Why acid fix?

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (Darkroom ChromaCrafts @ May 6 2003, 06:09 PM)</td></tr><tr><td id='QUOTE'> </span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (OleTj @ May 2 2003, 02:49 AM)</td></tr><tr><td id='QUOTE'> Leafing through a book from 1904, I came across the following interesting hint:

&quot;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)&quot;.

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... </td></tr></table><span class='postcolor'>
Well, I wonder if that is why I have five bottles of the stuff around the shop. I got only about 15 days of actual training and I keep coming across chemicals I have no idea what to do with. I just found out how to use potassium ferrocyanide about a month ago. I got about a pound and a half of it.

What proportions did the book suggest. . . </td></tr></table><span class='postcolor'>
If you're using commerically prepared fixer I doubt you need to worry. I think you're asking about the sodium bisulfite? Most commerical chemicals aren't likely to be improved by adding things.

For the unknown chemicals you could try Jack's chemical website:

http://www.jackspcs.com/chemdesc.htm

Also you might want to look at:

The Darkroom Cookbook by Anchell and Troop.

But unless you're mixing your own chemicals up I don't know if you really need to.

</span><table border='0' align='center' width='95%' cellpadding='3' cellspacing='1'><tr><td>QUOTE (dnmilikan @ May 6 2003, 03:04 PM)</td></tr><tr><td id='QUOTE'> For that matter when one reviews the PH of Sodium Thiosulfate, it is shown to have a PH of 11. That is certainly alkaline.

When one reviews the PH of Sodium Sulfite it is shown to have a PH of 9.5. That is certainly alkaline as well.
</td></tr></table><span class='postcolor'>
According to my MSDS, Sodium Thiosulfate solution has a pH of 6.0 to 8.5 - not alkaline at all!

Sodium Metabisulfite - 4.0 to 5.0 - acid

Sodium Sulfite - 8.8 to 10.0 - somewhat alkaline.

"Very often, photographers who are accustomed to an acid fixer odor need to get used to the Alkaline pH fixer smell. The Alkaline pH fixer is more gentle than the acid."

This was in the email newsletter sent out by Fine Art Photo Supply.

TF-4 has a mild ammonia smell--milder than, say, household ammonia. It's not odorless, but I'm prone to respiratory problems, and I find it less uncomfortable to work with.

A good non-acidic fixer is Agfa FX-Universal, primarily sold for colour processing, but ideal for B+W film and paper unless you need hardener. Diluted 1+5 it has pH=7.5 approx, so it's effectively neutral. It smells very slightly of ammonia. Much nicer in the darkroom. Also, it's relatively cheap.

dnmilikan said:

The net result of this chemical reaction is lengthening the effective life of the fixer solution. This chemical reaction will continue so long as there is either the Sodium Sulfite or the Sodium Bisulfite present in solution for the free sulphur to recombine with.

Click to expand...

So the Sulfite has no real benefit for the fixing process itself? I am about to exclude the Sulfite and use a fixer consiting of Thiosulfite only as a one-shot (one-session) fixer for paper.

Bill Troop, co-autor of the development cookbook (or similar tiltle) and TF-2, TF-4 fixers posted a long thread in rec.darkroom news group of why alkali fixers.
In short, he says (but many did not agree) it washes better.
Usually they are not hardening fixers (but it could be done).

Since they do not smell, I decided to use it for paper.
For films, I use an acid hardening fast fixer.

Jorge O

I now use mostly TF2 for paper. For film, since I tend to use staining developers - and wish to preserve the stain - I mix a little Ammonium Chloride in plain hypo. So it can't be stored overnight? So what? I mix only as much as I need for one round of processing, and buy my hypo in 25kg sacks. I see no reason to skimp on the fixer, nor for worrying about exhaustion...

Ole

This information re ammonium chloride fixers not suitable to storage is new for me.
It doesn't keeps or what?

Jorge O

jansenh said:

So the Sulfite has no real benefit for the fixing process itself? I am about to exclude the Sulfite and use a fixer consiting of Thiosulfite only as a one-shot (one-session) fixer for paper.

Click to expand...

Some place in one of the Adams books [The print??] he mentions plain hypo for the second bath in a two bath setup. All the sulfite does is let you keep the stuff.

Jorge Oliveira said:

Ole

This information re ammonium chloride fixers not suitable to storage is new for me.
It doesn't keeps or what?

Jorge O

Click to expand...

I don't think he meant that. The lack of a perservite in the fixer is the problem.

Thanks, Robert

Jorge O

Robert said:

I don't think he meant that. The lack of a perservite in the fixer is the problem.

Click to expand...

I must have made myself even less clear than usual

You're right, Robert.

Since Sulfite, as well as acidity, reduces the stain from pyro/pyrocat developers, it seems like a good idea to me to reduce their (fixer additives, not staining developers) use.

This whole thread started with my discovering a recommendation to use acidic fix (sodium bisulfite) to remove the ugly stain on negatives developed in some developers, notably pyrogallol.

It looks as if we now mostly agree that this might well be the case?
So: Since I want to preserve the stain, I will drop both acidity and sulfite.

Since one of the primary reasons for using a stop bath is to preserve the acidity of the fixer, that goes out the window too. Unless I need to stop development immediately, of course. Which I mosty don't...

..