From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 02/03/01-10:56:45 PM Z
At 11:53 PM 02/03/2001 -0400, you wrote:
>Richard Knoppow wrote:
>
>> I use Unidrums and a Bessler drum for large format negatives. I have a
>>reversing Unidrum roller. They do a good job but I discovered I was getting
>>bromide streaks at very dense highlights on either side in the direction or
>>rotation. Evidently there is not enough turbulence to move the developer
>>sideways, so the reaction products keep being swept back and forth along
>>the same path. The cure is to agitate the drum sideways occasionally, or to
>>roll it manually with some irregularity.
>
>When using the drum on a motor base I agitate sideways vigorously once
>every 2-3 minutes and have not seen any sign of bromide drag.
>
>I have some questions about bromide drag. Is it worse with certain
>developers or classes of developers and/or is it affected by dilution, or
>is it caused uniquely by the type of agitation?
>
>Sandy King
>
>
This is about what I do. I think this is mainly a result of the type of
agitation, however, the effect of developer reaction products varies with
the developer. Some developers, Metol for example, have reaction products
which suppress development, others, Hydroquinone for example, have reaction
products which accelerate development or are active developers themselves
(Quinones). This last is one reason that Hydroquinone is used for very high
contrast developers. Superadditive combinations like Metol and Hydroquinone
tend to have reaction products which are converted back into active
developers of about the same activity as the original. Also, some
developers are more sentive to bromide than others. Metol is relatively
insensitive, hydroquinone very sensitive, Phenidone almost insensitive
(which is why Benzotriazole is used a restrainer with it). The amount of
sulfite is also a factor. Sulfite tends to prevent the formation of
oxidation products of development products. Thats why high sulfite
developers don't form border effects nearly as readily as low sulfite ones
do, and why they are relatively free from staining. Diluted developers
generally have little sulfite in them so they are more subject to oxidation
and to the effects of reaction products on development.
Drum developing usually combines a relatively small amount of developer
with conditions which tend towards rapid oxidation, i.e., a thin layer of
developer over the film or paper, plus lots of surface exposed to the air.
I think the main reason for directional effects is simply that the
reaction products are not very effectively carried away from the site of
high density areas where the developer is being oxidized at a more rapid
rate.
Directional effects in motion picture processing machines were a plague
at one time, especially for development of sound tracks, where the effect
results in severe distortion.
In my case, I noted the effect first on 8x10 negatives of a city scape
with strong direct sunlight reflected from windows. There were dark streaks
from the highlights on the print along the line of rotation. This was
observed with APX-100 processed in Rodinal 1:50.
I've gotten similar effects using Plus-X and Rodinal but less so with
D-76. Sideways agitation cures it.
If you start to look for irregular development you can find it with
nearly every method of development. Even brush development, long used for
sensitometric research, is not completely uniform.
BTW, modern motion picture machines use spray applicaton of processing
solutions and sound tracks are developed by applicaton of viscous developer
solutions. The sound tracks must be silver rather than dye so the edges
have to be redeveloped. This was a cause for lots of bad sound, especially
around the 1970's and 80's when no one seemed to be paying any attention.
---- Richard Knoppow Los Angeles,Ca. dickburk@ix.netcom.com
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