How long can you leave a surface painted with cyanotype solution before exposing it to U.V. light, if it is kept in a light proof bag?


Given the fact that presensitized cyanotype ("sun print") papers are sold commercially, it seems that at a minimum coated and dried cyanotype sensitizer can be stored for at least several months.

In practice, the limitation will be on how rapidly either stray UV or other environmental factors prompt the reaction between the ferricyanide and the ferric ammonium citrate (presuming traditional cyanotype). If thoroughly dried without heat and kept in a thoroughly dark storage environment, this rate is very slow.

For home sensitized paper, I've kept it only a few days before exposing, but I've read of people keeping it for at least a few weeks. Few who coat their own will do so in quantities requiring much longer storage, but it seems it's possible -- with the proviso that commercial precoated paper may have a slightly modified sensitizer compared to the traditional Herschel formula from the 1820s.

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