[pure-silver] Re: AW: Re: toxicity
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Fri, 15 May 2009 10:25:26 -0700
----- 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
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.
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.
So, here I am lecturing the teacher.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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