Re: pyro developed negs for cyanotype?

Diana wrote:

> But when he tried to print these gorgeous
> negatives, the exposure time (in the light box) was stretching an hour
> or more..and still, he was losing so much, especially in the highlight
> area, and basically getting faint, washed-out images.

> negatives, though "perfect" by my estimation (and not bullet-proof in
> appearance), were just impossible for making a decent cyanotype. He
> then told me, towards the end, that he had developed these in Pyro.

As you pointed out, pyro stains the image. In theory, you get a stain
image that is proportionate to the silver image at each point on the
negative. The color of most pyro stains (it varies depending on the
particular developer and film) absorbs ultraviolet wavelengths, which are
the "actinic" wavelengths for most alt processes (including cyanotype).
Thus, pyro negatives are much denser from the paper's perspective than they
appear to your eye (which tends to ignore the stain, because the eye is
sensitive to the wavelengths that pass through the stain). You can sort of
approximate the effect by looking at the negative through a deep blue
filter, and a densitometer's blue channel gives some idea of how dense the
negative really is for printing purposes.

One further complication is that some films/developers/techniques tend to
generate an overall stain in addition to the image-proportionate stain,
which acts essentially like a neutral-density filter to utraviolet light.
This obviously extends the printing time for UV-sensitive processes.

Best regards,

etienne
Received on Sun Oct 31 13:43:42 2004