examples in practice
Inverting the tank four times every minute is a common standard; agitating continuously would raise contrast noticeably.