[pure-silver] Re: AW: Re: toxicity
- From: Jean-David Beyer <jeandavid8@xxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Fri, 15 May 2009 15:29:05 -0400
Richard Knoppow wrote:
----- Original Message -----
From: "Jean-David Beyer" <jeandavid8@xxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, May 15, 2009 5:00 AM
Subject: [pure-silver] Re: AW: Re: toxicity
Jean-David Beyer wrote:
This is not a new problem. Julia Margaret Cameron, and
early photographer
(1815 - 1879) used cyanide for a fixer even though Sir
John Herschel
pleaded with her to use thiosulfate instead. (She did not
die of cyanide
poisoning.)
I found the quotation: "that dreadful cyanide of
potassium -- letting it run over your hands so
profusely -- Pray! Pray! be more cautious."
As you know a variation of the wet plate process was
used for years to make negatives for photomechanical
half-tone plates. While I doubt if cyanide was used as a
fixer, as it was in the early days of the wet plate process
A friend of mine, who was a photoengraver in the 1970s, said they still used
wet plates in his shop (supplying half-tone plates for NYC newspapers) and
used cyanide fixers for them.
it was used in Monckhoven's Intensifier which also contained
mecuric chloride! Monckhoven's has the peculiar property of
acting as a reducer for low densities and a strong
intensifier for high densities. When used on a half-tone
negative it has the effect of sharpening up the edges of the
dots.
This is true. They used cyanide for a lot of things. Apparently is is a good
cleaner for silver stains too. I would not know. I never wanted either
cyanide or mercury salts in my darkroom, or anywhere else, for that matter.
I am not sure when dry plate stripping film was
introduced for making half-tones but it was certainly in use
by the 1930s eliminating all the hazards and problems with
using wet plates. Many workers thought that the old system
still produced better plates so continued to use it. Later,
perhaps around 1940, Kodak introduced self-screening film
which elimiminated the need for the cross-line screen and
allowed half-tones to be made in any sufficiently large
camera.
True enough, but I never liked the results of the self-screening film, or
even those Kodak half-tone contact screens.
So, here I am lecturing the teacher.
Fine with me. I never claimed to know everything.
--
.~. Jean-David Beyer Registered Linux User 85642.
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