The Hidden Architect of Photography explores the overlooked yet essential contributions of Sir John Herschel, whose scientific discoveries and intellectual insights laid the foundation for modern photography. Through this series, we reveal how Herschel’s innovations — from chemical breakthroughs to the very language of photography — shaped a new medium and revolutionized how we capture and interpret the world. Join me in uncovering the story behind the hidden architect who helped bring photography out of the shadows.

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The Hidden Architect of Photography – Sir John Herschel and the Discovery of “Hypo”

In the pantheon of early photography, names like Louis Daguerre and William Henry Fox Talbot loom large. Yet behind the scenes, the English polymath Sir John Frederick William Herschel played a pivotal role in overcoming one of the new medium’s most vexing problems: the lack of a reliable method to make photographs permanent.

This article – the second in a series titled “The Hidden Architect of Photography” – highlights Herschel’s crucial discovery and application of sodium thiosulfate (then known as hyposulphite of soda or simply “hypo”) as a photographic fixer. We will explore how Herschel identified hypo’s fixing properties, how and when he applied it to early photographic experiments, and how this breakthrough solved a major technical limitation in the nascent art of photography. Furthermore, we examine the broader significance of Herschel’s discovery: its impact on the permanence and reproducibility of photographs, its adoption by contemporaries such as Talbot and Daguerre, and its role in transforming photography from a scientific curiosity into a practical medium.

Herschel’s Early Discovery of “Hypo” (1819)

Herschel’s involvement with photographic chemistry began well before the public announcement of photography in 1839. As early as 1819, during chemical experiments unrelated to picture-making, Herschel observed a remarkable property of a substance called hyposulphite of soda. He found that this “hypo” solution could dissolve silver salts – in particular, silver chloride – with striking effectiveness, “as readily as water dissolved sugar”. This discovery was noted by Herschel in the context of pure chemistry, decades prior to the invention of practical photographic processes. Crucially, Herschel did not invent hypo (the compound was first prepared by others around 1799), but he was among the first to study its effects on silver compounds. In 1819, he recognized that a solution of hyposulphite of soda could “wash out” silver halides completely – a fact that would later prove invaluable.

Herschel’s early insight lay largely dormant for twenty years, as there was not yet a practical use for it in image-making. However, this deep well of chemical knowledge positioned Herschel uniquely: when photography’s first inventors eventually grappled with fixing images, Herschel already held the key. His scientific background (astronomy, chemistry, optics) and meticulous experimentation meant that he understood the chemical interactions at play. Thus, Herschel was poised to bridge the gap between theoretical chemistry and practical photography when the opportunity arose.

The Problem of Fixing Early Photographs

Prior to 1839, a major technical obstacle stood in the way of making photography truly viable: there was no known method to “fix” a photograph – that is, to prevent the continued darkening of the light-sensitive material after exposure. Early experimenters could capture temporary images, but these images were fleeting. In the 1790s, Thomas Wedgwood and Sir Humphry Davy, for example, created silhouettes on paper or leather coated with silver nitrate, but no sooner had they exposed their creations to light than the images began to darken and fade. Wedgwood lamented that he could not find a way to stop the “continuing action of light” on his pictures. As a result, those first proto-photographs had to be kept in darkness and were essentially ephemeral – a frustration that discouraged further development for decades.

By the 1830s, Henry Fox Talbot was independently experimenting with what he called “photogenic drawings” (photographic images on sensitized paper). Talbot’s early methods involved coating paper with silver chloride, which would darken upon exposure to sunlight to yield a negative silhouette of the subject. He too confronted the fixing problem: unless the excess silver chloride was removed or neutralized, the entire paper would eventually darken. Talbot tried a number of stopgap solutions. In 1834 he treated his sensitized paper with potassium iodide after exposure, which converted the remaining silver chloride to a more inert form of silver iodide. This was a partial fix – the image was somewhat stabilized, but not fully permanent. Talbot next discovered that washing the paper in a strong solution of common salt (sodium chloride) helped further; by the “glorious summer” of 1835 he realized that salt could render the excess silver chloride only minimally sensitive to light. Even in early 1839, just before the public reveal of photography, Talbot experimented with potassium bromide to convert leftover silver chloride to relatively insensitive silver bromide. Each of these methods – iodide, salt, bromide – could stabilize an image to a degree by chemically altering the unused silver halides, but none could completely remove those light-sensitive compounds from the paper. The photographs remained at risk of gradual darkening if subjected to sufficient light.

In summary, the lack of a true fixing agent was the single biggest technical limitation of early photography. Without a fixative, a photograph could not be reliably preserved or displayed. This limitation kept early photographic experiments in the realm of the tentative and experimental. The challenge was clear: inventors needed a way to halt the action of light on the remaining silver salts in a photographic image, ensuring that what was once visible would not eventually turn completely black. It was this challenge that Sir John Herschel was uniquely equipped to solve.

