Re: cyanotype question
This is exactly what I am looking for.
My formula is 20%A to 8% B thus a 2:1 is 40%A: 8%B, so by your calculations, anything above using a .92A:1B would promote bleeding--even 1A to 1B would do so, which is what I find in practice.
My guess was always that there was too much of SOMETHING in the formulation that created the runoff, but I never knew what the "something" was until I saw how smooth and non-bleeding the side by sides were with increased potassium ferricyanide. But I wasn't sure I could trust my eyes nor did I know the chemistry reasoning behind the observation.
In Ware's book he defines an average of the two as being a 26% A to a 12% B which would also follow your guess, below--being the most of A that might work with B without bleeding. It would equiv to your formula of 21.6%A to 10%B, comparing apples to apples.
Thanks for this tidbit, it really clarifies things for me.
Maybe an unrelated question--is it **possible** that the bleeding in pt/pd could similarly be caused by an excess of iron?
My calculations are that, for a 10% potassium ferricianide, the non-bleeding equivalence would be a solution of ammoniium iron citrate (green) between 20 and 23%. If so, 25% is in the bleeding range.