Cyanotype is an antique photographic process distinctive for producing Prussian blue monochromatic prints. Developed in the mid-19th century, cyanotype was quickly embraced as an inexpensive method for reproducing photographs, documents, maps and plans (hence the enduring architectural term "blueprint").
Famously, it was also used by Ana Atkins and other field biologists for indexing plant specimens - the first photograms ever made!
Cyanotype is a remarkably simple process that employs two inexpensive chemicals and sunlight/UV. Prints can be made on any natural fiber: paper, cotton, silk, wool, wood, etc.