1839: Herschel Applies Hypo to the First Photographs

The year 1839 is famously known as the “dawn of photography” – it was in January of that year that Louis Daguerre’s photographic process was announced in Paris, and shortly thereafter, Talbot rushed to disclose his own work on paper photography in England. Herschel, although not initially part of the race to invent photography, was electrified by the news. On January 22, 1839, Herschel received a letter (from a friend who wrote to Herschel’s wife) describing Daguerre’s breakthrough with “light pictures”. Almost immediately, the scientifically curious Herschel began his own experiments. Drawing on his 1819 discovery, Herschel realized that the hyposulphite of soda in his laboratory might hold the answer to Daguerre’s and Talbot’s fixing problem. Indeed, within days Herschel was able to produce photographs and solve the persistent fixing issue using hypo.

Historical correspondence confirms this rapid development. On February 1, 1839, William Henry Fox Talbot – who by then knew Herschel well – visited Herschel at his home in Slough. During this visit, Herschel shared with Talbot the critical discovery: a bath of hyposulphite of soda could dissolve the unexposed silver halide in a photograph, effectively clearing away the light-sensitive material and leaving the image intact. In other words, Herschel had identified the first true fixer. Talbot, who had been using his weaker bromide and salt fixes, now stood on the cusp of a far more effective solution provided by his friend. By February 12, 1839, Herschel was writing to Talbot about this process, describing how the unwanted silver salts could be “washed out” completely – an elegant solution Talbot had not yet employed. This private correspondence and exchange of ideas highlight Herschel’s role as a scientific mentor in the background of Talbot’s work.

Herschel did not keep his findings to himself. Ever the scholar, he prepared a formal communication for the Royal Society. On March 14, 1839, Herschel presented his paper “On the Art of Photography; or the Application of the Chemical Rays of Light to the Purpose of Pictorial Representation.” This seminal paper (often just called the “Note on the Art of Photography”) was one of the first scientific publications on the new medium. In it, Herschel described various photographic experiments he had carried out and crucially mentioned the use of hyposulphite as a fixing agent. He demonstrated that images could be made permanent “and completely resistant to further reaction with light” by treating the prepared photograph with sodium hyposulphite. That is, once washed in the hypo solution, the photograph’s remaining silver salts were gone, and the image would no longer alter upon exposure to daylight. Herschel’s Royal Society paper also introduced much of the lexicon of photography – he is credited with coining the very term “photography” (from Greek roots meaning “light writing”), as well as the words “positive,” “negative,” and “emulsion,” to describe aspects of the process. This linguistic contribution underlined how thoroughly Herschel grasped the principles of the new art; he was helping to define photography conceptually at the same time as he advanced it technically.

In the span of a few weeks in early 1839, Herschel had transitioned from an intrigued outsider to a central figure in photographic science. By applying hypo as a fixer, he supplied the solution to what Daguerre and Talbot had identified as a critical obstacle. Herschel’s laboratory in Slough became a hub of photographic knowledge – Talbot continued to correspond and exchange findings with him – and Herschel’s Royal Society lecture spread the word quickly through the scientific community that the “hypo” fix was available to all. Herschel’s discovery thus rapidly entered the toolkit of photography’s inventors.

“Hypo” and the Achievement of Permanence

Herschel’s use of sodium thiosulfate as a fixer proved to be revolutionary. By removing the unexposed silver halide crystals from a photographic surface, hypo solved the problem of image permanence in a decisive way. Earlier “fixing” methods had only transformed the remaining silver salts into a slightly more stable form (e.g. silver iodide or silver bromide), but those inert salts still lingered in the paper or plate. Under prolonged light exposure, even those could eventually cause discoloration or fading. In contrast, a wash in hyposulfite of soda completely dissolved the residual silver compounds, allowing them to be washed out and discarded. After a thorough hypo fixing and water rinse, what remained on the photograph was only the reduced metallic silver that formed the image – a substance largely insensitive to light. The result was a genuinely permanent photograph.

Contemporaries immediately recognized how critical this breakthrough was. One scientific account of 1839 noted that Herschel’s hyposulphite fixer rendered the photographic image “completely resistant” to further action of light. For the first time, it became possible to preserve a photographic image indefinitely and to view it in normal illumination without fear of it vanishing. Herschel himself demonstrated this by fixing his experimental photographs. (In fact, one of Herschel’s photographs from 1839 – a photograph of his father’s 40-foot telescope, taken on a glass plate – still exists today, albeit faded, testament to the early attempts at permanence.)

