potassium bromide as anti-fog for negatives
I bought some old films that are likely to be fogged, or at least there is a risk of it, so I bought Photography Formulas potassium bromide.
It comes in crystals, and no instructions.
How much of it would you use and would you mix it with the developer - such as Rodinal 09 or Rodinal Special One shot.
I could weigh up the crystals let´s say 2 grams or 5 grams - how much water would you recommend - which dilution?
I haven't added it to existing B&W developer before, but I've added 10g/L to C-41 and processed at a 2 stop 'push' (4m 15s) and with 2 stops of overexposure before with good results.
How old is the film? You're going to need a test.
It's not usual to ad Potassium Bromide to film developers, it's unlikely to help much and you can print through any increased based fog. With papers adding bromide reduces the sensitivity meaning you need increased exposure.
In addition some film developers are very sensitive to increased bromide levels, it inhibits the action of Metol, it may well have a similar effect on the p-Aminophenol in Rodinal, but would have far less effect with Rodinal Special which is a PQ developer. Phenidone is restistant to much higher levels of Bromide.
Ian; you can lower the fog level in films with KBr, even if the fog level density is say 1.5, you can get it back down again.
which dev have you tried?
Originally Posted by Athiril
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C-41, E-6 first developer mostly. I've done random tests on B&W with own dev and seeing how much density I could pull down.
Originally Posted by Xmas
See here, this is the last one I've done - http://www.apug.org/forums/forum40/1...-e-6-film.html
If I can pull down fog hard on C-41 and E-6 (E-6 first dev is a B&W negative developer) then you can certainly do it on B&W film.
There is no correct value for Potassium Bromide addition in film developers, since your film is out of spec and nobody can know for sure how much is needed to get fog level back down. Fortunately you can find out the correct amount for your combination of film&developer with little effort:
- In complete darkness put a short, unexposed clip in your film tank. There is no need to put the clip on the spindle, but make sure you have that black tube in your tank in the correct position, or light will come into the tank through the lid.
- Take just as much developer as needed to completely immerse the test clip and do a test run with this setup. Stop, wash, fix, wash again, then inspect the test clip.
- If that first test clip is not significantly fogged, you can develop without any extra restrainer.
- If that first test clip is noticeably fogged, start with 2g/l Bromide and do the test again.
- If the second clip is still fogged, go up to 5g/l, if it is completely fog free, retry with 1 g/l. If there is only weak fog, you are fine with 2 g/l.
Since your film is fogged from old age and/or improper storage, there is no need to fine tune the amount of KBr, since there will be some variation between film rolls anyway. If you want perfect and reproducible results, use fresh film ...
PS: If Bromide had no effect on Phenidone based developers, then please someone explain me why they put it in E6 FD. And in Crawley's FX-37. And in ID-68 aka Microphen ...
Last edited by Rudeofus; 03-15-2014 at 07:35 AM. Click to view previous post history.
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I agree with Ian that using potassium bromide is not needed. In addition film losses speed with age and the bromide will also cause a loss of film speed. So not a good idea.
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KBr is a known anti fogging agent in edev formulaeas it buffers development,adding it toexisting formulae is likely to upset the fine balanceof ingredients and could impede development beyond your wishes.if you insist to try,I'd start with no more than 0.5g/land increase by the same amount until you get your desired result.good luck.
Originally Posted by Auroraua
Last edited by RalphLambrecht; 03-15-2014 at 01:03 PM. Click to view previous post history.
Originally Posted by Rudeofus
PQ developers are tolerant to much higher Bromide levels, this is because the Bromide doesn't suppress the activity of the Phenidonne but it does suppress the Metol in MQ developers.
This is particularly important where developers are replenished, Autophen a commercial PQ version of D76/ID-11 had far greater capacity and could be replenished by a topping up method rather than the bleed & top up needed with D76.ID-11.
So Bromide is more effective in a PQ developer as a restrainer without causing any speed loss hendce why it's used in the developers you mention.