Re: Chromatype anybody??

Quoting ryberg <cryberg@comcast.net>:

> In his book on cyanotypes Mike Ware mentions but does not comment on a
> process called chromatype. Google has only one pertinent listing--about
> the
> 7th if you just type in chromatype-- which gives a very 19th century
> description of the process (that means elegant prose and vague specifics).
> The process uses copper sulfate, Potassium dichromate, and silver nitrate.
> I have not been able to make it work. Usually I get a smudge of
> orange. Sometimes in the smudge there is a hint of an image. But there
> are
> sometimes nice, intense, brick-red tones too, which makes me want to get
> it
> to work.
> Any advice?

I have had this process working. The resulting images are a rich red colour
on a brownish
background. My notes are at home so working from memory. You need a solution
composed of the dichromate and copper sulphate. This is exposed under a positive
(I did not get the "solarisation" effect to happen, at least not with reasonable
exposure times). I would then brush it with a silver nitrate solution at
which point
the red colour would form. Finally wash in plain water.

I was tackling two problems. One was cleaning the print. I seem to vaguely
recall
that the brown background colour was at least partly due to dichromate stain.
The second and more serious was image permanence. The red colour is a silver
compound of some kind, and I could not make it stable. It seems to react easily
with a range of chemicals. I also seem to recall an image shift with time,
I can't recall exactly, but think it was the red colour "fading:" back to the
a brownish colour. I gave up on the process due to this stability issue.
I suspect this may be why it never became popular.

Richard

-- 
Richard Urmonas