Originally Posted by
LabRat
If you ever developed a sheet of ortho film in a tray under safelight, you have seen a cloud of a fuzzy beard over heavily exposed areas... This "cloud" contains a combination of superaddivate components (that increase development) and bromide & by-products that inhibit development... Agitation moves these back into the solution to normally average out development...
Now, a developing tank is a confined space with support ribs to hold film, and film near other film etc... The "clouds" can easily drift over to other film areas where their "effect" can be easily seen (like skies, edges etc), so normal ideal agitation involves getting these "clouds" away from the films back into the solution... Too little, and the clouds remain near film, too much, and the surging of solutions can band them together (like a river) over one area and leave trails...
"Clouds" are more dense in less diluted developers due to more local development action, but less dense in more diluted solutions so in the confines of a tank, it will be easier to diffuse the thinner clouds more diluted...
Stand and semi-stand processing depend on less clouding and usually vertical placement while processing, where gravity assists the clouds to roll off areas and diffuse back into solution (hopefully)... As mentioned, film and supports can impede this process, so design of the tank is important... And method of agitation (not too little/not too much) is crucial for success... Follow the tank's manufacturers directions carefully for a starting point...
As a general point, agitation methods that allow tank to be inverted during agitation help a lot...
Steve K
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