U of S | Mailing List Archive | alt-photo-process-l | Re: blue in cuprotype answer

Re: blue in cuprotype answer

Hi Christine
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:

Dear Cuprotypists,
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.

Thanks,Jim Patterson