Don't we all?
The search for the mot juste is not a pedantic fad but a vital necessity. Words are our precision tools. Imprecision engenders ambiguity, and hours are wasted in removing verbal misunderstandings before the argument of substance can begin. (source unknown)
And likely any less than 100% Pure and a solution of
Originally Posted by Wolfgang Moersch
sodium sulfite is half strength in who knows how little
time. I've read that as little as one part per trillion
of copper will catalyze it's oxidation appreciatively.
Consider the dependence placed upon sodium sulfite
as the basis for world wide hypo clearing. I think it a
real concern that the only guides are Kodak's and
other's instructions on the package. Where are
some real world in use studies?
Personally I like the idea of a Stable substance such
as Agfa's recommended sodium carbonate. It MAY
even be the equal of sodium sulfite, and that at
the later's freshest. Dan
If you do a search in rec.photo.darkroom you will find much discussion of the merits of various wash aids, including some references to studies. My take on this after reading a lot of it is to use sulphite plus a bit of (meta)bisulphite since I am convinced that sulphite washes very well and that keeping the pH around neutral is better for the emulsion. If you make up a concentrated stock soultion (see the formula earlier in this thread) it probably keeps quite well, depending on your rate of use, and is cheap enough to discard each day.
You might find that common sodium chloride washes as well as the carbonate, and would have the advantage of not softening the emulsion. It is stable and cheap!
" ... it probably keeps quite well,"
Probably? You mean it's Maybe OK. A lot of
assurance that is.
"...common sodium chloride ...
It is stable and cheap!"
Sodium chloride. For it I've not seen a
single recommendation. Unlike some I give
Agfa some credit for sound reasoning when
Sodium carbonate is very low cost. More
Environmentaly friendly to boot. Dan
The reference to sodium chloride is based on the fact that it is the main ingredient in sea water. A number of posts that I have read (see above) use expressions like "Kodak found that sulphite washed as well as sea water". I don't know what else is in sea water. But it might be cheaper than even carbonate, but subject of course to transport costs or inconvenience.
Agfa's recommendation is worth considering. Also worth considering is the large amount written about sulphite and buffered sulphite. Personally, I have chosen to go with the majority for reasons that I find convincing. I do not use carbonate partly because I heat dry some of my prints, and the softening caused by carbonate would be a concern.
You have a valid point that sulphite solution does not keep well. I can not assure you that the concentrated stock solution will last as long as you might want it to. Like keeping developer, it depends on your rate of use. Alternatively, it could be kept in powder form (sulphite + bisulphite) and spooned into the water when needed.
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The logical next question is the hypo-clearing efficiency of sulfate.
That's what you end up with if the "sulfite doesn't keep". Is it better or worse than seawater? Than carbonate?
-- Ole Tjugen, Luddite Elitist
A lot that has been written on the subject dates from when hardening fixers were used. Maintaining the hardening during wash aid treatment was one of the reasons for buffering the wash aid. Carbonate appears to have been considered too alkaline for this.
Originally Posted by Ole
Now that hardening fixer is generally not used, that is not such an issue, although the pH of the wash aid is still considered worth keeping at around the level of the Kodak product. This is cut from a post by Richard Knoppow:
Sulfite seems to have a specific action
which carbonates and borates do not have. There were extensive
experiments made at Kodak Labs testing all sorts of salts. Carbonate
and metaborate will shift the pH of the emulsion enough to eliminate
the mordanting action of aluminum hardener but seem to have no other effect. The measured level of thiosulfate in an emulsion was reduced much more quickly after the sulfite bath than after bathing in any carbonate, sodium metaborate, or sulfate.
I have not read the original articles, but I trust Richard K enough to accept his summary. You can search rec.photo.darkroom for the article citations.
The "mordanting" referred to is the effect of the alum (potassium aluminium sulphate) in the most common hardening fixer of holding thiosulphate in the emulsion or paper, just as a mordant is used to prepare fabric to retain dye instead of letting it wash out.
John quoting Agfa:
A soda bath (1 % sodium carbonate solution) should be
included for fibre-base paper, between fixer and final wash
(time: 3 minutes). This ensures that the fixer is washed off
the paper surface faster and more thoroughly.This not only
cuts down the final washing time by about 30 %, and in
particular it increases the prints' durability.
If a hardener-fixer is used, the soda intermediate bath is
not recommended. <end quote>
They say "Between fixer and final wash". That's somewhat
ambiguous. Wonder how many washes they have in mind?
"I wonder if the alkalinity would leave the paper
emulsion softer which might make it vulnerable to
some toning processes."
Vunerable? For some a blessing. Something to
consider for those having slow, stubbern to tone
papers. Carbonate's high ph is a concern. Perhaps
Agfa thought that recommendation safe at least with
their papers. Today's hardener incorporated emulsions
may take that high a ph with little effect.
The process has a parallel with ion-exchange water
softeners where a brine solution is used to purge the
impurities made part of the resins used. Emulsion and
paper playing the part of the resins. Dan
Well, I've got plenty of seawater up here in Maine, but this time of the year, it's a little chilly to contemplate taking my prints to the beach to give them a bath.
Originally Posted by john_s
At least the sea water in Maine would be pretty clean, I would think. I would hestitate to put my prints into Port Phillip Bay, just walking distance from here. I suppose if I wanted them toned....
Originally Posted by Maine-iac
Some years ago Prince Charles swam very near here and said it was like swimming in untreated sewerage.