>In my experience (and that of my students) the mold doesn't matter. It's
>not attractive of course, but you can just pluck (or filter) it out, and
>the emulsion works the same as ever. It doesn't seem to return after the
>first crop, or at most the second. Or doesn't in the formula I use,
>which is the fe am cit & potassium ferricyanide alone, without added
>oxalic, or dichromate.
I used to filter off these growths too, but I was getting some
unpredictable results. Often I would get a print with blue shadows and mid
tones but with "pink" highlights, which was not unattractive on some
images! Obviously, these mould growths need to feed and excrete so must be
depleting and contaminating the f.a.c. solution to some degree. Still, if
filtering works for you then it must be the water on this side of the pond!
>Some people do like the "prep work," for getting into the proper frame of
>mind, but in my book it's a big pain, not to mention the extra handling of
>dry chemicals... One of the great virtues of cyanotype is how quick, easy
>and direct it is. Having to mix each "couple of days" would cut into that.
>Also, mixing in smaller amounts, any inaccuracy is a greater percentage of
>the whole. If you mix the full formula, you probably don't use that in a
>few days, so end up throwing it down the drain. The alternative would be
>continuing differences in measure (10%?, 20 %?) of the smaller batch,
>possibly, or probably.
Yes, I agree mixing chemicals is a chore and personal safety is an issue
here as well, but it is not exactly onerous. Maybe, I am just paranoid
about slimy moulds invading my sensitiser. With Cyanotype I have found that
the "exact" proportions of pot. ferri and f.a.c. make very little
difference to the final image. The ratio of 3 : 1 can be measured out with
spoons if desired if a chemical balance is not at hand.
>But here's a question for the chemists... we've had some trouble with
>ferric ammonium citrate of late, that is, batches seem quite different,
>and last year at school we had several bad batches in a row. Is there any
>difference in keeping quality, between keeping it in solution or as the
>dry powder? Or is that something you can't predict?
Yes, I have encountered similar problems with ferric ammonium citrate and
would welcome comments from the academics. Cyanotype is, after all,
supposed to be the easiest and cheapest of the "alternative processes" yet
sometimes I find that it can be incredibly frustrating!
Tony McLean.