Re: Sodium Bisulfite

Katharine,
      The chemists in the group can answer your question better than I, so
y'all have at it.
     The necessity for a longer wash is in the lit since 1898 (Packham in
Barnet's book). Warren recommends hypo with a long wash (1898, Handbook to
the Gum Process). Maskell says sod bi is extremely soluble so wash a minute
or two (one refute). Sod bi and alum were actually the clears of choice,
alum the most, until the 70's until its archivalness was questioned. Or the
sun, as we have talked about here a year ago. Henney first to say pot
metabi more effective than alum or sod bi in 1939--no mention of the wash
time. Beloved Scopick says this p. 42 and and sources Wm Crawford. Whether
all these authors are repeating misinformation or not, who knows. Maybe
they are using the "smell" test, and the paper still stunk sulfury longer
when using the other clears. I can just about guarantee there is no chemist
who has tested gum prints for this--who would know who cleared with what?
Except maybe the Getty institute is onto it. All I know is I use pot metabi
because I feel confident that a 10 min wash is sufficient therefore. If I
clear.
     Gum was born during a time when there were massive problems with prints
fading, spotting, deteriorating, so perhaps the advice is springloaded. I
know from photographic work over the last 8 years the problems that ensue
from not washing out fixer enough.
     This is as good as I can give you at the moment--do not have time to go
back and check every source for exact wording, etc., so please excuse me if
I have something incorrect, in advance. It is more important that I plan
assignments for a 2D art class that is coming up in 4 hr.
     Most recommend drying the print before clearing. I do both, mostly dry
first, tho.
Chris

> Christina Z. Anderson wrote:
> >
> The reason
> > why potassium metabisulfite is recommended the most is it is very water
> > soluble and thus requires shorter wash times afterwards for archival
> > purposes--10 minutes as opposed to 20-30 or more.
>
> Chris,
> Do you have a reference for this? I've never heard anyone say this
> before; the arguments for using potassium metabisulfite I've seen or
> heard have always been based on it being less apt to soften the gum.
>
> This argument doesn't even make sense to me on the face of it, but I'm
> willing to be enlightened. To me the water soak isn't about something
> going into solution in the water; after all the xsulfite is in solution
> when the paper goes into it, and the paper is still soaking wet when it
> goes from the clearing bath into the water bath. So it's a matter of the
> solution that's in the paper diffusing out into the water, rather than
> something actually going into solution, no? What you're doing is just
> make an already existing solution more dilute, rather than putting
> something that wasn't in solution into solution. So if you've got a
> solution in the paper that's 5% sulfite, or in other words 95% water,
> oozing out into 100% water, why would the sulfite move into the water
> more slowly than say a 5% solution of metabisulfite? I can sort of make
> myself imagine that theoretically the solubility of the material in
> solution might possibly make a slight difference in the speed with which
> the 95% water diffuses into the 100% water, but I'd need to be shown
> empirically that that's the case, and how it could account for the "less
> soluble" bisulfite solution taking 2 or 3 times longer to leach out of
> the paper than the "more soluble" metabisulfite solution does.
>
> At the same time, in my own experience I haven't seen a whole heck of a
> lot of difference, at least between sodium bisulfite and sodium
> metabisulfite, in the inherent solubility of the two.
>
> I did look for the paper Richard mentioned on Ryuji's website that talks
> about the difference between sodium bisulfite and sodium metabisulfite,
> but didn't see it there. And clicking on "photographic chemistry" or
> "notes on chemicals" gave me a "not found" error. (As a matter of
> fact, clicking on anything on the site gives me a "not found" error).
>
> Unfortunately I took solution chemistry as a summer course, five days a
> week-- lecture all morning, lab all afternoon, homework all night. As
> anyone who knows anything about the psychology of learning can tell
> you, this is a surefire way to learn nothing, as time is needed between
> sessions to absorb the information. I can vaguely remember equations
> with equilibrium constants and other gizmos, but I'm afraid I didn't get
> a whole lot out of it. So if someone knows enough about this to explain
> to me why this argument makes sense, I'd appreciate it. Thanks,
>
> Katharine Thayer
>
Received on Wed Aug 25 05:23:13 2004