5.1.4: The Fix and Cyanotype

Sir John Herschel: Fixing the Image and Inventing the Blueprint

Sir John Frederick William Herschel (1792–1871), pronounced HUR-shel, occupies a pivotal place in the history of photography—not as an inventor of the camera or the photographic process itself, but as the scientific mind who stabilized, clarified, and expanded its potential. A polymath of the highest order, Herschel was a mathematician, astronomer, chemist, and philosopher. His intellectual range enabled him to contribute key technical solutions to early photography while also shaping the terminology and conceptual foundation of the new medium.

"Fixing" Photography: The Invention of Hypo

When William Henry Fox Talbot and Louis Daguerre introduced their photographic processes in 1839, a fundamental problem remained: the images were unstable. They darkened or disappeared with prolonged exposure to light. Herschel resolved this issue with a discovery that would permanently anchor photography’s practicality: the use of sodium thiosulfate (commonly known as hypo) as a fixing agent.

In a paper delivered to the Royal Society in March 1839, titled “On the Action of the Rays of the Solar Spectrum on Vegetable Colours, and on some New Photographic Processes,” Herschel demonstrated that hypo could dissolve the unexposed silver halides on a photographic surface while leaving the image intact[i]. This meant that photographic prints, once fixed, would not degrade with further light exposure. It was a breakthrough that Talbot and Daguerre quickly adopted, and it remains the basis for photographic fixing in silver-based processes to this day.

Naming the Medium

Herschel also shaped how we speak about photography. He coined many of the foundational terms we still use:

· “Photography” – from the Greek phōs (light) and graphē (drawing), meaning “drawing with light”[ii].

· “Positive” and “Negative” – describing the tonal relationships in image production.

· “Snapshot” – later adopted to describe quick, candid exposures.

These linguistic contributions helped codify photography as a distinct visual and scientific discipline at a time when its identity was still in flux.

The Cyanotype: A Democratic Process

Herschel’s most original photographic invention was the cyanotype process, which he introduced in 1842. Unlike Talbot’s silver-based calotypes, cyanotypes used iron salts rather than silver to create light-sensitive emulsions. The process involved coating paper with a solution of ferric ammonium citrate and potassium ferricyanide, then exposing it to sunlight under a negative or object. The result was a Prussian blue image, which could be fixed simply by rinsing it in water[iii].

Cyanotypes offered several key advantages:

• · Simplicity – the chemistry was safer and more affordable than silver processes.

• · Permanence – cyanotype images are remarkably stable and resistant to fading.

• · Accessibility – the process could be done without a darkroom, making it available to amateurs and scientists alike.

The most celebrated early use of cyanotype was by Anna Atkins, who in 1843 began publishing British Algae: Cyanotype Impressions—widely considered the first book illustrated with photographic images. Atkins used the process to create delicate contact prints of seaweed specimens, combining scientific accuracy with visual elegance[iv].

A New Visual Language

Herschel saw in cyanotypes not just a scientific curiosity, but a new method of visual communication. The process was widely adopted for practical applications, most famously in the “blueprint”—a term derived from the cyanotype's distinctive color. Architects and engineers embraced cyanotypes to copy technical drawings efficiently and inexpensively, a practice that continued into the 20th century.

As art historians like Larry Schaaf have noted, the cyanotype marked a democratization of photography. It allowed scientific, botanical, and artistic imagery to be produced without expensive materials or specialized equipment[i]. This placed Herschel’s contribution alongside those of Talbot and Daguerre in expanding photography’s reach and utility.

A Pathway to Permanence and Possibility

The innovations of Sir John Herschel provided the chemical and conceptual foundation that allowed photography to move from fragile curiosity to durable medium. His discovery that sodium thiosulfate could “fix” a photographic image made permanence possible, while his invention of the cyanotype process offered a safe, affordable, and reproducible alternative to silver-based methods. In doing so, Herschel not only stabilized photography—he democratized it.

It was within this democratized space that Anna Atkins found her voice. The cyanotype allowed her, a scientifically educated woman without institutional access, to publish one of the most groundbreaking photographic works of the 19th century. British Algae: Cyanotype Impressions married science and art, authorship and reproduction, method and beauty. It stands as a direct consequence of Herschel’s vision: that photography could serve as a universal visual language, accessible to those outside traditional artistic or academic circles.

Yet even amid these advances, the medium was still evolving. The daguerreotype, with its stunning clarity and detail, captivated early audiences—but its images were one of a kind, trapped in metal and unable to be copied. The calotype, developed by William Henry Fox Talbot, introduced the negative-positive process, enabling reproduction, but its paper negatives created images with a softer focus due to the texture of the fibers.

This trade-off—between the daguerreotype’s crisp precision and the calotype’s reproducibility—would soon find resolution in a new process: the collodion wet plate. Introduced in 1851 by Frederick Scott Archer, the collodion process combined the fine detail of the daguerreotype with the reproducibility of the calotype, while using a glass plate that provided a smooth surface for sharper images. It would quickly become the dominant photographic method for the remainder of the 19th century.

But the path to the collodion plate was paved by the chemical insights of Herschel, the vision of Talbot, the public drama of Daguerre, and the quiet elegance of Atkins. Each advanced the medium not only in technical terms but in expanding who could participate, what could be documented, and how photography could serve the needs of both science and society.

Photography was no longer the domain of the few. It had entered the world—and the world, in turn, would never be seen the same way again.