From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 06/15/01-05:48:17 AM Z
shannon stoney wrote:
> Hi. Another cyanotype question, which may apply to other processes as
> well. I have been using the sun to expose my cyanotypes. When there are no
> clouds, the exposure takes about three minutes, and I get about eight steps
> on the step tablet. But, if it's cloudy, the exposure may take seven to
> eight minutes, and I get more steps! Has anyone else observed this
> phenomenon?
What I have found with Pt/Pd may or may not be what happens with
cyanotype.
Rather than the direct sun or shade, the spectrum of light, the nature
of clouds, I have found that the exposure time (not the exposure amount)
can make a difference in contrast. The longer time gives a lower
contrast. I do not know why this happens, but I have noticed it to
happen every time, but I have not quantified how much contrast is
altered for how much exposure time under what conditions and with what
materials or if this effect is consistent. Only that one should expect
less contrast with more exposure time.
I had first realized this in a situation of trying to increase contrast
from a deficient negative. As contrast agents were increased, more
exposure would be required and the exposure time would lengthen, and the
expected gain in contrast would not occur. I also found that printing
in the shade of a tree would not only reduce the sharpness, but the
contrast as well. (I also suspected there can be some other appearances
in the print due to the spectrum of the light, but this is yet to be
researched.) I later found that by lowering the intensity of the light
(by moving printing frame further from the lamps) would produce less
contrast. I have used this shortening or lengthening of exposure time
on occasion to adjust contrast, but really only as a last desperation
attempt. Usually I try to individually process each negative to get
what I want. And, it is easy and controllable to increase contrast with
agents in the coating or developer. However, this is an important tool
to have as there are many ways to increase contrast and only a few to
lower it.
Another way to have control over lowering contrast is to typically
include a contrast agent in the standard coating, then reduce it when
desired. Although there are trade offs for doing this as well.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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