As we are going to make our next emulsion experiment very soon (after a long pause), some thoughts have arisen concerning washing and fogging.

My understanding about latent image may be a bit incomplete, but I'm presuming that single metallic Ag atoms work as development sites and without them there is no latent image and thus no fog.

Basically, I can understand that overwashing causes the bromide level to go too low and that a bit of extra bromide salt is needed to avoid fogging. Is this because extra bromide can prevent Ag from reducing from AgBr, or even by reacting with reduced Ag to form AgBr again?

Then, what are the concequences of underwashing? Is it just problem with adhesion to film base because of the salts precipitating when drying? Or is there something else? Can underwashing also cause fogging? As I see it, IMO fog is quite an evil enemy, so I'd rather under- than overwash. Does this make sense?

Well, then, about the washing. If it's just the bromide level that has to remain at a certain level, and other products (like NO3 ions) can be safely washed completely out, wouldn't it be a good idea to add a tad of NaBr to wash water? As long as the noodles have higher bromide, diffusion would work quite the same way as with pure water (well a bit slower). But as bromide goes lower in emulsion, a low level of bromide in water would stop the diffusion at the desired point. Washing of other salts would continue, though. Is this sensible at all?

If this is correct, I would guess that adding between 0.029 and 0.192 g/l NaBr to the wash water (maybe after the initial 0.5 hour that is safe anyway without the bromide) would be a great thing to do as a guarantee against
overwashing. The above-mentioned figures was calculated by PE for me when I asked about adding bromide to an already overwashed emulsion. But now, I would be adding it to wash water beforehand. It would go into the emulsion by diffusion if already overwashed, or just prevent the overwashing by stopping the diffusion at the desired level.

Q#3, could ferricyanide+bromide bleach be used to remove any latent image / fog (convert any silver atoms to AgBr)?


Thanks.