B&W Reversal Bleaching Question

davido · Jan 15, 2007

hello

I attempted my first B&W reversal yesterday. I used the instructions on the Ilford website which call for potassium permanganate /sulphuric acid bleach. The instructions say that a 5 minute bleach is generally enough but one should continue " as long as it takes to remove the silver image". Well, after 20 minutes there was still an image on the film. The film was also not a creamy-yellow to which the instructions also refer. I pulled the film anyway and continued with the rest of the process. After exposing the film, I was thrilled to see a possitive image (if somewhat weak); however, after developing, fixing and washing, the film was completely blank.
Obviously, I had bleached the film way too long. I was waiting for the image to completely dissapear. Is this not the case?
I also realized later that I was looking at the film base and not the emulsion during the bleaching stage. The film base looked a purple blue which was mostly the pot. permanganate.
My question is: does the image remain through the bleaching process and if so how does one know when the bleaching is complete?

thanks
david drake

Jordan · Jan 15, 2007

The bleach step removes the silver negative image. However, the stain left by the bleach can make it tricky to tell when the bleaching process has completed unless you do repeated bleach-wash-clear cycles.

What I do is to take a piece of exposed and developed leader (just scrap film) and drop it in some bleach solution at the same time as I begin bleaching my film. I can then check its progress (by removing it, washing it with water and dunking it sodium metabisulfite solution to clear the stain) without disturbing my film.

One caveat about permanganate bleaches is that they soften the emulsion considerably. That may be why you got no image after extended bleaching (the emulsion can literally float away). Your choices are to either go to a dichromate bleach (significantly more toxic, but re-usable, and much easier on the emulsion) or to be very careful about your film handing and avoiding temperature changes.

Jordan · Jan 15, 2007

I simul-posted with Alessandro. He's the go-to guy for how to use permanganate bleach without trashing your film.

davido · Jan 15, 2007

thanks Jordan & Alessandro for your replies. I've seen your names on many past threads to do with this issue, so I was pleased to see your replies here.
I'm still confused as to whether it is normal to see the negative image, through the base side of the film, after 15-20 minutes of bleaching (or is this a stain)?
I'm seriously considering using the potassium dichromate bleach for this process (since I already have some). Are you still using version with sodium bisulfate Jordan? I'm not crazy about using Sulphuric Acid.
thanks very much,
david

Dug · Jan 16, 2007

What color was the film after bleaching?

My recipe for bleach Part A is 4gm Pot Perm/per 1L of distilled H20 (like the others). I use 250 ml of the Pot Perm bleach, and 235 ml of distilled water which I have added 15ml of battery acid (35% sulfuric acid) for Part B. This creates the 500ml of bleach needed for a roll of film. I also give a quick rinse of distilled water to the film before the bleach step. Any chlorine before or in the bleach process creates disaster for me.

I use the formula described in the Photographer's Formulary Reversal Chemistry instructions but substitute the bleach formula above for their bleach concoction.

Let us know how it works out!
It took many tries before I got it to work to my satisfaction.

davido · Jan 16, 2007

Thanks very much for posting the .doc file Alessandro. Your detailed notes are fantastic. I will definately work with the Permanganate further. I am also glad that sodium bisulphate can be used with the permanganate instead of sulphuric acid.
I am still curious as to whether it is normal to see a negative image
on the film (through the film base) even after bleaching?
thanks
david
Dug, the colour of the film emulsion was creamy yellow after bleaching. thanks for your advice. I'll let y'all know how it goes.

dr5chrome · Jan 17, 2007

reversal bleach.

The results you will see with Di-chromate will far out weigh its hazard.
Frankly, the hype about this agent is way overblown. I will not dispute some folks opposition to it, that is their prerogative. With out Di-chromate's so many things in our lives would not be possible. Just treat this agent, and any other for that matter,, as you would any chemical, and protect yourself. You're not going to get cancer and die by having this agent in the room.

You can use several types of acid [don't have a list at hand] in reversal processing, however sulfuric is the most efficient, test, test, test.... You're bleach step should be no longer than 6 min. Adjust your mix strength for this time.

Though more expensive you could try CERIC-SULFATE. We have found fair results with this agent.

The problem with permanganate is it is very powerful. Its use is one-shot. As Jordan noted, Di-chromate has a very long life. Another perk to using Dichromate or Ceric-sulfate is reclaiming the silver. It is nearly impossible to extract the silver out of a permanganate bleach. Reversal B&W processing packs the silver in the bleach not the fixer. The Kodak kit [might be wrong here] I believe is designed to take the silver out as E6 does, in the fixer [someone here know this?]. I don't know if this kit is still available.

