Re: dichromate stain

Katharine Thayer wrote:
>
> Keith Gerling wrote:
> >
> > Clay says:
> >
> > "Maybe the chemists in the crowd can put forward a hypothesis as to why iron
> > rich water would be more likely to induce dichromate stain."
> >
> > My well water is loaded with iron. It is yellowish coming from the tap, and
> > turns orange when it sits for a couple of days. And I get no dichromate
> > stain.
> >
>
> And there goes another one,
> kt

Look, I'm being somewhat flip about this, but let's get serious for a
minute, since people have been throwing black and white swans around a
lot here lately and getting black swans and white swans mixed up in a
way that's likely to confuse people. So here follows a short lesson in
swans (I like to think I"m entitled to do this because I have been a
teacher of this kind of stuff):

When several people seemed to be agreeing that iron in the water might
be a cause of dichromate staining, and Keith knocked down that idea with
his observation, it's KEITH'S observation that's the black swan. Someone
the other day was making an argument about black swans that, translated
to this case, would say that the person who said earlier that it was the
iron could come back and say, "well, yeah, I still say it's the iron"
and that would be a black swan. No, it doesn't work that way. Keeping
something on your list of candidates for cause of something after it's
been knocked out of the running by contrary observation is not the same
as identifying a black swan, it's not anything like. It's clear at this
point that when people have assumed it's the iron, it's either something
else entirely that got misattributed to the iron, or it's perhaps the
iron in interaction with something else, but it's not the iron by
itself, or it would cause dichromate staining wherever it occurs,
regardless of whatever else is going on.

I don't know, but am willing to bet in the absence of knowledge, that
one nameless gum printer still teaches that ammonium dichromate is no
good for gum printing because it causes dichromate staining, even though
my career of printing with ammonium dichromate and no stain proves that
pronouncement wrong. When I told him that, his answer was, as a couple
of people were hinting the other day, that of course I get dichromate
stain and I'm just in denial about it.

My observation is the black swan (not the only one I'm sure) that proves
his assertion wrong. To argue that his observation (that in his practice
ammonium dichromate causes dichromate staining) is the black swan that
proves that my assertion that ammonium dichromate in and of itself
doesn't cause dichromate stain, would be ridiculous, and would show a
certain lack of understanding of the issues, but that's the kind of
argument that has been made here several times lately.
Katharine
Received on Wed Jun 16 11:18:00 2004