Leafing through a book from 1904, I came across the following interesting hint:
"The addition of Sodium bisulfite to the fixer (plain hypo) is highly recommended. Not only will it increase the life of the fix, but it will also remove the unsightly brownish stain that sometimes occurs when using certain developers (notably pyrogallol)".
Translation and rewording from German is entirely mine.
Now my question is: Is this the reason nearly all commercial fixers are acidic? To REMOVE the Pyro stain??? Or does someone know differently?
I fear this could be another of those weird traditions from the days of glass plates - like the standard sizes for printing papers...
I am no chemist, but I think photographers eventually figured out that fix didn't break down as fast when it was made acidic. The problem was that it didn't fix as quickly when adidified, which was resolved by increasing the concentration of thiosulfate. Highly concentrated sodium thiosulfate acidified with sodium bisulfite, potassium metabisulfite, or sodium sulfite and acetic acid produces a long-lasting fixer with high capacity and reasonable fixing times. I suspect that the acid plays a primary role in reducing stain from pyro (just as it does when you use an acid stop), but I don't think that is the main reason for acidifying fix.
Actually not all fixers are acid. The so-called "neutral" fixers are not only useful for keeping pyro stain, they also provide better climate in the darkroom. They are nearly odorless.
The main reason why fixer usually is acid is to block remaining developer. Even if you use an acid stop, some developer might remain in the emulsion and might become active again in a basic solution. So fix should be at least neutral.
</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (tschmid @ May 2 2003, 04:28 AM)</td></tr><tr><td id='QUOTE'> The main reason why fixer usually is acid is to block remaining developer. Even if you use an acid stop, some developer might remain in the emulsion and might become active again in a basic solution. So fix should be at least neutral.
Acid fix actually breaks down faster than alkaline; it's the sulfite that preserves, not the acidity. </td></tr></table><span class='postcolor'>
This was not the reason given by E. Vogel in the 1904 book. Besides, the fixing process will effectively stop the development by removing the active silver halides: Monobath developers/fixers are very concentrated and extremely alkaline for this very reason. Unless the fixer is well past its usable life and the developer extremely concentrated, there will be no detectible development taking place in even the most alkaline fixers.
</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (OleTj @ May 2 2003, 02:47 PM)</td></tr><tr><td id='QUOTE'>Besides, the fixing process will effectively stop the development by removing the active silver halides</td></tr></table><span class='postcolor'>
Yes, of course. But it will take a while to process. Depending on the developer activity, another 30 seconds might not be negligible and may yield irreproducible results as the fixer wears.
Slightly off topic, perhaps...
Herr Vogel also recommends an acidic developer, based on iron (II) sulfate. "Plates developed in this solution have a beautiful blue colour". No mention of continued activity in acid fixer http://apug.org/forum/html/emoticons/wink.gif
I'm tempted to try this stuff on RC paper - might be interesting?
1) Hardeners needed an acid enviroment to work.
2) to protect against sloppy darkroom users.
I wonder if the second one was more an issue with fiber paper then film?
</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Robert @ May 2 2003, 08:51 AM)</td></tr><tr><td id='QUOTE'>1) Hardeners needed an acid enviroment to work.
I have abandoned acid in my fiber process totally - after develop (Neutol 1+11) I stop with 3 minutes/4 changes water. Then two baths of plain-fixer (mr. Adams style no acid) - then a holding-tray with water a few minutes before Selenium 1:20. The whole cycle is performed in one single tray - with no acid in neither step.
Am I missing something regarding hardeners here?
The research that I have been exposed to indicates that the reason for acid (either in the stop bath or in the fixer) is for the purpose of halting developer action. The control of the length of time in developing is important to me but I do realize that others compensate in other ways. The addition of Sodium Sulfite to the Sodium Thiosulfate in the fixing bath is that the Thiosulfate in reaction with the silver halides produces free sulphur as one of the by-products. The sodium sufite combines with the free sulfphur to produce sodium thiosulfate. As I understand it this is a secondary part of the process and effectively lengthens fixer life. I don't have any experience with the alkaline fixers, I do understand that some pyro users use an alkaline fixer to limit stain reduction. I have, however, not found stain reduction to be problematic when using ABC Pyro in conjunction with Acetic acid stop and hypo.