C41 and E6 bleach at home recipe?

[1kgcoffee]

This question is geared to more chemically inclined members of the forum

Just curious about what the difference is between C41 and E6 bleach? My understanding is that bleach is to completion but will gradually lighten the image if extended.

If I don't have a kit and wish to home brew c41 and E6, how would I go about bleaching the films in separate bleach and fix steps? Could ferricyanide bleach be used or is there a better choice? Is there a different temperature needed? I have also read previously that the film should be washed and cleared before fixing. What does this entail? A hypocrite clearing agent (s sulfite?) Or plain old water for a few minutes? Could there be any negative side effects such as off colours or long term stability by home bleaching?

Thanks in advance,
1kgcoffee

 

[Anon Ymous]

C41/E6 can be effectively bleached with a ferricyanide-bromide bleach, but their longevity might suffer. PE has stated this several times. Both films can be bleached with a Ferric Ammonium EDTA based bleach, although nowadays C41 bleaches are based on PDTA, or NTA. You'd be lucky if you can find a local source of Ferric Ammonium EDTA, usually provided in solution. This is the single most expensive and hard to source bleach ingredient. If you can't find a source, then you'd have to make your own, but this still assumes that you can source some other chemicals easily and/or cheaply.

First of all, you'll need EDTA-2Na, or 4Na. You can get the free acid from it if you follow the method described here by Rudeofus. Note that you'll also need sulfuric acid, or sodium bisulfate. Assuming you have some EDTA free acid, then you'll need to mix it with a source of Ammonium and Ferric ions. Ammonium Bicarbonate, or Ammonia are the obvious choices. For the Ferric part you'd have to use something like Ferric Chloride, or Ferric Nitrate. You can also precipitate Ferric Hydroxide from Ferric Chloride and use this instead, but this is messy and requires some borosilicate glass beakers and boil the reagents. It's quite a messy process to be honest.

If you get your Ferric Ammonium EDTA solution, then you need to add Ammonium Bromide and correct the pH. This basically gives you a bleach that can be used for both, although bleaching times may suffer if you don't use a bleach accelerator. Anyway, a C41 bleach formula can be found here and an E6 one here.

The film must be washed between the bleach and fixer baths. Water rinses with agitation are fine.

 

[Rudeofus]

In my experience a bleach mixed from Ammonium Ferric EDTA and Ammonium Bromide alone will not work, it needs a bleach accelerator. My E6 slides processed with a bleach sans accelerator always had brown stain. I recommend you add 0.1 g/l Mercaptotriazol to your bleach, it can be obtained from Suvatlar and probably Formulary. Do not add more than these 0.1 g/l or the bleach will become slower again. An even better way of adding measured amounts of bleach accelerator is by using a prebleach. If you look at the Fuji recipe linked to by Anon Ymous, you can replace the 0.4 g/l Thioglycerol with a similar amount of Mercaptotriazol and leave out the Formalin Bisulfite adduct, the remaining components are moderately easy to obtain.

If you look at my article about "converting BLIX to bleach", the reason why you don't have to add a bleach accelerator there is because it's provided in the bleach component of BLIX kits. It's not listed in MSDS, but there is a substantial difference between bleaches mixed with Tetenal's BX1 and those mixed from straight Ammonium Ferric EDTA.