You can turn the lights on, from the moment the print hits the bleach. It is acidic enough to prevent any more developing. You may then see when enough bleaching has been done. After enough runs, you can tell when the development has been correct too.
There is no chemical reason not to use sodium bisulfate (sodium hydrogen sulfate). It is a safer alternative to concentrated sulfuric acid. Either bisulfate or dilute sulfuric acid are capable of providing a low pH for the bleach.
Originally Posted by spoolman
Sulfuric acid can be purchased in dilute solution 10% to 51% as battery electrolyte. Any store that sells batteries should have it. The percentage of sulfuric acid should be given on the label.
The secret to BW reversal processing is to judiciously follow a method that is known to produce good results. Another tip is that everything thing works backward. If your slides are too light then you must decrease camera exposure.
I actually prefer the tones of the first picture = it's gives you something different from the norm that you seem to be aiming for ie white hightlights. Each to their own I suppose. :)
I saw this thread pop up with a new post today and started reading it and I have a question. I've been thinking about doing paper reversal so I figured I'd ask. The above quote recommends mixing Potassium Permangnate and Concentrated Sulfuric Acid which I was under the impression is something that would be a bad idea (and I haven't seen it suggested elsewhere).
Originally Posted by spoolman
Taken from Wikipedia (which I know isn't the best source of information):
"As an oxidizer that generates the dark brown product MnO2, potassium permanganate rapidly stains virtually any organic material such as skin, paper, and clothing. Solid KMnO4 is a strong oxidizer, thus should be kept separated from oxidizable substances. Reaction with concentrated sulfuric acid produces the highly explosive manganese(VII) oxide (Mn2O7). When solid KMnO4 mixed with pure glycerol or other simple alcohols will result in a violent combustion reaction."
is this a moot point since you're diluting each part with a liter of water or is it still something what shouldn't be done?
Wiki Link http://en.wikipedia.org/wiki/Potassi...y_and_handling
Well it is a bleach and that's what bleaches do.......mask, glasses and gloves are in order. Mixing is probable where most care should be taken. The acid get's reduced to %2 / vol and I use 12g dichromate / l. I'm not sure of the permanganate would be any different.
As far as staining is concerned, some films do and some do not. I guess it would depend on what the base is made of. I'm guessing RC would fair better than rag.....but you may enjoy the look. In the past I have selenium toned (archival) the film which didn't hurt the look of the film (my opinion).
Thanks for the response. I wasn't referring to the staining but the part of the quote that says: "Reaction with concentrated sulfuric acid produces the highly explosive manganese oxide ". I was just wondering if mixing even diluted Sulfuric Acid w/ the Permanganate would be a potential problem as this is the only time I've seen the mixture suggested regarding paper reversal.
Originally Posted by mrred
Your caution is to be commended because many of these chemicals are potentially dangerous.
However - combining dilute Sulfuric acid with Potassium permanganate solution to make silver bleach has been known for a very long time indeed.
I've done a decent amount of reversal testing using permanganate bleach, and I haven't managed to blow anything up yet, and I've never seen any reference to there being a problem with it forming explosive compounds - even here at APUG where there are plenty of proper chemists who would have advised special caution if there were any needed.
Permanganate bleaches are preferred by some as permanganate is much less toxic than Potassium dichromate, which is pretty vicious stuff.
Nevertheless like all photographic chemistry, you need to understand what precautions you ought to take.
FWIW, I understand that for paper reversal, a dichromate bleach is preferred as it is much less likely to stain. It has the other advantage of being quite stable (permanganate bleaches need to be mixed immediately before use, have only a very short working life once mixed, and are discarded after use, while dichromate bleaches can be reused)
Normally you would dilute the acid first. So I keep a 2 litre bottle of %2 and work with that. My guess you would need much much stronger acid to start a reaction of any consequence. The sulphuric acid I bought was %20 to start with. It's strong enough to need to be treated with respect but about half the strength that would be in your car battery. But there are better sources of that information here and I predominately use potassium dichromate. I do not know of any apug users that had their darkroom explode.
Perhaps PE can ring in on this.
This is new territory for me and even though I've read on it here and on other sites I figured it wise to ask.
Thank you both very much for the clarification.
You should definitely report back, successful or otherwise. I'm sure there would be a bit of interest on this.