From: Monnoyer Philippe (monnoyer@imec.be)
Date: 02/14/03-09:42:34 AM Z
Hi Jack,
you say:
"but, I wonder why the great stain using the permanganate bleach vs the dichromate."
Well, the reason is that potassium permanganate, when it bleaches, meaning when it oxydises, or when it is getting reduced, turns into manganese dioxyde, a dark brown non-soluble powder that stays in the fibers etc.
On the other hand, dichromate does not produce such a reduced dark molecule, and moreover, the reduced form of dichromate is still soluble and remains dissolved in water. That's why nothing stays in the paper.
I personnaly would tend to use non-toxic bleaches based on other formulations.
Cheers,
Philippe
|-----Original Message-----
|From: Jack Fulton [mailto:jefulton1@attbi.com]
|Sent: Friday, February 14, 2003 16:22
|To: alt-photo-process-l@skyway.usask.ca
|Subject: Re: Pt IV to Pt II
|
|
|Richard . . . I mixed both bleaches the other day for knowing that the
|permanganate is used in a 'cleaning' solution for photo stains I'd not
|thought of it for my reversal work. But, in doing so and using on fiber
|paper there was a strong stain. I further found that there are
|two formulae
|for the clearing baths employing the permanganate and
|dichromate bleaches.
|My literature says to use Potassium or Sodium Metabisulfite for the
|permanganate bleach and just Sodium Sulfite for the
|dichromate. Ilford's
|formulae says only to use Sulfite for the permanganate. But,
|there I was
|with this horrendous stain. My chemicals books suggest the Potassium
|Metabisulfite replaces Sodium Bisulfite weight for weight and
|that it does
|the same things as Sodium Sulfite . . . but, I wonder why the
|great stain
|using the permanganate bleach vs the dichromate.
|Hope I've made this clear so early in the morning.
|Jack
|
|
|
|>>> Someone, recently, posted a formula for a bleach used in
|> reversal
|>>> processing.
|>>> As I remember, it was Potassium Permanganate and Sodium
|> Bisulfate. I
|>>> actually cannot find any reference to this bleach. I
|> also think it was
|>>> referred to as a modified Kodak R9 bleach. My records
|> indicate the R9
|>>> employs Potassium di(or bi) chromate and Sulfuric Acid.
|>>>
|>>> Any ideas folks?
|>>> Thanks
|>>> Jack
|>>>
|> I can't find either R-9 or modified R-9 but reversal
|> bleaches are all about the same. Here are two.
|> Bleach No.1
|> Potassium bichromate 5.0 grams
|> Sulfuric Acid 5.0 ml
|> Waer to make 1.0 liter
|> As always, add the acid slowly to the water. Sulfuric
|> evolves a lot of heat when it goes into solution.
|>
|> Bleach No.2
|> Potassium Permanganate 2.0 grams
|> Sulfuric Acid 5.0 ml
|> Water to make 1.0 liter
|>
|> The permanganate bleach softens the gelatin more than the
|> bichromate bleach.
|> Alt processes people should be well aware of the hazards
|> of bichromate.
|> After bleaching in either bleach the film should be
|> cleared in:
|>
|> Clearing bath
|> Sodium bisulfite 50.0 grams
|> Water to make 1.0 liter
|>
|> Sodium Sulfite or Sodium metabisulfite may be used weight
|> for weight for the bisulfite.
|> ---
|> Richard Knoppow
|> Los Angeles, CA, USA
|> dickburk@ix.netcom.com
|>
|>
|
|
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