There are many reversal processing procedures. They are not all equal.
Best to find something that works best for you. If your shooting medium format, a good film to start with is KODAKS TXP. Not only is this one of the best B&W films made, it has a very tough emulsion better suited for permanganate bleaches. TMAX100 is good too for permanganate bleach but tends to have creamy look.

regards
dw

http://www.dr5.com

Photo Engineer · Jan 17, 2007

Among other things, permanganates will create explosive mixtures with some common darkroom chemicals. Just mixing potassium permanganate with XXXX will cause a violent explosion in your face!

I do not keep potassium permanganate in my darkroom.

PE

dr5chrome · Jan 17, 2007

..i am very please you are happy with your bleach.

i don't believe i have replied to you on any forum on this issue, but I have several emails from you about a year ago when you were having problems with your recipe, i was happy to help.

Funny thing is i never read Haists book until recently [about a year ago]. It is very coincidental the information in his book mimicked my own conclusions, however there are still some things he states i have proven wrong in my time in the dark. You are wrong BTW that he states permanganate yields better results... read his book again. Haist also mentions Hydrazine in his book, which happens to be in his reversal processing section. PE is the hydrazine expert here.

I wonder just what you really know about Di-chromate and what it is used for? The Leather in your closet was likely treated by it, so don't lick your leather. Anything that is plated goes through a di-chromate bath. Also; synthetic perfume, electroplating circutboards, drycell batteries, ceramics[color paint], fly paper, and don't take a whiff when someone lights a match or sets off fireworks. Just calm down about this, would ya...

ive taken enough grief on this forum regarding chemistry so ill call it quits for now.

I consider myself an expert regarding reversal B&W processing but that seems to not matter here. While what i say isn't worth sawdust on this round-table, I have processed 10's of thousands of B&W transparency rolls and sheets since 1991.

We all guessed your dislike for Di-chromate, we get it. It is very good you have devised good results with permanganate, BRAVO! HAPPY to see it!! ..so what do you do with the waste? Do you dump all that silver down the drain?

regards

dw

http://www.dr5.com

Photo Engineer · Jan 17, 2007

Alessandro;

Potassium Permanganate explodes on contact with many chemicals but Potassium Dichromate does not. Potassium Permanganate generates the poison gas chlorine on contact with Hydrochloric Acid. The list goes on and on and on.

Permanganates are far more reactive as oxidants as Dichromates and are no longer recommended by Kodak as a bleach due to this problem.

You may use what you wish. I don't care. I don't use any permanganates or keep them in my home. I have worked safely with both permanganates and dichromates for years, and also with many peroxide oxidants. My thesis was on the oxidation of hydrazine derivatives with peroxy compunds and other oxidants. I do know this field very well.

PE

Jordan · Jan 17, 2007

I think that both dichromate and permanganate have their plusses and minuses. Both are extraordinarily reactive, and I wouldn't want to eat or breathe either of them, but the chronic toxicity of dichromate is much higher. At the same time, bleaches based on dichromate remain stable for quite a while, while permanganate bleaches must be mixed fresh all the time -- which requires more handling.

I think all of us would agree that reversal processing involves materials that are "above-and-beyond" conventional B&W processing in terms of potential hazards... I discourage people who are unable to handle chemical reagents safely from doing home reversal processing, for this very reason.

Photo Engineer · Jan 17, 2007

Jordan;

I couldn't agree more.

PE

Photo Engineer · Jan 18, 2007

Alessandro;

Unfortunately, many states/countries panicked over the cancer news about dichromates and as such they (Kodak) had to make a choice. I used he Kodak permanganate bleach years ago as a teen when it was discontinued due to fire hazard and now it is coming back.

But, you miss our point I think. Our advice is pointed towards those who don't use chemistry. It is easier to cope with a bit of dust by using a mask and gloves than it is to cope with a sudden explosion and fire.

The first demo we had in HS chemistry was safety. The teacher told us that Chemistry was no walk in the park. He showed us that potassium permanganate looked like 'dried grape juice' and then proceeded to pour on a common household product that looks like water and it exploded right on the lab bench. He taught us care and safety in one instant that day. We each had to repeat his experiment.

I have worked with reducing and oxidizing agents such as hydrazine and peracetic acid and violent reactants such as pure liquid chlorine and solid sodium metal. These are extremes. But on that scale, dichromate and permanganate are oxidants and per signifies stronger. It is a worse oxidant but less toxic. I don't like having it around.

Use what you wish. I think anyone can handle either chemical with precautions as long as they know what to expect and use due caution for either type of situation.

PE

radiantdarkroom · May 24, 2007

Hey has anyone else used Kodak's Part B Rapid fixer as a substitute for sulfuric acid used in the Bleach, and Undiluted Kodak's Hypo Clear as the clearing agent
I get awesome results with these substitutes. I haven't been able to find a good substitute for the permanganate or Dichromate.

Lowell Huff · May 24, 2007

I agree with David. Chromate bleach does give a better result than does permanganate bleach. As far as "safety", they both have sulfuric acid based. So that issue then becomes relative.

B&W Reversal Bleaching Question

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