Richard Knoppow (dickburk@ix.netcom.com)
Wed, 06 Oct 1999 11:43:29 -0700
At 11:01 AM 10/06/1999 +0200, you wrote:
>Bromide drag?
>
>This is a slightly off-topic question concerning processing of lith film
>for continuous in-camera negatives.
>
>I have used the LC1 developer, formulated by Dave Soemarko in PF #2 (a low
>on metol and HQ developer, high on sulphite, using acidic bisulphite to
>tame the lith film) and adapted it for in-camera negatives. I have used
>Freestyles APH lith film. My tests resulted in quite nice continuous tone
>negatives (at the expensive of film speed, I use 1 or 1.5 ASA...), when I
>used the following ratios: (A:B:water) 2:3:5
>
>Which is per litre (end concentrations):
>0.6 gr. Metol
>12 gr sodium sulphite
>0.6 gr. Hydroxyquinone
>3 gr. sodium bisulphite
>
>I used a JOBO processor with a print drum with special plastic inserts;
>these inserts make it possible for the developer to "reach" the back of
>the film, they also cause a lot of turbulence judging from the foam on top
>of the discarded solutions. For 2 sheets of 18 * 24 cm (7*9.5 inch) I use
>500ml of developer.
>
>The first series of negatives were quite promising, and printed nicely as
>silver gelatine contacts when using a grade O filter, they also printed ok
>as Kallitypes, but they could use some extra contrast/density (which isn't
>really a problem with Lith film..;-)..).
>
>My problem arouse when I made a further series: a couple of images with a
>lot of clear empty skies with flagpoles, a lamppost etc. All these objects
>exhibited a "smear"going up into the sky; a smear of added density on the
>negative; lighter when printed. I vaguely remember something about bromide
>drag; but I do not know what this exactly is.
>
>How is this caused, how do you recognize it, and how can I avoid it? I
>also thought this has something to do with exhaustion of the developer
>(not unlikely maybe), but why is this only happening on places where dark
>objects are next to light objects. I mean the JOBO is continuously mixing
>the developer.
>
>Any feedback appreciated
>
>Cor Breukel
>http://ruly70.medfac.leidenuniv.nl/~cor/cor.html
>
>
This is the opposite of bromide drag which leaves a streak of lower
density in the vicinity of high density areas of the image. Its a
directional effect when the film is moved either in one direction, as in
film processing machines, or back and forth as in a drum processor. If
there isn't enough turbulance to agitate the reaction products of
devlopment away they will continue to be dragged back and forth along a
line with the high density area that caused the reaction products.
The reaction products of development can also accellerate development as
well as restrain it. Which happens depends on the formula. The above
formula is a sort of highly diluted D-76 with some bisulfite buffering
which lowers the already low pH. Not a very active developer. With a
mixture of Metol and Hydroquinone its possible to have the accelerating
reaction products. I am not a good enough photo chemist to say for certain
but it certainly seems to be happening here.
I've encountered bromide drag with drums on electric rotators. The cure
was to agitate more slowly by hand and to rock the drum sideways frequently
to wash the reaction products away from the straight path they otherwise take.
This is a problem which was discovered a very long time ago when the
motion picture industry first started to use automatic processing machines.
It is also sometimes called "directional effect".
----
Richard Knoppow
Los Angeles,Ca.
dickburk@ix.netcom.com
This archive was generated by hypermail 2.0b3 on Fri Nov 05 1999 - 21:26:27