Printout revisited

Silverhalide Emulsions / Chemistry.
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Printout revisited

Post by jrburns47 »

Reading up again on using 2.5gms of KI in a liter distilled water solution as a printout preventer. It’s recommended as being the very last step before drying.

I’m using a Nick’s #5 for Agfa catechol developer w/ an FeEDTA bleach, followed by filtered water wash, followed by 4 step ethyl alcohol graded drying method and into drying cabinet (8E75HD plate). The alcohol steps are 50/50, 75/25, 90/10, and a “pure” ethyl spray. Getting very good results. However, not using potassium iodide printout prevention step.

What do you chemists out there think about mixing the potassium iodide w/ pure ethyl alcohol in a tray as a final step after the 90/10 step instead of mixing the KI w/ distilled water.

I would try it without asking for guidance but the pure ethyl is so damned expensive these days here in the US that I’m reluctant to waste a half liter if it’s a bad idea.
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Re: Printout revisited

Post by Din »

The solubility of potassium iodide in ethyl alcohol decreases as the concentration of ethyl alcohol increases*. Since the way the iodide reduces printout is by replacement of the bromide ion in emulsions with the iodide ion, the large number of bromide ions still in the emulsion (depending, of course, on the number of grains that have not been reduced), means you'd need quite a large amount of ethyl alcohol to dissolve sufficient potassium iodide. This may be counter-productive to the aim of reducing cost.

It's possible to calculate it all out, but I suggest you try it out first. I'd cut an exposed and developed plate in half, and use your method on one half. I'd put both halves under a bank of fluorescent lights (fluorescent because there's more blue in the spectrum), and examine both halves after, say, three/four hours. An even more objective test would be to illuminate both halves to laser light, and take a reading of the intensity of the light after passing through the plates. If successful, the intensity of one half, say I(1), of the printed out half would be less than the intensity of the other half, say I(2). Then, the amount of printout, P, is given by

P = {(I(2) - I(1)}/I(1).

* ... V/abstract
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Re: Printout revisited

Post by Martin »

I'd guess with ethanol it takes quite some time for the KI to diffuse into the emulsion - methanol would be much faster. Maybe you could even use a methanol/KI bath after your ethanol deyhdration steps.The big question though is if the process of converting AgBr into AgI does require at least a bit of water...

As for converting silver bromide to silver iodide, noise might be OK as long as you use very fine grained emulsions and red exposures. I remember increased noise on Agfa and Ilford but not on PFG-03.
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Re: Printout revisited

Post by BobH »

I'd recommend a KI in water bath before the drying steps. You're replacing the bromide as Dinesh mentions, and that won't be affected by the subsequent graded alcohol baths. All the alcohol baths do is dissolve the water out of the emulsion, and replace it with a faster evaporating liquid. There's really no need for the KI to be in the final, final bath.
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