[pure-silver] Re: Fixer Stain Removal
----- Original Message ----- From: "Jean-David Beyer" <jeandavid8@xxxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Monday, November 09, 2009 2:54 AM
Subject: [pure-silver] Re: Fixer Stain Removal



Richard Knoppow wrote:
----- Original Message ----- From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Sunday, November 08, 2009 4:21 PM
Subject: [pure-silver] Fixer Stain Removal
What is the latest wisdom on removing fixer stains? I've tried a 50% citric acid solution with limited success but like to get something 
more 'agressive'.





Regards



Ralph W. Lambrecht
Describe the stains. If they are silver stains you may have success by using fresh acid rapid fixer with added citric acid, about 15 grams per liter. This is a mild solvent for metallic silver. For sulfide stains I think one has to resort to stronger bleaches like Kodak TC-3. 

Solution A
Water                            1.0 liter
Potassium permanganate           2.0 grams
Sulfuric acid (concentrated)     4.0 ml

Store in a stoppered bottle away from light.

Solution B
Water                            1.0 liter
Sodium bisulfite                30.0 grams
Sodium sulfite, desiccated      30.0 grams
It appears that the sodium metabisulfite of commerce is the same substance as called sodium bisulfite in Kodak formulas.
To use treat stains with a small amount of Solution A, then rince well and treat with solution B. Then wash.
I will look at some other sources for clothes specific stain removers. 


If I remember my chemistry correctly (about 50 years ago),
you cannot purchase sodium bisulfite because it does not exist in solid form. Sodium metabisulfite is readily available in solid form and absorbs water to become sodium sulfite when mixed with water. Wikipedia does not hold this opinion and describes each. the bisulfite one is HaHSO3 and the metabisulfite is Na2S2O5. In other words, they are really the same compound, but the one is a dessicated form of the other and perhaps both exist in the dry state. Now what you have if you cannot keep them both dry enough is anybody's guess, probably a mixture of each.
We should from what substance the O.P. wishes to remove the stains. If it is something like a metal tray, or perhaps even a plastic tray, TC-3 would be fine, but if it is on clothing, that may be too strong and damage it. 

--
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TC-3 was recommended for removing silver stains from the hands so it can't be too strong but some cloth is pretty delicate. There was a long discussion in one of the lists or, perhaps, in the darkroom Usenet group about sodium bisulfite. That is why I mentioned the metabisulfite. The bisulfite specificed by Kodak is actually the metabisulfite. Kodak evidently used some old chemical terminology, but then these formulas are all quite old. This is also true of Ansco/Agfa formulae and probably all other photographic formulae of the time. 

--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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