C-41 bleach aeration

thornhill · Jun 8, 2006

Hello all.

I've got an aquarium bubble stone for aerating my fresh Flexicolor bleach. I'd like to know what would be the best amount of time to be running it. Five minutes before processing? An hour? I'm an amateur who only develops sporadically so I'd prefer to avoid running it 24/7. TIA, Derek

Ed Sukach · Jun 8, 2006

I'm lost. Does Flexicolor C-41 Bleach require aeration?

Claire Senft · Jun 8, 2006

If recall correctly C41 bleach can not be over aerated. It can be under aerated. I known nothing about the device you are using. I would imagine that if you bought a cheap electric mixer for cooking and dedicated it to using on your bleach and used for an 1/2 hour prior to procesing negatives that your bleach would be fully aerated. Build yourself a little stand to hold the mixer and use a container that is suitable and find an appropriate speed leave her rip.

Nick Zentena · Jun 8, 2006

I think it depends on how you process. In something like a Jobo that rotates all the time air is being forced in the whole time. If you're hand inverting I'd expect a greater need to aerate.

Photo Engineer · Jun 8, 2006

A popular misconception is that aeration regenerates the bleach.

It does, but does not replenish the used chemistry and so it still goes down in activity.

Placing 1/2 liter in a 1 liter jar, capping it firmly and shaking it for a minute or two will usually do the job, but to what purpose if you also need to rebalance the pH and add more NaBr and Sulfite?

PE

Lopaka · Jun 8, 2006

I think I'm still slightly confused.

Kodak's publication Z131_3 on C-41 batch processing states: 'For efficient bleaching, you must aerate the bleach.' However, the paragraph explaining this is contained in the section on sink-line processing. Further down, in the section on rotary-tube processing with Bleach III, it does not repeat a discussion of aeration.

So is the standard continuous back-and-forth rotation in the JOBO sufficient to bleach properly?

Bob

Photo Engineer · Jun 8, 2006

The Jobo will aerate the bleach, a sink line process with nitrogen burst agitation or manual agitation will not aerate the bleach.

But, see my post above about replenishing the bleach. That is also necessary.

PE

gordrob · Jun 8, 2006

Photo Engineer said:
The Jobo will aerate the bleach, a sink line process with nitrogen burst agitation or manual agitation will not aerate the bleach.

PE

In a sink line process what does the nitrogen burst do? When processing E6 I had a magenta cast on the final 4x5 transparency and was told that it was due to not having aerated the bleach when the transparency was in the bleach. So what does one have to do in regards to agitation when the film is in the bleach for either C41 or E6

Thanks
Gord

Photo Engineer · Jun 8, 2006

Gord;

The bleach should be all in the ferric form (Ferric Ammonium EDTA) or the equivalent complex in the new Bleach III. If it is in the Ferrous form, then it will not bleach. Air is sufficient to oxidize ferrous salts to ferric.

The aeration methods referred to above, posted on the EK web site will work with the sink line process, because the nitrogen bursts purge the bleach of all excess air, so just making sure that there is air agitated through the bleach as described by EK will fix the problem.

THe magenta cast problem has been fixed. E6 films and C41 films from years ago would form cyan leuco dye in the presence of ferrous ion and if the pH became too acid. Kodak fixed it years ago. But, these slides or negatives can be 'restored' by bleaching in a ferricyanide bleach bath, wash, then stabilze.

With modern films, the only problem with ferrous ion is that the bleach will be too weak to remove (bleach) all of the silver to silver halide. Then you get silver retention.

Oxidation and replenishment are needed with used bleach. Oxidation keeps the ferric salt level high enough to remove silver, and replenishment brings the bromide, sulfite and acid level to the right values.

PE

srs5694 · Jun 8, 2006

Photo Engineer said:
Oxidation and replenishment are needed with used bleach. Oxidation keeps the ferric salt level high enough to remove silver, and replenishment brings the bromide, sulfite and acid level to the right values.

So is aeration of bleach necessary with fresh bleach (straight out of the bottle), or only with used (and possibly replenished) bleach? I've been assuming it's always necessary, and so have been shaking my bleach even when it's fresh, but if that's unnecessary I'll save myself some wrist action with fresh bleach.

Photo Engineer · Jun 8, 2006

Aeration of fresh bleach is probably not needed, as the aeration in tap water and the mixing action may do the trick, but the new bleach III is premixed. Distilled water has had most all of the air driven out of it by the distillation process.

IDK what sitting on the shelf for months may do to the concentrate other than form crystals. So, the shaking does not hurt.

If you use a Jobo though, the aeration from the agitation will completely aerate a batch of bleach.

BTW, aeration is not suggested for blixes. It can hurt the thiosulfate by oxidizing it. It also oxidizes the sulfite in blixes and bleaches which contain it.

PE

gordrob · Jun 9, 2006

Thanks PE for the explanation of the areation of the bleach and perhaps I will be able to salvage a couple of old transparencies.

Gord

C-41 bleach aeration

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