Which bleach for C41

[nickandre]

I'm debating mixing a bleach at home to use in my C41 process. Can someone give me a comparison/rundown on the differences?

All I need to do is remove the silver, either into halide or some other salt. I don't want to pay an arm and a leg either. What's the difference between say dichromate bleach and ferricyanide bleach? Which is better for my purpose?

I've looked at Ferric EDTA but it's expensive.

 

[nworth]

PE is the expert on Kodak bleaches, and he may yet post the definitive word. I have heard that an alternative ferricyanide bleach is approved for use with C-41, but I do not have its formula. Here is the formula for SR-34, one of the alternative bleaches used for the ECN-2 motion picture negative process. There is no guarantee that it would be suitable for C-41, but the two processes are generally similar. For home use, you can probably eliminate the mold inhibitor and chelating agent.

Kodak SR-34 bleach
Alternate bleach for Process ECN-2 for motion picture negative films (Potassium “UL House” bleach)
Water (21 – 38C) 700 ml
Proxel GXL 0.07 ml (mold inhibitor)
Kodak Chelating Agent No. 1 30.6 g
Potassium hydroxide (45%) 42.7 ml
Potassium bromide (anh) 51.5 g
Acetic acid (Glacial) 7.65 ml
Ferric nitrate (nonahydrate) 35.7 g
Water to make 1 l
pH at 25C = 5.30; density = 1.070; total iron (ferric only) 5.1 g/l
Bleach motion picture film 3 minutes at 27C

 

[Photo Engineer]

That bleach is just fine but watch out for retained iron (ferric hydroxide), if you go into the bleach from the developer. The alkali carryover can cause a problem. I would suggest a mild 2% Acetic Acid stop and a short wash.

Almost any rehalogenizing ferricyanide bleach will work but you must use a sulfite containing stop bath and a wash before a ferricyanide bleach. Otherwise, the oxidation of color developer carried into the bleach can cause a very very high stain.

PE

 

[ahock]

so when we use this formula for C41, the time also 3 minutes at 27C? If I use this under 38C, what time should I use? Thanks!!

 

[Photo Engineer]

Although there are a lot of bleach formulas for color films that can be compounded, it is often possible that the bleach in question can leave a stain or affect long term image stability. Some also fail to bleach all of the silver and even a tiny amount can degrade color and change grain.

Copper based bleaches and Iron based bleaches are prone to leaving behind green and red stains in particular unless a complexing agent is used to remove the hydroxides that may form, or unless the process is changed so that the metal is removed before damage can be done.

In particular, strong oxidants can affect stabilzing chemicals in coatings placed there to prevent dye oxidation during storage. If these compounds are oxidized by a strong bleach, then the dyes will fade more quickly. OTOH, the dyes require a specific pH for each type of film. They are optimum for acid, netural or basic conditions.

It is best to use the bleach suggested for a given film, or one as close to that as possible.

So, while I can give a bleach formula, there is only a narrow range of possible right formulas that fall into an acceptable range.

Ferricynaide bleaches, such as I mentioned are among the strong bleaches which might affect the image stability of some films.

PE

 

[nickandre]

I gave up on this and bought the last bottle of Bleach III I could get my hands on.

 

[PHOTOTONE]

I gave up on this and bought the last bottle of Bleach III I could get my hands on.

Rest assured, you can still get C-41 bleach, by mail order, even if your local supplier is unwilling to stock it.