The importance of hypo in achieving true photographic permanence can hardly be overstated. It liberated photography from darkness. Whereas Wedgwood’s fragile creations had to be kept in a portfolio, and even Talbot’s early salt-fixed “photogenic drawings” were best stored away from sunlight, a hypo-fixed photograph could be framed and hung on a wall or used in a book without quickly degrading. This meant photographs could serve as lasting documents and artworks rather than momentary curiosities. As historian Larry J. Schaaf explains, Herschel’s “hypo” essentially became “the fixer essential to making silver-based photographs permanent.” It finally provided a reliable answer to the medium’s fundamental archival question: will the image endure?

Furthermore, Herschel’s fixer had implications for reproducibility. In Talbot’s negative-positive process, for example, one could make multiple positive prints from a single paper negative. But those negatives and prints needed to be stable over time to produce and keep multiple copies. With hypo, a paper negative could be fixed and preserved, allowing Talbot (or any photographer) to return days or weeks later and still use it to print additional copies. Likewise, positive prints fixed in hypo could be made in batches and sold or distributed, with confidence that each copy was permanent. Photographic reproducibility on any meaningful scale was thus predicated on having a proper fixative. Herschel’s contribution directly enabled Talbot’s vision of photography as a means of mass duplication of images. In short, hypo gave photography both its longevity and its replicability, two qualities essential for the medium’s practical adoption in science, art, commerce, and daily life.

Adoption by Talbot and Daguerre

Once Herschel introduced the hypo fixer in 1839, it quickly spread among the inventors of photography – albeit with some differences in enthusiasm. Louis Daguerre, whose daguerreotype process was announced that year, was among the first to embrace the new fixative. Daguerre’s original method for fixing his silver-coated plates involved a hot saturated salt water bath, which could stabilize the image to an extent. However, news of Herschel’s hyposulphite solution reached Daguerre soon after its discovery, and it proved to be a more efficient alternative. In the published manual Historique et Description des procédés du Daguerréotype (1839), Daguerre himself mentions that any remaining iodine (from the light-sensitive silver iodide on the plate) could be “completely removed by means of a rinse in sodium hyposulphite or in sea salt”. This statement – coming from Daguerre’s official instructions – confirms that by the time the daguerreotype process was made public, Herschel’s fixer had been integrated into it. The hypo wash not only improved the permanence of the daguerreotype image but also tended to produce a cleaner, less discolored plate (Daguerre noted that the hypo eliminated certain reddish tones that the salt method sometimes left). Thus, thanks to Herschel, Daguerre’s metal photographs could be made as enduring as possible, accelerating the spread of daguerreotype portrait studios worldwide in the 1840s.

William Henry Fox Talbot, on the other hand, showed a bit more caution in switching to hypo. Talbot greatly admired Herschel – indeed he had solicited Herschel’s advice early on – but Talbot had already invested effort into his own partial fixing agents. When Herschel alerted Talbot in February 1839 about the power of hyposulphite, Talbot did begin using it in some experiments, yet he did not immediately make it his standard fixer. Throughout 1839 and 1840, Talbot often continued to use potassium bromide or strong salt solutions for his paper negatives. One reason may have been that these different fixes imparted different hues to the paper (for example, salt could leave a lavender tint, iodide a yellow stain, whereas hypo produced a neutral tone). Talbot might have been balancing aesthetic considerations or simply relying on familiar techniques while he perfected other aspects of his process (such as developing the latent image with gallic acid, which he discovered in 1840). By 1841, when Talbot introduced the calotype (an improved paper negative process which he patented), he was still recommending a bromide fixer in his formula. However, experience soon showed the superiority of hypo. By 1842, Talbot had largely adopted Herschel’s hypo for fixing the final prints made from calotype negatives. Over time, even Talbot’s negatives were fixed with hypo to ensure maximum stability, especially as others refined the paper process. In the end, Talbot fully acknowledged the importance of Herschel’s contribution – he knew that without a good fixer, his beautiful “Talbotypes” would not stand the test of time.

Outside of Daguerre and Talbot, virtually all early photographers who learned of hypo incorporated it. The knowledge spread through scientific correspondence and publications. For instance, the eminent scientist Sir John Herschel himself was in communication with other pioneers and scientists across Europe. We see references to hyposulphite in photographic journals and letters almost immediately after 1839, often citing Herschel’s experiments. The universal adoption of hypo was evident: by the 1840s, whether one was making a daguerreotype on silvered copper, a paper calotype, or later a glass plate negative, the final fixing bath was invariably a solution of sodium thiosulfate. Herschel had given the medium one of its most enduring chemical tools – one that remains in use even in modern photographic film development.

It is telling that Herschel’s name became practically synonymous with the fixer in those early years. A later commentary noted that mention of Herschel inevitably “evoke[s] a discussion of hypo”, so intertwined were the man and the chemical in the minds of photographers. While others gained fame for capturing images, Herschel was revered as the one who made those images permanent.

