RE: Van Dyke washing

Citric acid will dissolve the unexposed iron sensitizer very effectively
- I personally think it's the best tool for the job (that is: clearing
the Vandyke print).
 
Cyanotype and Vandyke images are very different (Cyanotype image forming
compound is Prussian Blue - don't remember the exact name of the
compound - whereas Vandyke image is formed by colloidal silver). That
comment was made about Cyanotype, not Vandyke.
 
Also, it doesn't matter if Citric Acid is harmful to the silver image
"in long term" since you will be washing it out of paper in subsequent
processing steps; 1) rinsing in water after clearing -> 2) toning
(optional) -> 3) fixing -> 4) final wash... in fact, you use it in the
first step.
 
IIRC, that comment was made because there's the risk of citric acid
molecule (a small one) being trapped inside of the prussian blue
molecule (a large one). (The original comment is very Cyanotype
specific.)
 
One of the conclusions of our last correspondence with Mike Ware was:
clearing in citric acid is good for Vandyke, Kallitype (and maybe
Argyrotype) because you can get rid of iron -> which will eventually
fade (oxidise) the silver image.
 
Hope this helps.
Regards,
Loris.

-----Original Message-----
From: redman [mailto:redman@elmet15.freeserve.co.uk]
Sent: 12 Nisan 2006 Çarşamba 18:34
To: alt-photo-process-l@usask.ca
Subject: Van Dyke washing

I have been away from the group and alternative photography for a while.
I am now geting back into the Van Dyke process. After some
experimentation and reading the various bits of advice from this group,
I have settled on Fabriano Artistico paper and two coats of sensitizer.
This seems to produce satisfactory results. But I am now in a quandary.
 
Recently, I note that both Loris and Joe recommend the use of Citric
Acid in the initial rinse bath. However, following Peter Marshall's link
to a Cyanotype website
(http://photography.about.com/library/weekly/aa061801d.htm) I came
across the following statement :
 
"Since Prussian Blue is unstable in alkali, it is essential to keep the
water used to 'develop' the cyanotype at least slightly acid. As most
tap water is slightly alkaline, and you should add a few millilitres of
dilute hydrochloric acid (still sold in some hardware stores as
'muriatic acid') to a bucketful to use. Other acids such as nitric acid
can also be used, but it is best to avoid oxidisable organic acids such
as citric or tartaric acid, which can later break down the image."

Does anyone know if the same advice re citric acid applies to Van Dyke ?

Bob Redman (UK)
Received on Wed Apr 12 09:54:03 2006