Re: clearing dichromate stain
P.S. I called my sister this morning per our usual Saturday custom;
she wasn't home so I talked to her husband for a few minutes. He
said, "I'm writing an e-mail to express my annoyance about
something." I said, "Funny, I've just done the same thing." He said
his was about difficulties in selling his parents' home, and asked
what mine was about. I said, "Well, as a matter of fact, mine was
about potassium metabisulfite." We laughed, but since he's an
analytical chemist, he was curious what could be annoying about
potassium metabisulfite. I said, "Well, this person thinks that
potassium metabisulfite is 'infinitely better' than say potassium or
sodium bisulfite for clearing dichromate stain, because potassium
metabisulfite is more soluble and therefore it washes out of paper
faster." He said, "Hunh? That makes no sense." I said, "Exactly."
Since there doesn't seem to be much point in prolonging this
discussion further, I won't.
Katharine Thayer
On Jan 6, 2007, at 10:10 AM, Katharine Thayer wrote:
On Jan 5, 2007, at 8:47 PM, Christina Z. Anderson wrote:
Katharine,
I seem to have misplaced the original email you sent, but thought
these points would clarify:
1. I answered Henry with a list from 1898 to present day of all
the clearing methods. In no way was this list an endorsement of
alum.
I wasn't assuming you were endorsing alum; I was simply asking
"infinitely better than what?" in response to your statement "I use
potassium metabisulfite, finding it infinitely better." Better
than sodium bisulfite? Better than alum? That was all I was
asking. All the information I've seen from chemists here, as well
as my own observations, give me to believe that the bisulfites and
metabisulfites are interchangeable. And as you say, alum isn't
seriously considered as a clearing agent now, so it wouldn't be
terribly useful to say that potassium metabisulfite is infinitely
better than alum. So, infinitely better than what? That's all I
was asking.
It was to show the substances in use throughout gum's history. In
fact, if you read the list carefully there were contradicting
statements on there from the various sources.
Yes, I'm quite aware that the historical compilation is full of
contradictions,, factually inaccurate statements, and outdated
recommendations, and as a result I'm not sure I see its utility for
present day workers.
3. When I used to clear, I used potassium metabisulfite. It is
speedy--you can see it by dipping half a print in it and see the
immediate change.
This is also true of sodium bisulfite; they work the same in my
experience.
I also did Livick's method of spray bottle pot metabi and it was
fun to watch.
But did you compare it with sodium bisulfite?
It also rinses out of the paper easily and well, being more
soluble than others. But we hashed that topic out on this list a
year or so ago I think and I don't feel it needs to be rehashed
again. If you search under Alberto Novo he had some great input
on the topic. If I remember correctly, you didn't agree with him
or me at that time.
I did search under Alberto Novo, and found nothing about the
solubility of potassium metabisulfite ; all I found from Alberto
relating to the subject of clearing agents was a discussion about
whether sulfite can work for clearing, which is a different issue.
It was a fascinating discussion, and well worth re-reading.
Alberto and I had a lively conversation (you didn't appear in that
thread for me to agree or disagree with) that makes me nostalgic
for the good days of the list, when we had such open discussions,
but when we did our tests and compared them, our results were very
similar. What our experiments showed together was that if you
treat a stain with sulfite, it will turn the stain from brown to
blue-grey just as bisulfite does, but it takes longer. In my test,
after an hour in sulfite the stain was the same pale shade of blue-
grey as after five minutes in bisulfite, but in Alberto's test the
sulfite-treated stain was a slight shade darker blue-grey than the
bisulfite-treated stain after an hour. One can assume that the
slight difference probably has something to do with the pH of our
water. But as I said, that's a different issue.
But then I searched on "potassium metabisulfite" without
reference to Alberto Novo, and came up with a discussion in which
you asserted that potassium metabisulfite is more soluble than
sodium bisulfite and therefore requires a shorter wash time, the
same assertion you repeat above. When I asked for evidence or a
source for that assertion, it was
traced to Scopick, with no experimental findings of his own or
citation to other findings to back it up; on the basis of such
lack of empirical support I did say I would need to be convinced
that relative solubility has anything to do with wash times. No
scientists or others on the list weighed in on the assertion that
metabisulfite will wash out of paper faster than bisulfite, so I
asked a physical chemist I was working with about this; he
replied, as I reported back to the group at the time, "You are
quite right that the solubility of the compounds in water cannot
be a factor in washout times for the solutions." And since a
metabisulfite becomes a bisulfite in solution, like I said
before, I would need to be convinced with some persuasive evidence
that there is a difference in washing ease or washing speed. So I
find the statement that this topic was "hashed out," implying that
the hashing decided the issue in favor of the idea that
metabisulfite washes out faster, rather puzzling. As far as I can
tell from following that discussion from beginning to end, Alberto
Novo didn't participate in that discussion, so I also find the
reference to Alberto Novo rather puzzling.
I'm sorry; sweeping categorical statements ("potassium
metabisulfite is infinitely better") that I can't see a factual
basis for raise my antenna, and then when I'm sent for proof of the
assertion to a discussion where no one offered support for the
assertion, then there's this red flag. Maybe you're talking about
a different discussion, or different information from Alberto Novo,
that the search engine didn't bring up for me, in which case it
would help if you could be more specific.
Katharine
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