Worth noting that Potassium Ferricyanide, one of the two active chemicals in this process, is quite toxic and poses significant environmental hazard [1]. I might suggest Anthotype [2] instead, which is just Vodka, Turmeric, and Borax. The resulting print is a lovely red/orange rather than blue, and there's significantly less concern over chemical cleanup & disposal. Also the exposure is long enough that you don't even need a dark room!

[1]: https://pubchem.ncbi.nlm.nih.gov/compound/Potassium-ferricya...

[2]: https://www.youtube.com/watch?v=gmQxqE61lOg