Cyanotypes from English botanist Anna Atkins’ 1843 work “Photographs of British Algae: Cyanotype Impressions.

Cyanotype Invented in 1841, this simple, inexpensive photographic method became popular from the late 19th century to the early 20th century.

This "blueprint", meaning "printing in blue", comes from a printing process, cyanotypy, then diazography and represents a technical drawing used for the construction of the building.