Re: Cuprotype
Hi Alberto
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.
I also thought it could be a clearing problem and that is why I have
always used freshly made chemicals and doubled the clearing time but
that didn't seem to make a difference. I have also increased the wash
time in case it is the toner that is not being cleared. It still
could be the clearing time and I am just having trouble clearing the
Iron out of this paper. I was also wondering if I have Iron in the
wash water. I live in a large city and have been using tap water for
the final wash. I may try increasing the clearing time and see what
happens. I could also shorten the clearing time to see if it
increases the problem. One of the problems is that it takes so long
to find out if it will stain.
Thanks for your input Alberto, it is clear that I need to go back to
my darkroom for some more testing and maybe pull out my high school
chemistry books. I hope that you get a chance to try the cuprotype
process it does produce an incredible red tone print.
Bruce
On 18-Jan-09, at 12:03 AM, Alberto Novo wrote:
Bruce,
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).
Alberto
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
Cheers
Bruce
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