Re: blue in cuprotype answer
Thanks for your reply. It seems that the last paragraph may be the
answer to my problem. It describe exactly what is happening to my
prints, so I will try the citric acid. I just posted a print at
hybridphoto so if you get a minute take a look
Thanks and good luck with your other tests. Too many processes and
not enough time.
On 20-Jan-09, at 6:40 PM, Christina Z. Anderson wrote:
Below is the kind and detailed answer I got form Jim Patterson, the
originator of the cuprotype process I posted on the list some while
ago. Maybe it will help with the problem of bluing out?
I am busy with chromoskedasic testing and gum so it'll be a cold
day in hell before I get to cuprotype so enjoy his notes and post
some work online please!
Christina Z. Anderson
Hi Chris, Good to hear from you. Here's some info that may help.
The first image formed in the developer is copper (1) thiocyanate,
and the citric acid in the developer is to help mobilize the iron
out of the paper. The clearing bath is diluted developer to have a
small amount of thiocyanate to keep the copper thiocyanate
insoluble by common ion effect, and the citric acid helps remove
the iron. Adding more citric acid to the clearing bath will help
remove the iron better, but if it is too high it may remove part of
the copper thiocyanate image. I toyed with the idea of making a
separate clearing bath, which may be more effective, with a small
amount thiocyanate and more citric acid, but I was trying to avoid
more solutions and keep it simpler. Example: Clearing Bath: 0.1 %
ammonium thiocyanate and 1 % citric acid. If you don't clear the
iron salts out of the paper, when you add it to the toner
(potassium ferricyanide), any iron immediately reacts with the
ferricyanide to cause a permanent blue stain. Use distilled water
for the clearing bath to avoid iron in tap water.
The WASH of dilute acetic acid is to remove the ferricyande toner
out of the paper. If ferricyanide is not removed from the paper,
it auto- decomposes after some time to iron ferricyanide, the blue
stain. If your tap water has iron, use distilled water. Also a 1%
citric acid wash may work better than the acetic acid wash.