One Stock Solution Cyanotype

nmp said:

I don't have a mold problem - I might have had some as long as 6 months without it (touch wood...) However, once the 2 are mixed, it becomes blueish in just a day or two. On the other hand, for student work it might still be fine - the blue stains can be removed by washing longer in plain water I suppose. In my case, I "develop" with acidified water so the next day there is a lot more fogging in the print.

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Donald Qualls said:

There might be a difference depending on which of the (several) cyanotype formulae you're using, too. Traditional or one of Mike Ware's several versions.

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Andrew O'Neill said:

. We're using very cheap Stonehenge paper,.

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pentaxuser said:

I was tempted to buy this paper until I saw the primitive dangerous-looking people who made it. All animal skins and clubs
Just didn't fancy my chances if I needed to return a faulty batch

pentaxuser

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Andrew O'Neill said:

I always used to keep solutions A and B separate. After about a week, the ferric ammonium citrate solution would go moldy. I don't make many cyanotypes, so mixing smaller batches didn't help,
A few weeks ago, I started mixing the two stock solutions together. After three weeks, no mold. And solutions are still quite active. Having a single stock solution is better for my students. The simpler it is, the better!
Anyone else using a single stock solution?

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fgorga said:

I have never tried keeping a single (mixed) stock solution.

However, I am not surprised that it does not grow mold. The cyanide in the ferricyanide solution is quite toxic. On the other hand, as we all often see, ferric ammonium citrate (FAC) is a very good culture medium for mold! Two essential elements for living organisms, nitrogen (from the ammonium) and carbon (from citrate), are abundantly present.

Personally, the growth of mold in the FAC solution is not really a problem. I simply filter the FAC solution directly from my stock and into a measuring cylinder. This extra step adds very little time or complexity to the process. Even months old FAC solution with significant growth of mold seems to work just fine... I guess that they don't "eat much"!!!

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Andrew O'Neill said:

I think a single solution for my students will be best. The easier it is for them, the better!

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fgorga said:

As a retired chemistry professor, I fully understand that position!!!

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