These beautiful cyanotypes of marine algae, or seaweed, are remarkable for two reasons. They're from the first book ever produced entirely by photographic means. And they're the first photographic works ever made by a woman.
British botanist and photographer, Anna Atkins' (1799-1871), created Photographs of British Algae—a landmark in photography and publishing—in 12 parts between 1843 and 1853. These come to us now thanks to the New York Public Library, owner of the most complete of only 13 known copies of Atkins' book, scanned and posted online in their Digital Gallery:
"The difficulty of making accurate drawings of objects as minute as many of the Algae and Confera, has induced me to avail myself of Sir John Herschel's beautiful process of Cyanotype, to obtain impressions of the plants themselves," explained Anna Atkins in October 1843.
Through her father, scientist John George Children (1777-1852) whose Royal Society circle included William Herschel and William Henry Fox Talbot (1800-1877), Atkins was aware of the group's experiments with photography. Talbot's "photogenic drawing" technique involved placing a flat object against a light-sensitized sheet of paper (sometimes pressed beneath a sheet of glass to prevent movement and ensure a sharp image) and exposing it to sunlight until the area around the object began to darken. Herschel devised a chemical method to halt the darkening and "fix" Talbot's silver-salt image—the basis for all photography until the digital era.
Hershel experimented with other light-sensitive metal compounds in addition to silver, and in 1842 discovered that colorless, water-soluble iron salts, when exposed to sunlight, form the compound known as Prussian Blue; unexposed areas remain unaffected and the salt rinses away in plain water, leaving a blue 'negative' image.
Atkins used Talbot's "photogenic drawing" method, arranging her specimens on sheets of glass for easier handling for repeat exposures, and adopted Herschel's blueprinting process, to generate the multiple copies of specimen plates comprising Photographs of British Algae.
I've posted only a handful of the 200-plus images Anna Atkins produced. You can browse the NYPL site to see them all.
Anna Atkins at 62 years of age in 1861.