[pure-silver] Re: Negative Intensification
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Wed, 2 Dec 2009 16:15:54 -0800
----- Original Message -----
From: "Ralph W. Lambrecht" <info@xxxxxxxxxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, December 02, 2009 2:48 PM
Subject: [pure-silver] Re: Negative Intensification
Tim
Selenium is a proportional intensifier, meaning same
percentage for
highlights and shadows. You may not want that, because it
will
increase contrast by doing little (in absolute terms) on
the shadows
and lots in the highlights. You probably would like a
sub-proportional
intensifier, but unfortunately, the chemistry for that is
quite toxic.
I think, Richard has posted the formula before, but I can
look it up
if you are interested.
Regards
Ralph W. Lambrecht
http://www.darkroomagic.com
There are a number of intensifiers in the literature.
The problem with most of them is that they can destroy the
negative. Selenium is one of the least hazardous in this
regard but has a relatively limited amount intensification.
However, Selenium has the advantage that the intensified
images are permanent where they may not be with other
intensifiers.
Note that if there is little or nothing in the low
density areas no intensifier will produce detail there. In
fact, high contrast printing paper will bring out whatever
an intensifier will but will also exagerate any blemishes or
lack of uniformity in illumination.
I rather think Ralph is thinking about Monckhoven's
Intensifier. This contains two of the most toxic substances
around: meruric chloride and potassium cyanide. In fact
despite its effectiveness it is useless for pictorial
negatives because it is simutaneously an intensifier for the
high density areas and a reducer for the low density areas.
Its original purpose was to sharpen up the dots on half-tone
negatives made by the cross-screen method.
All intensifiers serve to increase contrast. Again, if
there is nothing in the shadows no intensifier will do any
good.
I think by refering to Selenium as proportional Ralph
may be confusing the effects with reducers which come in two
or three forms, proportional, super-proportional, and
cutting. Proportional reducers affect all densities and have
the effect of lowering overall density without affecting
contrast too much. They are used for overexposed but
normally developed negatives. Super-proportional reducers
affect the high densities more than the low ones so reduce
contrast as well as average contrast, they are used for
overdeveloped negatives. Cutting reducers affect shadow
areas more than dense areas and are used for cleaning up fog
and similar effects. I am unaware of any such choice with
intensifiers.
--
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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