cyanotype sensitivity

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From: Sarah Van Keuren (svk@steuber.com)
Date: 04/17/00-07:18:59 PM Z


Judy wrote:
But exposure times for VDB & cyanotype are, with any lighting system I've
used, within 20% of each other. Maybe you've got some cockamamie paper?
Try a test of the cyano on a good quality typing paper, or even a paper
bag, to check that..

Judy, I can't believe that you have found vandyke brown and cyanotype
exposure times to be within 20% of each other. My experience has been more
like Gwen's, though not quite so severe. To achieve a cyanotype exposure as
rich as a full-bodied vandyke takes an exposure that is at least 3 or 4
times as long as for the brownprint. I use the most commonly published
cyanotype formula first found in Bea Nettle's Breaking the Rules: 50gr
ferric ammonium citrate to 8 oz. distilled water for A Sol., 35gr potassium
ferricyanide to 8 oz. distilled water for B Sol. (I'm sorry to mix
avoirdupois & metric but that is how it was transmitted.) Perhaps your
formula is faster without being Mike Ware's New Cyanotype formula. I noticed
that my formula was not given in his book, Cyanotype, though he listed many
old ones. I am intrigued by the idea of increasing the amount of A Sol. and
will try it in the sun this summer. Perhaps my pinhole negatives that range
from almost clear to very dense require longer exposure times than your
negatives but still the proportion between the times for vandyke and
cyanotype would remain the same. Maybe light source is the clue. Perhaps
vandyke and cyanotype are sensitive to slightly different wavelengths within
the realm of actinic light and maybe you are using a light source, such as
black light, that is fast with cyanotype but slower with vandyke. I am
basing my comments on observations made during over twenty years of
sunprinting and also using various platemakers. I don't even bother using my
sunlamps for cyanotype.... In the sun, middle of day, a strong cyanotype
only takes about 10 minutes even with my negatives but that could easily
translate to an hour with a slow exposure unit like Gwen's.

Sarah Van Keuren


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