Originally Posted by
nbagno
This is from Jobo's 2020 calendar "Pre-Wash
In this context it is helpful to remark that JOBO clearly recommends to always pre-wash
your film (and paper) in rotary processing for 2 to 5 minutes. Pre-washing allows the
emulsion to soften up and absorb first water molecules. Keep in mind that, different from
inversion processing, in rotary processing chemistry does not hit the whole film surface
at once. Pre-washing makes sure that chemical is evenly absorbed by the emulsion in
rotary processing of your film (and paper), avoiding unevenness and undulations on the
film surface. Our service department found that 99% of customer complaints with unevenness were strictly correlated to the lack of pre-wash. Color-processing times remain
unchanged even with pre-wash, whilst B&W development times need to be increased by
an average of 20% compared to B&W development without pre-wash.
With inversion processing the pre-wash can be skipped as the whole film is always simultaneously immersed in chemistry. Due to the reduced agitation in comparison to rotary
processing the development times are about 25% longer for inversion processing than
they are for rotary processing to achieve the same density. As a rule of thumb, you can
say that developing film in rotary processing with pre-wash will take about the same time
as inversion processing without pre-wash at any given temperature. Most large format
photographers know about the challenge of achieving evenness of processing when working manually. The larger the film format the greater this challenge becomes. Apart from
perfect control of push & pull process, the evenness is one of the main reasons why a
large format photographer should opt for the JOBO processor with Expert Drum."
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