U of S | Mailing List Archive | alt-photo-process-l | Re: Cuprotype

Re: Cuprotype

perhaps a good reference about this process is in http://www.usask.ca/lists/alt-photo-process-l/200710/msg00135.html
There is also a description of the chemical mechanisms involved in the formation of the image.
I have not yet tried this process, but I may argue that your blue hue developing with time might be prussian blue due to iron left by an insufficient clearing. This is also in the Troubleshooting section of the article above.
As for the chemistry, if the description of the article is too complex to you, it can be resumed as:
1) iron(III) is reduced to iron(II) by light;
2) iron(II) reduces Cu(II) to Cu(I) and copper(I)thyocyanate is formed;
3) iron is removed by thyocyanate (blood-looking compound);
4) ferricyanide oxidizes copper(I) to copper(II) and the resulting ferrocyanide reacts forming copper(II)ferrocyanide (brown).

Hi All
So I have now made several attempts at making Cuprotype prints using Jim Patterson's formula that Christina posted in October. I have had varied results and a near disaster(that's another story). The resulting colour tone is a wonderful terra cotta red when I used BFK paper and a not quite, but still good, colder tone when I used Plantine. The dmax is good when it is wet but is too low when it dries. I have not tried to double coat or adding ammonium dichromate to bring that up but I have another problems that are more pressing. The problem is that the print is getting an overall light blue stain (some times not so light) after as short a period of 3 days and as long as 3 months. It looks fine after it has been dried and than after a period of time it quickly goes blue. It tends to be relatively even over the white paper surface, front and back. In order to stop this problem I increased the clearing bath from a total of 4 min to 8 min with 3 baths, always with fresh chemistry. I also went from the 3 changes of wash baths as recommended to 30 minute wash time. One of the prints that I did I washed for 2 hours and it still had a light blue tinge.
So my questions are
1) Is anyone else trying this process and have they experience and similar problems?
2) Could this be the reason that this process never caught on, that it is not stable?
3) I am not a chemist but can some one explain to me in layman's terms how this process works. It is not like other photo processes, with this you coat the paper than develop that paper until the image disappears, than you "clear" it with the developer that has been diluted(what's that going to do). The blank paper is than put into a strong bath of chemicals which is normally used as a bleach and a photograph appears and than you wash it in water. Is that magic or what.
Thanks for any help