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  1. #11
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    Dichromate is not all that dangerous. I agree with Ian and Sandy. It does have problems, but it will remove silver and form the Silver Sulfate (soluable) salt and that is why the bleach is a mix of Dichromate and Sulfuric Acid.

    The problem is that it cannot be used in the C-41 process cycle unless you do the folowing process:

    Color develop as usual
    Stop + Sodium Sulfite
    Wash
    Bleach with Dichromate or Permanganate or Ferricyanide bleach - your choice.
    Clear bath of Sodium Sulfite
    Wash
    Fix
    Wash
    Stabilize.

    If you do not use the stop and clear as noted above you are going to have problems.

    Also, there is no guarantee that the C-41 dyes will survive the extreme acid of the Dichromate or Permanganate bleach baths. That is your problem.

    The same statements can be said about E6 use of these bleaches.

    PE

  2. #12

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    I don’t wanna add fuel to the flames, but still tend to disagree; it’s described to be quite poisonous, carcinogenetic, mutagen and teratogenic. It was "upgraded" in the mid 90's as far as I know. But OK, these nasty risks can be widely reduced by safe and accurate handling. Wearing nitrile rubber gloves, avoiding any skin contact and never ever inhale dust are the way to handle it. But it is stays potentially dangerous.

    LC50 for a rat is 0.094mg/L/4h inhaled…

    Lowest Published Lethal Dose:
    LDL [Man] - Route: Oral; Dose: 143 mg/kg
    LDL [Child] - Route: Oral; Dose 26 mg/kg

    Other sources claim that 0.5g till 1g swallowed kill a man (most likely a child), the truth will be somewhere between. Store it well and safe !
    Absolutely nothing to use without need, a color bleach does not have to be that poisons. The old stlyle Potassium ferricynide looks nearly healthy, compared: LDL [Rat] - route: Oral; Dose: 1600 mg/kg, (LD50) [Mouse]: Oral: 2970 mg/kg (Potassium ferricyanide)
    Being aware that there are more noxious substances and no one intentionally “messes around” with chemicals, common darkroom chemicals can be described as “fountain of youth” if compared. Well, maybe accidently hydrogen cyanide releasing compounds excluded…

    Further concern is putting this into the drain after usage; Chromates tend to slip through sewage plants or can harm the microbes for biological treatment. ChromVI is very poisonous for flora and fauna in rivers and seas and does not vanish due sedimentation, it too soluble…maybe a biologist can describe this better…

    These are my information and this stuff is one of the few (hobby) lab chemicals I give to hazardous waste collection after (very rare) usage.

    Regards,
    Stefan

  3. #13
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    Thanks for the tips Photo Engineer,

    So, I can always make the working solution weaker for colour?

    Hmm I'll do more research, vanbar has all of these different chemicals for sale, so I do have a choice of what I can make

  4. #14
    mts
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    Your Pot. dichromate/sulfuric acid "bleach" is called tray cleaner in the old Kodak B&W formulas booklet. It works to clean out badly stained trays and bottles but isn't good for the environment. A similar chromic acid compound was used as boiler cleaner to clean steam lines for many years until it too was banned for the above mentioned environmental and health reasons. It's certainly not acceptable as bleach for film. The ferricyanide formula can be used as PE notes, but it is by no means ideal for modern films. It was the original C-22 bleach for Kodacolor-I, II when those emulsions were introduced well before C-41 came to life.
    By denying the facts, any paradox can be sustained--Galileo

  5. #15

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    Quote Originally Posted by Athiril View Post
    carcinogen? so if i wear a dust mask, and rubber gloves it's still a bad idea to handle?

    I guess copper sulphate bleach would be much better than.

    What kind of disposal? patch of lawn in the corner?
    Not all dust masks are approved to be effective with chromates dust. Wear only approved dust mask or integral respirator (consult your local authority since dust mask types vary with countries).
    You should wear NIRTILE gloves (not simple rubber ones) and safety goggles, apron ecc...

    Mix the required amount in open space to minimize airborne dust.

    Permanganate doesn't damage emulsion if use half-strenght of what's recommended.

    However the dichromate bleach won't work for your intentions...

    :-)

  6. #16
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    Quote Originally Posted by Athiril View Post
    Thanks for the tips Photo Engineer,

    So, I can always make the working solution weaker for colour?

    Hmm I'll do more research, vanbar has all of these different chemicals for sale, so I do have a choice of what I can make
    I didn't say that.

    PE

  7. #17

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    I used Kodak's "system cleaner" for my BW reversal bleach...easier than mixing it from scratch

    re:toxicity ....doesn't the sodium sulfite bath turn the hexavalent chromium into a less nasty valence of chromium?

    the first time I used this bleach it was about midnight and I realized I had the dichromate, but no acid...I went out to my car with an eyedropper and a huge grin...took 12ml of acid out of my car battery...worked perfect

  8. #18
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    Battery acid is about 35% sulfuric acid or thereabouts. It will work.

    Chromium is chromium and can be toxic in several valence states so as I said above... It is not as bad as all that, but it is not benign by any means and in any state. Be careful.

    The sulfite is more to reduce the dichromate so that it does not destroy the hypo in the fixer and it does not stain the film with chromium salt mixes.

    PE

  9. #19
    RPC
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    Is it necessary to use a clearing sulfite bath when using ferricyanide? I have used a ferricyanide bleach along with the stop + sodium sulfite, but not the clearing sulfite bath after the bleach step, and have not noticed any problems.

    RPC

  10. #20
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    Ferricyanide will oxidize hypo very rapidly and form sulfur, sulfur dioxide and hydrogen sulfide. The sulfur can cause a haze in your film and the overall oxidation can reduce the life and capacity of the fixer.

    The choice of what to do is yours. If it works, what can I say but let you know what may happen.

    PE

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