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 have remains of two cyanotype formulas on the shelf, my "plain" one has
no mold re-growth on the A after several years. The one with the oxalic,
does.
> Your best bet would be to make up only what you need for a couple of days
> and keep the dry compounds in their respective storage jars until needed.
>
> Tony McLean.
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.
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?
Judy