Reuse C-41 Bleach

Bleach is the most expensive component in C-41 chemicals. But

theoretically it is never really exhausted. I dug out my collection

of Creative Darkroom Techniques magazine and located an article

written by Dr. Robert Chapman talking about reuse of C-41 bleach

indefinitely. Yes, you read it correctly. It is reuse C-41 bleach

indefinitely.

The article said by introducing a brief wash between color development

and bleach it is possible to prevent most of the carry over of the

developer into the bleach. As a result with proper aeration to restore

oxygen and occasional PH adjustment the bleach can be reused

indefinitely. Dr. Chapman claimed to have reused his 1 liter bleach

for over a year.

I understand bleach is critical to the result of C-41 process.

I often got grainy negatives becuase of bad bleach. My question is

is this realistic? I have a PH meter with a working probe. I have

discovered an economical way of calibrating it and keep it

calibrated. It is really tempting to give it a try. It can be

very easy by using a JOBO processor adding a 10 second wash between

color development and bleach. I probably want to reduce color

development by 5 seconds or so.

What do you experts say about this idea? If it works for a year

I will be more than happy to dump it. It also puts my PH meter to

use.

Nonsense! Bleach is an oxidizer, and is depleted through use. pH is a factor in its effectiveness, but restoring the pH will not renew the oxidizing capacity.

Chemistry 101 (102 maybe).

Dave;

I have put up several long posts on this very subject. I hope you have read them.

Basically, the FeEDTA is reduced, the sulfite is used up, and the bromide is used up. This gradually slows down bleaching until it stops.

It has a LOT of excess capacity, but you have to re-oxidize it, add more sulfite, and add more bromide. pH has little to do with this. Chapman did not come up with a miracle answer to this problem.

The answer is to extend time in the bleach as recommended, and / or replenish bleach with fresh bleach after every use.

I too have used bleach for months, but I keep increasing time, and eventually add fresh bleach to my working solution.

Ron Mowrey

Why not replenish? If you buy your bleach in larger bottles the cost per roll shouldn't be much of an issue.

Or you could mix up your own bleach.

Ron, I did read your posts. At one point I even thought I had believed

in something that was wrong. But when I dug out the magazine and read

the article again (I read it many yers ago) I began to wonder again.

I think this is a good subject to further discuss, whether I am wrong

or not.

The article was published on Darkroom and Creative Camera Techniques

by Dr. Robert Chapman who holds a chemistry PHD from Yale University.

The article was "C-41 Rinse Saves Bleach". Under the subject said " Making Bleach Last a Year or More". In the article basically it

added a brief 10 to 15 second rinse after color development to reduce

developer carrying over to bleach hence made bleach lasting a very

long time with occassional PH adjustment. Aeration of course was

needed between (before) each use of the bleach.

Dr. Robert Chapman also wrote articles on the magazine on ealier

publications about the C-41 process. I dug out that publication and

found the following about C-41 processing.

Color Development Reaction:

Step1: AgBr+DA->Ag+Br(-)+DA*

Step2: DA*+Ci->DA-Ci

Bleach Reaction:

Ag+Br(-)+FeEDTA(-)->AgBr+FeEDTA(-2)

DA is color development agent. Ci is CMY color couplers.

I think the Bromide in the bleach is never exhausted. It is provided

from the film when it is developed. The FeEDTA(-2) is regenerated back

to FeEDTA(-) by aeration so it is never exhausted either. In the

reaction equations I do not see sulfite being used. The bleach

formula in the article does not contain sulfite. It contains acetic

acid, sodium nitrate, EDTA and Ammonium bromide.

However, developer carry over is not completely stopped by a 10 second

rinse so the bleach needs PH adjustment occassionally and eventually

the bleach will go bad after a year or so.

I actually tried the idea myself and had some success untill I got

sloppy and skipped the rinse. Then everything turned upside down.

I think I was able to reuse 500ml of bleach for a dozen or so of

processing. I did not use my PH meter (too much work) to adjust

PH. I think I had limitted success because of skipping rinse and

had no accurate PH adjustment.

Kodak used to have a bleach 'regeneration' kit for doing such along with replenisher. I still remember that smell vividly.

During regeneration I'd aerate my bleach stock tank for about an hour with the mixer, and pump it back. All was well.

Dave;

I too have Dr Chapman's article. Unfortunately, the fact that the C41 bleach has a lot of excess capacity, and the fact that you can regenerate it by oxygenation masks the fact that it can become depeleted in sulfite and bromide.

The reactions in the developer are.

AgX + CD + NaCO3 -> Ag + NaX + CDox (simplified of course)

X = halide which remains in the developer solution.

In the bleach.

Ag + Fe(ic)EDTA + NH4Br -> AgX + Fe(ous)EDTA using up the halide in the bleach. (not balanced and omitting ammonium ion in the right side as this becomes quite complex (pun intended for all you chemists out there)

Sulfite in the bleach is also present to minimize stain due to developer carryover.

The bleach is very well buffered so pH is not a problem. The problem is consumption of 3 active ingredients, Ferric ion, bromide ion, and sulfite ion, all of which are present in very high concentration to speed the reaction.

I'm sorry, but this is a fact of chemistry. You can regenerate or replenish, but the inevitable happens. You run out of sulfite and bromide and bleaching slows or stops while stain goes up.

Ron Mowrey

"X = halide which remains in the developer solution."

Ron, you are right. This is why the bromide in the bleach is consumed.

To regenerate bleach some replenisher is required.

Thank you for the excellent info. I will toss out the idea of reusing

bleach. Darn, guess more money will go to Kodak now. Well it's a good

trade off. I do like Kodak to stay healthy and continue to supply good

products if the little money I contribute really helps.

Dave;

You can reuse bleach. It has a lot of capacity.

Just make sure it is oxidized well and that you increase time gradually as it is used. If you use it a lot, then just add some new bleach to the old, by taking out 50 - 100 ml / liter and adding fresh mixed bleach.

You just cannot keep using it by reoxidizing it. And, developer carryover is not all that bad if you oxidize the bleach, replensish from time to time, and increase time if needed.

Ron Mowrey

For some reason my last post is missing. I'll try it again.

Good to know that I can still reuse a bit of C-41 bleach. Thanks again, Ron, for your replies to this thread.

Dave;

You are quite welcome. Any time I can help, just e-mail me or post something.

Ron Mowrey

I humbly suggest downloading the C-41 and RA-4 Z manuals from the Kodak website. They have pretty much perfected the process. The manuals are explicit and very well written.

BTW, C-41 was developed for continuous use. Be sure to get information on small lab use. Bleach replenisher use should be very minimal, even with sporadic use.