In 1839, an artist opened a chemical cabinet: And a hidden image helped launch photograph

When thinking about the invention of photography, one usually assumes that some moment occurred when someone took a photograph on the very first try. The reality, however, was not as spectacular as expected. In 1839, French artist and inventor Louis Daguerre developed a photographic method that was based on an invisible process. Having exposed a silver plate to the light source in a camera obscura, it was unlikely that any image would appear on it. There were images, but those remained invisible. However, a certain second chemical reaction made the image visible again. According to Daguerre, an important step towards discovering this process occurred when the exposed plate was placed in a cabinet filled with various chemicals. Returning home after such an experiment, one could see that a picture had been produced on the plate, which led to the idea of developing it with mercury vapor.

This invention revolutionized the field of photography, making it a viable practice. Photography used to require a long exposure, which, however, produced visible images instantly. Now it was possible to produce images by first capturing them invisibly and later developing them chemically.

The photograph existed before anyone could see it

The notion of latent image creation was another revolutionary element associated with the daguerreotype, since, according to Cornell University's "Dawn's Early Light" photographic process archive, the first phase of the process was to create an invisible image by exposing a light-sensitive silver-plated copper plate to light. At this point, the image already existed; however, its visibility needed additional treatment. Although this might seem like a simple technical nuance, it marked an important paradigm change since traditional image-making technologies required the existence of the object to be visualized. In the case of the daguerreotype, the camera recorded the necessary data, while the chemistry made the image visible.


As explained by Cornell University's "Dawn's Early Light" photographic process archive, the process included several stages: iodization, exposure, developing with mercury vapor, fixing, and washing. Since the technology was sufficiently consistent to be used repeatedly, it enabled the development of a technique that others could learn and replicate.

Mercury vapor turned a hidden pattern into a photograph

The important breakthrough in Daguerre's work was understanding how to magnify the faint pattern formed by exposure. Nowadays, scientists can describe the processes at work. One such study, published in the Proceedings of the National Academy of Sciences, states that silver-mercury compounds form as a result of exposure, thereby amplifying the image and making the previously undetectable pattern apparent. To put it simply, the camera records the information, while mercury development enables its visualization.

According to The Smithsonian Institution's Lemelson Center, the development of mercury was crucial to creating a practical daguerreotype process; otherwise, it would have been unfeasible. Mercury development was important because it helped transform a weak photographic image into something more tangible, and it could be considered the point at which photography began proving useful. With the development of mercury, artists were no longer necessary for image creation. Instead, all the needed components of image formation were present: light and metal.

The breakthrough changed how people trusted images

The year 1839 is considered the dawn of photography inasmuch as it marked the time when Daguerre’s invention was made public knowledge and could therefore be practiced by anybody else. According to the conservation review in Heritage Science, daguerreotypes emerged from obscurity in 1839, using mercury vapor in their development prior to chemical fixation. More significantly, the technique could be studied, copied, and enhanced, which occurred promptly enough; the refinement in the process, including bromine sensitivity and gold chloride coating, according to Cornell’s history guide, greatly improved the resulting image and shortened the exposure time. The value of Daguerre's invention lay not in his having discovered the ideal process for taking photographs. It lay in having invented a feasible process that future generations of inventors and photographers could work with. Prior to the advent of photography, most visual depictions were done by artists using pen and paint and whatever medium of expression they chose. With the daguerreotype, people were getting an image produced by nothing but light.

Not without its faults, the process was fragile, costly, and hard to replicate, but it revolutionized the way people thought about the possibilities of imagery. One could now capture a person’s face, a vista, or a historic moment in a way no other method before it could. In retrospect, it would seem the discovery was surprisingly modest. The light-sensitive plate had been lying unseen in the dark cabinet all along. Chemicals made it possible to uncover something that had always been there but had not yet been seen. What was illustrated here was one of the most powerful concepts in the history of photography: an image need not be seen at the time of its creation to exist. Light can inscribe information onto a surface, and chemicals make it visible again. The latent image remained concealed for only a brief time before Daguerre realized how to uncover it.