From: Richard Knoppow (dickburk@ix.netcom.com)
Date: 01/31/03-01:21:25 AM Z
----- Original Message -----
From: "Christina Z. Anderson" <zphoto@montana.net>
To: "Alt Photo List" <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, January 30, 2003 9:04 PM
Subject: self masking and POP
> I've come across a couple books that conflict on self
masking. One book
> says cyanotype is not self masking because the
purple/blue/grey color does
> not hold back actinic light and shadows block up, but that
VDB, platinum,
> and palladium are all self masking (Van Keuren). Another
book says
> kallitypes and VDB are not self masking but salt is, and
hence shadows don't
> get as deep (Crawford). Another says VDB is not self
masking, too (James).
> Who is correct? I think all people agree that platinum is
self masking, but
> how about:
> palladium
> kallitype
> brownprint
> van dyke
> cyanotype
> salt?
> And furthermore, which of these are POP? Cyano, VDB,
salt??
> Chris
>
I can't speak for all the above processes.
There are two mechanisms for self masking, which is simply
the lowering of shadow contrast in comparison to mid tones
and highlights.
The first, and the one which applys to silver POP is the
increasing density of the photolytic silver holding back
further light.
The other is desensitization with increasing exposure.
This can apply to processes which are developed in some way
as well as those which produce an image from the direct
action of light. This isn't exactly masking but has the same
effect of creating a long shoulder. I am pretty sure this is
the mechanism which applies to platinum.
A non-alternative example is a trick using conventional
printing paper. The paper is saturated with developer or
even placed in a shallow tray and exposed to the enlarger. A
partial exposure is given and some time allowed for the
image to begin developing before the exposure is continued.
The effect can be somewhat like POP.
--- Richard Knoppow Los Angeles, CA, USA dickburk@ix.netcom.com
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