Re: Sodium Bisulfite

From: Katharine Thayer ^lt;[email protected]>
Date: 08/25/04-05:06:13 AM Z
Message-id: <412C7294.76C2@pacifier.com>

Christina Z. Anderson wrote:
>
> 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. Scopick says this p. 42 and and sources Wm Crawford.

Hi Chris,
Actually, Scopick cites Crawford for the assertion that chrome alum
"threatens image permanence," not for the assertion that potassium
metabisulfite is more soluble than sodium bisulfite and therefore
doesn't require such a long wash time; that latter assertion is made
with no citation to sources.

Crawford was my bible when I was teaching myself gum printing, and I was
thinking that if this assertion was in there and I never noticed it in
all my poring over that book, then I'd have to eat crow over my
assertion that I'd never seen this idea before. (I have Scopick in my
library but have never spent much time studying it because I discovered
it long after I'd perfected my own gum process.) So I had to look up
Crawford to see if I was wrong, but thank goodness, I'm in the clear on
this one. Crawford does indeed say "Alum is often mistakenly
recommended but should not be used because it threatens image
permanence" exactly as cited and quoted by Scopick, but Crawford is not
responsible for the assertion about the relative solubility and wash
times of sodium bisulfite vs. potassium metabisulfite; he simply says
you can use either: "You can clear the print in a 5% solution of
potassum metabisulfite or sodium bisulfite." Nothing more.

 Whether
> all these authors are repeating misinformation or not, who knows.

Well, I only see two in the above mini- lit review that actually make
the assertion about the relative solubility and required wash times of
the two: Henney and Scopick (ignoring the mistaken citation to
Crawford). Scopick (I don't have Henney so can't comment on that)
offers no reference or experimental findings to back up the assertion.
And if it's a fact as you say that sodium bisulfite was the favorite
next to alum until the 70s, the assertion must not have carried much
weight among practitioners of the time.

I wonder what the percentage is that use one or the other today.

<snip>
  All I know is I use pot metabi
> because I feel confident that a 10 min wash is sufficient therefore. If I
> clear.

Well, I guess I need more, some experimental data that show this
clearly, before I feel at all confident that there's a meaningful
difference between the two in terms of practice. As I say, I need to
clear so seldom that it's not much of an issue for me, but it sparks my
intellectual curiosity.

Katharine
Received on Wed Aug 25 12:02:08 2004

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