Did I kill my bleach?

siguii · Sep 17, 2014

So, I was trying to make C41 bleach. I dissolved some KBr in water and added Ferric-ammonium EDTA solution. Then I started adding acetic acid to lower the pH to the recommended 6.5. But I accidentally added too much and now the pH looks to be about 5. The solution turned from opaque brown to dark red. Is it dead, or will it work if I raise the pH somehow? Would baking soda work? It's the only alkali I have on hand.

Photo Engineer · Sep 17, 2014

It will probably be just fine. Depending on version, it should be dark red. The brown color is not good.

PE

siguii · Sep 17, 2014

Yeah, actually now comparing it to my old bottle of blix, I think it was just my imagination that it changed color.

So I shouldn't add anything to raise the pH?

Edit: never mind, seems I misread the pH test chart. It actually seems to be about right.

Anyway, is 11g of KBr to 1 pint of bleach a good amount?

Rudeofus · Sep 17, 2014

11 g per pint will work, but your bleach will exhaust quickly. Look (there was a url link here which no longer exists) for the recipe of a standard E6 bleach based on Ammonium Ferric EDTA and Potassium Bromide. You can safely leave out the Ammonium Nitrate, and the bleach will work just as well for C-41.

Note, that the Ammonium Ferric EDTA used to oxidize the Silver will be restored by aerial Oxygen, whereas the Bromide tied up as AgBr will be gone. The more Bromide you add the longer your bleach will last.

PS: Your bleach will be more active at pH 5.0 than at pH 6.5, so pH 5.0 would actually be a good thing. Since there will be a fixer bath at pH 6.5 afterwards, your colors should come out fine regardless of bleach pH.

siguii · Sep 17, 2014

Thanks for the info. I'll increase the amount of bromide. Just curious, what purpose does the nitrate component of the E6 bleach serve? I have some potassium nitrate which I could add if it will do anything.

Rudeofus · Sep 17, 2014

Nitrate supposedly preserves stainless steel tanks from corrosion by the bleach. These commercial bleaches were designed for continuous replenished processing, and these outfits had different requirements than us plastic inversion tank folks. Since Nitrate has uses outside the photographic realm that have raised concerns with authorities, it is hard to obtain in some regions. Luckily we don't really need it ...

siguii · Sep 17, 2014

I do all my developing in a stainless steel Nikor tank. So in that case, should I add nitrate?

Photo Engineer · Sep 17, 2014

If you leave your bleach in the tank overnight or for a few days, the answer is yes, otherwise no.

PE

Did I kill my bleach?

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