Re: Sodium Bisulfite

Hi Giovanni,
I answered the question about what did I think caused your yellow stain
that wouldn't clear, which I thought was the important question, but for
further reference:

gdimase@hotmail.com wrote:
>
> Hi Katharine,
> I assume the sodium bisulfite is on a 12% concentration.

Actually 5% works fine for sodium bisulfite.

> How much time you put the picture in the bath?

It starts clearing immediately, is usually completely white within 10
minutes.

> An the you bath it again in a water bath, for how long?

15-20 minutes?

> What about stubborn cases? You keep it longer?

Yes, a bit (20 minutes?) but in such stubborn cases the stain will be a
very distinct blue-green-with-brown-overtone, not yellow at all. This is
one reason I feel I can say with some confidence that a yellow stain
that won't clear right away is almost certainly pigment stain, not
dichromate stain at all, and why I wish there were a different name for
dichromate stain that would reflect the fact that dichromate stains, at
least in my experience, are almost never yellow.

I take it on faith from Pete Frederick that an extreme stain can
require 1% sulfuric acid to clear, but I've never seen a stain that
stubborn myself.

Katharine Thayer

> Let me give you a recent example of what happened to me:
> I was working on a full color print, this picture has an open clean white
> sky therefore the negative section of the sky is totally black.
> I did my first cyano print and everything was fine (sorry I sized the day
> before first with gelatin and glyoxal).
> I go next day for my Blue channel and yellow pigment and the sky comes out
> "yellow", I thought it was stained, next day I did my Green channel and
> magenta pigment and I got a beautiful picture but with the yellow sky (as I
> said out of a black negative).
> I wash it with sodium bisulfite and the stain is still there.
> Yes, I know I can create a new negative and paint the sky on white but I
> want to know what may have happened.
> Thanks,
> Giovanni
> ----- Original Message -----
> Wrom: ZRCLBDXRQBGJSNBOHMKHJYFMYXOEAIJJPHSCRTNHG
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Saturday, August 21, 2004 12:13 PM
> Subject: Re: Sodium Bisulfite
>
> > Martin Angerman wrote:
> > >
> > > The sulfite acts as a reducing agent. It clears the dichromate by
> reducing
> > > it to an inactive form.
> >
> > Hmm. I've always wondered just what a clearing agent does, chemically,
> > but this explanation doesn't work very well for me, since what is called
> > "dichromate stain" in my experience almost always consists of Cr+3 not
> > Cr+6. I tried a few years ago to introduce a new name here for the stain
> > to reflect this reality, but had little luck with this campaign and gave
> > it up after a while.
> >
> > Except for unusual cases where a peculiar combination of sizing and/or
> > paper hangs onto the bright yellow dichromate and won't let it go, the
> > hexavalent dichromate, being very soluble, almost invariably washes out
> > in the developing water without additional clearing needed. It's the
> > less soluble reduced chromium species that comprise a tan, brown, or
> > green stain that must be removed to clear the print. I don't know what
> > the clearing agent does to the reduced chromium to get rid of it, but
> > the point is that the chromium in the stain is already reduced before
> > the clearing agent is introduced, and that we've just confused ourselves
> > by calling this reduced-chromium stain a "dichromate stain."
> >
> > It's true that the same clearing agent works for both the less typical
> > dichromate stain and the usual reduced-chromium stain, (except for very
> > heavily overexposed prints that are so stained that sulfuric acid may be
> > needed to clear them) but I'm not sure what that means in terms of what
> > happens chemically.
> >
> > At any rate, my own experience is that sodium bisulfite can be re-used
> > many times without diminishing its effectiveness. I had a gallon of it
> > mixed up years ago that I used for 3 or 4 years before it stopped
> > working. I only need to clear very occasionally, so the number of
> > prints that were cleared with that gallon over the 3 or 4 years was
> > rather small, perhaps 12 or 15 at the most, but it would have been a
> > waste of materials and money to mix up new stuff each time, when the old
> > stuff was fine for re-use.
> >
> > You know you need a new batch when the solution loses its pungency of
> > odor; in my experience that happens comcomitantly with loss of ability
> > to clear effectively.
> >
> > I no longer keep a big jug of clearing agent around, because I've
> > learned that immersing the paper in the clearing bath is only necessary
> > in odd cases such as the sizing/paper problem mentioned above or when
> > I've accidentally spilled some dichromate on the coating table and not
> > noticed it and it's soaked into the back of a piece of paper. But for
> > simply clearing an image, I've found that simply brushing the clearing
> > agent on the image works well, and then a short dip in water is all
> > that's needed to rinse it out of the print, whereas when the paper is
> > immersed, you need a more extended soak to make sure you've got the
> > stuff out of the paper. So now I just keep a pint mixed instead of a
> > gallon, but that pint is as fresh and effective today as it was when I
> > mixed it months ago; the extra air in the liter bottle that I keep it in
> > doesn't seem to affect it at all.
> >
> > Katharine Thayer
> >
> >
> >
> > >
> > > Air can also oxidize sulfite to sulfate, ruining it as a clearing agent.
> > > Therefore, I would not recommend storing it for more than a day. Going
> from
> > > Saturday to Sunday would probably be OK, however.
> > >
> > > My thoughts would be similar to reusing glyoxal and over-using fixer.
> The
> > > sulfite (and others) are relatively cheap, particularly compared to your
> > > time and other materials. How many people would dilute platinum salts
> or
> > > short a mixture of good pigment in gum printing, just to save money?
> The
> > > same applies to the rest of the process.
> > > ----- Original Message -----
> > > Wrom: SWZIDREXCAXZOWCONEUQZAAFXISHJEXXIM
> > > To: "AltPhoto" <alt-photo-process-l@sask.usask.ca>
> > > Sent: Saturday, August 21, 2004 7:06 AM
> > > Subject: Sodium Bisulfite
> > >
> > > > After clearing a 2 or 3 gum prints, is the sodium bisulfite solution
> > > > storable for later use or should I just dump it and make a new
> solution
> > > > when needed? Thanks.
> > > >
> > > >
> > > > Darryl M. Gage
> > > > Forestville, NY
> > > >
> > > > "Strange and beautiful are the stars tonight..." Blue Rodeo
> > > >
> > > >
> >
Received on Tue Aug 24 11:37:00 2004