Re: pyro developed negs for cyanotype?

Ah...thanks so much, Etienne. I will pass this along to the man w/the
negatives. I have never developed with Pyro, and the negatives
certainly didn't appear dense to me--not thin--but certainly not dense
to the eye. There were students in the class using 70 year old family
negatives that looked bullet proof to me...and they were having no
problem. Anyway...this explains it well. Thanks again.

Diana

On Oct 31, 2004, at 2:43 PM, Etienne Garbaux wrote:

> 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 13:58:20 2004