The chemistry is complex but essentially what is happening is an ion exchange. The adsorbed thiosulfate ions remaining from the fixing process are displaced by sulfite ions. This makes the washing process (essentially a diffusion process) more efficient as adsorbed thiosulfates are relatively slow and difficult to diffuse out of the emulsion/paper.
So sulfite ions are easier to wash out?
Very informative.
Thanks!The problem with reusing a washing aid like HCA is that the alkaline medium combined with bits of emulsion provide a great breeding ground for various kinds of bacteria. This is what causes the slime that forms in a reused bath that many people observe. There are ways to prevent this like the addition of Liserine but the easiest (and best) is just to discard the bath after use.
what michael said ...
think of it this way ...
you fixed the paper ( or film )
and after you rinsed the print ( or negative ) off
you still have fixer kind of loitering and no matter how much they are told to take off they don't ...
the perma wash, hypo clear, fixer remover ... whatever you want to use
is absorbed into the print / negative and displaces/grabs the fixer and drops it out of the print/negative
so in the end you aren't washing out as much fixer, but the fixer remover which doesn't mind
getting washed off/ getting kicked your print/negative for loitering ... so your wash times are shortened ...
from what i have read ...
they learned about this stuff during the 2nd world war when the us navy ( and maybe others? ) started to wash film and paper in sea water
( which contains a lot of sulfites ) and shortened wash times so save on fresh water. so after ww2 photochemistry companies
figured out what it was in the sea water that did this and sold it as a product ...
Does a bath containing significant amounts of Sulfite really allow germ growth, or is germ growth an indication that all Sulfite has been converted to Sulfate and the bath should be replaced ASAP?
I think they should still be fine, Wade. The hardness would be due, as with all dry chemicals, to the absorption of moisture from the air. They should still be perfectly viable. I don't think atmospheric conditions deteriorate sulfite.
Quick question - is it necessary to agitate when in the Hypo Clear? Or is it best to let it sit and do what it does?
I always agitate lightly to make sure fresh solution reachea ll parts of theemulsion.
I have a couple of questions about using HCA. Normally, I wash my prints out of the 2nd fix for about 10 minutes than soak my prints in HCA for about 15 minutes than wash 30-45 minutes. I'm going to have to change my washing work flow due the the California drought. Does soaking overnight reduce wash time? Also, I've read an article from David Vestal that it's safe to wash prints back to back in an archival print washer. I'm actually thinking about washing my prints outside so I can water my landscaping.
The question is: who came up with the idea to research this? Intuitively one would expect that the purest form of water would be the best washing agent, but evidence existed that impure water is much, much better. Even if some parts of the world knew that impure water is better, this bit of information may not have been present on navy ships and could have simply been discovered independently. Note that relevant research about this topic stretched well into the seventies.that's a nice story and most likely an urban mythbut, is a possible explanation.I have more trust in photographic research.
Sodium sulfite is a known solvent (see developers)and it's application for fixer removal is not a far-fetched idea.Agfa and Ilford tried othercompoundsbut,sodium sulfiteturned out to be most effective.So, probably not a lucky coincident at war but a scientific approachBut I agree, it makes the better story,
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