Halide ions & other byproduct's effect on developer

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andynguyen
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Joined: Wed Feb 24, 2016 8:45 pm

Halide ions & other byproduct's effect on developer

Post by andynguyen »

I dont know who else to ask, so here goes:



As most of us knows, halide ions are generated as developer reacts with silver halide on the film surface. & bromide, in particular, is a restrainer. As I test developer mix only using 6-7 135 frames, I start to wonder: would the film surface vs developer volume ratio has a significant effect on developer action?



Lemme elaborate: even if one uses, say, 500ml of developer for a roll of film, which exceeds the minimum amount required, the by-product given off during reaction, particularly during the 1st minute of continuous agitation has a subsequent restraining effect on the reaction. So 1 whole roll would give off more restrainer than, say, 10 frames. Would this be significant enough to cause different development result?



In case one wonders why I'd be concerned with this trivia when I can simply shoot the whole roll instead, then i'd say that my concern, once generalized, applies to other scenario as well. For example: would it be the same to dev 2 sheets of 4x5 vs 12 sheets in the same tank using the same volume of dev. Now that's probably more realistic for consideration?



Is there any figures or previous experiment regarding this?



On a side note: I noticed in formula such as Pyrocat-HD, there is KBr in minute amount. I understand that this is to prevent fogging. My question is: how much is this amount compared to the amount released by the average roll of film?
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sanchell
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Halide ions & other byproduct's effect on developer

Post by sanchell »

You are 100% correct that the bromide precipitated into the developing solution does have a restraining effect. The amount of bromide is greater with a 36 exposure roll, or 4 sheets of 4x5, than with a partial roll or 1-2 sheets of 4x5. This is one of the reasons it is important to use more developer than the bare minimum you can get away with. When excess developer is used, whether with one sheet or 4 sheets, the amount of bromide precipitated into solution is negligible, when measured as a percentage of the solution. When minimum developer is used (250ml per 8x10 sq in of film surface) then the percentage of bromide can have a noticeable restraining effect.



I have one rule in my darkroom practice: get the best doggone negative possible. I would rather use fifty cents more worth of developer than have a single underdeveloped negative.
Do it in the Dark,



Steve Anchell
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