From: Katharine Thayer (kthayer@pacifier.com)
Date: 02/24/03-02:55:59 PM Z
On reflection I don't think it's so surprising that I said one thing
when I was thinking of sodium bisulfite in its use as a clearing bath,
and something a little different when, as I now recall, a number of us
were casting about for solutions to a problem where someone had printed
a layer of gum on top of a platinum print and wanted to take the
hardened gum off. In order to recapture my exact thinking I'd probably
have to go back and look at the post I was responding to when I said
this, but please don't send that one to me too, this is taxing my brain
too much already trying to explain something I said some time in the
past, in a different context, and I don't want to spend any more time on
it. The point is that, as I said earlier this evening, when used for a
clearing bath, sodium bisulfite probably does soften the gum a little,
but not enough to make it float off or anything. I'd certainly never
seen a problem with it as a clearing bath, or I would have changed
compounds. But it would also probably, as I said in the discussion
months ago about removing hardened gum, soften the gum enough that you
might be able to scrub it off with a brush if you really went at it. So
both things are true. But as for the relative strength of sodium
bisulfite relative to potassium metabisulfite, I was obviously relying
on other sources (cf my phrase "by all accounts") probably including
Livick himself, for that information, because I've never used the
potassium metabisulfite myself.
Katharine
Christina Z. Anderson wrote:
>
> Shoot; OK, this is the quote:
> "The clearing step is intended to remove dichromate residue, not hardened
> gum, but as a matter of fact sodium bisulfite does soften the hardened gum,
> too. The "various sulfites and sulfates" which clear dichromate stains have
> different qualities, being different compounds, and while they may be
> roughly interchangeable for the purpose of clearing dichromate stains, they
> are not interchangeable in all respects. Sodium bisulfite, by many accounts,
> is the strongest and most likely to soften and lift the hardened gum, which
> is why I recommended it for gum removal, and why something like potassium
> metabisulfite, which removes dichromate stains but isn't so likely to
> disturb the hardened gum, would not be useful removing hardened gum. Sodium
> bisulfite, having rather strong fumes, should be used outside or in a
> well-ventilated area."
> ----- Original Message -----
> From: "Katharine Thayer" <kthayer@pacifier.com>
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Monday, February 24, 2003 11:08 AM
> Subject: Re: gum printing
>
> > Christina Z. Anderson wrote:
> > >
> >
> > > I also notice Livick uses a 1% pot metabi clear, because it doesn't
> > > soften the gum like sod bisulfite, which is what you, Katherine, said a
> > > while back.
> >
> > I said that? I don't remember saying that, and without context, I don't
> > know why I would have said it, since in my own practice, I haven't found
> > that sodium bisulfite softens the gum appreciably, once it's been
> > hardened. I mean it probably does a little, but not enough to be an
> > issue, certainly not enough to change clearing agents over. Since I
> > haven't used a clearing agent much, my experience probably isn't enough
> > to judge by, but I've never had the image softened or lifted by the
> > sodium bisulfite.
> >
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