Sodium Thiosulfate "Plain Fixer" question

[ZoneIII]

150 grams of anhydrous sodium thiosulfate would give a 15% w/v solution when dissolved into 1 L of water.

I've never heard of two-bath fixing ever ruining film. In fact, I've been using it for about 20 years now and never had a sheet (or roll) ruined by it - from colloidial sulfer or otherwise.

I recommend two-bath film fixing as a great way to ensure complete fixing.

Funny, I have been developing film for over forty years and I don't remember hearing of anyone fixing film twice. It is completely unnecessary. Now, with fiber base paper, two fixes is the traditional method. But film? No.

[ZoneIII]

Better Sense:

2 bath fixation: I first came across this shortly after WWII when Europe was in a mess. The purpose of it was to first fix in old nearlyexhausted thiosulfate and then fix in fresh thiosulfate fixer, this to extend the life of fixers at a time when supplies were frequently low and always high in price. It seemed like such a good idea until some time later when sulfiding of films and prints destroyed the silver based products.

In near exhaustion, fixation takes place slowly but under those conditions, coloidal sulfur (at that time invisible) absorbs and subsequent fixes and washes will not fully remove it. Hence, oxygen, silver, and sulfur do their brown fugitive magic.

One fresh fixer is always preferable to any other choice.

Lynn

Well said!

[Harold_4074]

Pure sodium thiosulfate in solution is unstable in the presence of even a weak acid. In my experience, a liter of solution in an open two liter beaker will turn cloudy in a matter of days, due to carbon dioxide having dissolved in the water and formed carbonic acid. (This was a mystery when I first observed it, but a 1937-vintage chemistry text describes it explicitly.) The cloudiness is precipitated sulfur, which could definitely be trapped by paper fibers, probably oxidize to form sulfurous acid, and possibly cause eventual fading of a silver image.

Elemental sulfur is insoluble in water, so washing will remove it only mechanically. However, sulfur reacts with sulfite to form thiosulfate, so hypo clearing agent will (at least theoretically) dissolve it. Ironically, the usual advice is that "HCA is only needed if an acid fixer is used", implying that plain hypo would make it superfluous.

Both alkali and sulfite from developer carryover will tend to suppress the decomposition, so it would seem that the greatest risk would come from fixing in a tray (large surface-to-volume ratio) of pure (no added sulfite or bisulfite) hypo solution following a running-water rinse in lieu of stop bath, particularly in the absence of an HCA treatment before washing.