perhaps a good reference about this process is in
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
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).
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
2) Could this be the reason that this process never caught on, that it is
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