[alt-photo] Re: further cyanotype observations

[Alberto Novo]

> I use 20% A to 8% B 1:1, which if I do the calculations of Alberto's mix/your mix, Loris, I should be at 20%A to 9.6% B so I could up the B a bit. 
> 
> I got tremendous bleeding with 2A:1B and that was when the conversation started a couple years back and Alberto was such a saint to explain it to me why.

I would not add confusion speaking of stechiometry. If one is satisfied with 
his method, I would suggest not to change. Otherwise, like Christina and 
Loris have seen, simply lowering the ratio of citrate to ferricyanide (by 
the mixing ratio of the solutions A and B, or increasing the concentration 
of ferricyanide) will solve any bleeding problem at the expense of the 
exposure time (ferricyanide acts as a filter for UV) and a slight gain in 
contrast and Dmax.
But cyanotype is sensitive to the alkalinity of the paper and of the rinsing 
water, so this is an important variable of the process. Once, I forgotten a 
print in the water and after a few hours it came out almost completely faded 
with a violet/magenta hue. You can achieve the same result in a few minutes 
using a dilute solution of sodium carbonate.
The variations on cyanotype are much more than simply the ratio between AmFe 
citrate and ferricyanide: there are at least 40 patens relying only to the 
chemistry of cyanotype when this was the main process for reproducing 
documents (more or less, in 1930-1940). Among those, there were cyanotypes 
with ferrocyanide (with or without ferricyanide), AmFe oxalate, and amines 
with the aim to reduce the exposure and the developing time of the machine 
process, and increase the stability. 

Alberto 

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