What you see here is 'Cyanotype' photography; a process discovered by John Frederick William Herschel in the 1840s. Herschel inspired his young friend, Anna Atkins to illustrate her botanical studies with cyanotype photograms. Three volumes of her book 'Photographs of British Algae: Cyanotype Impressions, represent the earliest examples of books illustrated with photogenically produced images.
Cyanotype paper is paper coated with a special iron-based chemical. When exposed to sunlight, a chemical reaction occurs and causes the beautiful transformation you see here.