"Cyanotype" is a photographic process, discovered in 1842, involving two chemicals (ammonium iron(III) citrate + potassium ferricyanide) and UV light resulting in a beautiful Prussian Blue image.   Simple, beautiful & fascinating. Every year on the last Saturday of September, photographers and artists worldwide will gather in backyards, parking lots, galleries and parks to connect, create and celebratethis antiquarian photographic process.