agitation among the frogs about developers. since photography is something we do in the dark, maybe we can improve our work by knowing more of the secret. craft sometimes hides the meaning. the means get in the way. the camera blocks your view of the world.
The mechanisms of developing film (and paper) have been studied more than a century. The researchers provided products and procedures that employed hundreds of thousands over the 20th century. Some of that foundation work lead to our current digital imaging systems. Strange enough, even to enhanced solar cells and window coverings. So, it would seem a good place to look for a journey through the chemical photolab would be the manufacturers’ instructions and references. The things they read and wrote. It isn’t what most do. The information seems too curt, or too complex, so what happens is a large industry of writers, workshops and guide books flourish. Much of that has moved to youtube, and online chat forums — advice is given, repeated, overheard, rephrased — turning into accepted practice. They want to be influencers; they want to be remembered, so, they gossip. Repeat what others may have meant. It can’t hurt, can it.
A phrase I used in my teaching days: Read the directions twice; try them at least once before asking someone what they do.
Box Speed. Box Developer — that’s another. Every emulsion is tested. The chemists use developer during design and development of the film. Also, every chemist agitates the film in the developer. So, over the years they learned from the large users of their products what features would prove most useful.
There are many effects, some say defects, that are a result of developer composition and agitation. One film is not all film.
Mackie line, Eberhard effect, Kostinsky effect. 
“Development in a vertical tank without agitation, or with grossly inadequate agitation, may produce streaks.”
 “Forcing development with concnetrated metol-hydroquingoe, metol-chlorohydroquinone, or catechol developers results in somewhat higher effective emulsion speeds but only when the fog values become fairly considerable.”
“Active developer diffusing from areas of low to high exposure will cause increased development of the boudndary of the image, producing increase contour desnity but also increasing teh size of the silver grains in the enhanced edge density … conventional fine-grain developers , such as Kodak Developer D-767, are diluted with water to form the dilute developing solution that gives increase image edge effects…”
The emulsion is three dimensional — more like a sponge than a ‘film.’ The further from the center is the edge, that is, the bigger the film, the greater the possible difference with agitation. Color processing requires known diffusion rates of the residue of developing — change that and you change the resultant hue-set. Not a cross-over, once again: not a cross-over. A hue shift isn’t a shift in gamma ratios.
- E. R. Bullock.
- J. Rzymkowski.