From Experiment to Practical Medium

Herschel’s introduction of the hypo fixer in 1839 was a turning point that allowed photography to evolve from a fragile experiment into a robust, practical medium. With permanence assured, the implications were far-reaching. Photographers could now confidently exhibit their work, sell photographs, and use the camera to document the world, knowing that the results would last. In the early 1840s, this confidence gave rise to the first photographic studios and publications. For example, by 1844 Talbot felt secure enough in the durability of his calotype prints to publish The Pencil of Nature, the first commercial photographically illustrated book – a project unthinkable without a reliable fixing method to preserve the plates during printing and handling. Similarly, scientific and artistic uses of photography blossomed once images could be kept without fading. Astronomers, archaeologists, and tourists alike began to take and keep photographs as records. This leap from the laboratory to society at large was powered in no small part by Herschel’s hypo. The major technical limitation of earlier processes – their impermanence – had been overcome, enabling photography’s transition into a practical tool for communication and memory.

Furthermore, the hypo fixer underpinned the reproducibility and spread of photography. A permanent negative could yield dozens of prints; a well-fixed print could be shipped across oceans. The medium’s influence expanded dramatically in the 19th century precisely because photographs could be duplicated and disseminated without immediate deterioration. One might say that Herschel’s contribution “fixed” not only the images themselves but also photography’s place in history. Without stable photographs, the world’s first snapshots of people, places, and events in the 19th century might not have survived for us to admire today. Thanks to Herschel, many of those 1839–1840 photographs are indeed still extant, their delicate images having outlived the era in which they were made – a true testament to the efficacy of his discovery.

Sir John Herschel’s work exemplifies how an often unsung figure can profoundly shape a field. He did not seek to patent or profit from his fixer; instead, he openly shared it for the benefit of the nascent art. Herschel himself continued to innovate in photography, inventing the cyanotype process in 1842 and contributing in other ways, but it is the simple act of applying “hypo” to a light-exposed sheet of paper that stands as his most celebrated contribution. It solved the key problem that had stymied photography’s pioneers and thereby unlocked the door to all that followed. Modern photographic historians rightly recognize Herschel as “a photographic genius who deserves his rightful place alongside the early pioneers of the medium.” Daguerre and Talbot may have shown how to capture images, but Herschel ensured those images would endure. In this sense, Herschel is truly a “hidden architect” of photography – an indispensable figure who quietly laid the foundations (in chemistry and language) upon which the edifice of photography was built. His discovery of the hypo fixer remains one of the cornerstones of photographic science, demonstrating how a single chemical insight can change the course of technological history.

References (Bibliography)

• Herschel, J. F. W. (1839). “Note on the Art of Photography, or the Application of the Chemical Rays of Light to the Purpose of Pictorial Representation.” Proceedings of the Royal Society of London, 4: 131–133. (Herschel’s communication to the Royal Society introducing the term photography and discussing the fixing of images with hyposulphite.)
• Schaaf, Larry J. (2016). “To fix or not to fix? – Sir John Herschel’s question.” Talbot Correspondence Project (Blog, Bodleian Libraries). (Detailed historical discussion of Herschel’s 1819 experiments with “hypo” and its adoption by Talbot and Daguerre.)
• International Photography Hall of Fame (n.d.). “Sir John Herschel.” (Biography entry noting Herschel’s January 1839 experiments and his solution to the fixing problem based on his 1819 research.)
• FamousScientists.org (n.d.). “John Herschel.” (Article noting Herschel’s discovery that sodium thiosulfate makes images permanent by dissolving silver halides.)
• Daguerre, Louis (1839). Historique et description des procédés du Daguerréotype et du Diorama. Paris: Alphonse Giroux et Cie. (Daguerre’s manual in which he mentions removing residual iodine with hyposulfite of soda or salt, indicating early adoption of Herschel’s fixer.)
• Blog.sciencemuseum.org.uk – Alison Boyle (2010). “A Glass Act.” (Describes Herschel’s first photograph on glass, taken 9 September 1839, and its current condition – evidence of early fixing efforts.)
• Wilson, Dale (2021). “Herschel – An Unsung Pioneer.” Antique Pictureology (blog). (Highlights Herschel’s role in coining “photography” and emphasizes his status as a key figure in early photography.)
• Schaaf, Larry J. (2024). The Cambridge Companion to John Herschel – Ch. 7 “Photology, photography, and actino-chemistry: the photographic work of John Herschel” (edited by S. Case & L. Verburgt). Cambridge Univ. Press. (Not directly quoted above, but a scholarly overview of Herschel’s contributions.)
• Additional correspondence: Herschel to W. H. F. Talbot, February 1839, Royal Society Archives (HS 25/5/12). (Herschel’s letter reporting the successful fixing of photographs by washing away unexposed salts – corroborating the timeline in which Herschel shared the hypo fixer with Talbot.)

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