The daguerreotype was the first photographic process made public, in 1839: a one-of-a-kind image formed on a silvered copper plate, sensitised with iodine vapour and then developed with mercury vapour. It produces no negative, which is why the paper pinhole camera descends from Talbot's calotype instead, its great rival of the 1840s.
This page explains how the daguerreotype worked, without suggesting you try it, because its mercury chemistry has no place at home. Like all photography of the period, it was born in a camera obscura, a closed box in which light forms an image, the very principle of the pinhole camera.
A silver plate polished like a mirror
It all starts with a sheet of copper coated with a thin layer of silver, cleaned and then polished to a mirror finish, as the Historic New Orleans Collection describes. The image forms on this metal, not on paper.
The plate is then shut in a light-tight box, above iodine. The vapour reacts with the silver and forms silver iodide, which is sensitive to light, until the surface turns yellow. Bromine vapour was later added to increase this sensitivity.
The exposure, then development with mercury
The sensitised plate goes straight into the camera, which is fitted with a lens. The first exposures lasted from three to fifteen minutes. With better lenses and the addition of bromine, a portrait needed only about one minute.
When it comes out of the camera, nothing is visible: the image is latent. It is developed by placing the plate face down above heated mercury, until the image appears. The mercury forms an amalgam with the silver and picks out the highlights in a milky white.
The image then has to be fixed so that it no longer changes. A solution of table salt was used at first, then hyposulphite of soda, the famous “hypo”, took over. A bath of gold chloride then intensified the image before a rinse in distilled water.
This hypo had been proposed by the astronomer John Herschel, the very man who invented cyanotype in 1842. It is still this compound, sodium thiosulphate, that fixes black and white prints today.
A one-of-a-kind, reversed image
The daguerreotype is a direct positive. No negative is made, and each plate remains a one-off object that cannot be printed in several copies.
The image is also reversed left to right, as in a mirror. You barely notice it on a portrait, but a shop sign or an inscription in a street view reads backwards.
Its mirror polish gives it one last strange feature: depending on the angle from which you look at it, the plate appears positive or negative. Being fragile, it was protected by glass and kept in a case.
Marie-Charles-Isidore Choiselat and Stanislas Ratel, Parade on the Pont-Royal, daguerreotype, 1 May 1844. The Metropolitan Museum of Art, New York. Public domain.
Niépce and Daguerre: a decisive partnership
Louis Daguerre, a scene painter known for his Diorama, a Parisian spectacle, was trying from the mid-1820s to capture the images of the camera obscura. In 1829, he went into partnership with Nicéphore Niépce, who was working on the same problem and had already obtained lasting images.
Niépce died in 1833 before the two partners had found a reliable process, and Daguerre carried on alone. On 7 January 1839, his images were shown to the Académie des Sciences. On 19 August 1839, François Arago presented the process at a joint meeting of the Académie des Sciences and the Académie des Beaux-Arts.
The French state granted Daguerre a life pension in exchange for the rights to his process, which entered the public domain, whereas Talbot would patent his calotype in 1841. It was a turning point in the history of the fixed image.
Daguerreotype or calotype
Born two years apart, the daguerreotype made public in 1839 and the calotype patented in 1841 produce two opposite objects.
- Support: a silvered copper plate for the daguerreotype, a sheet of paper for the calotype.
- Result: a one-of-a-kind direct positive on one side, a negative from which positives are contact printed on the other.
- Development: with mercury vapour for one, with gallo-nitrate of silver for the other.
- Look: very sharp detail and a mirror effect versus a softer image, marked by the paper fibre.
The daguerreotype won people over at first with its precision. But it is the principle of the negative, from which you can print as many copies as you like, that prevailed throughout analogue photography.
Why the pinhole camera descends from the calotype
A pinhole camera loaded with photographic paper produces a negative on paper. It is developed in a developer, fixed, then turned into a positive by scanning or by contact printing on a second sheet.
This is exactly the logic of Talbot's calotype and its paper negative, and not that of the daguerreotype. The modern pinhole camera therefore inherits paper and contact printing, not the silver plate.
One nuance is needed, however. The daguerreotype was made in a camera fitted with a lens. The pinhole camera in the strict sense, with no lens at all, only became a photographic choice a little later in the 19th century.
Why it is not something to recreate at home
Developing a daguerreotype relies on heated mercury. And mercury is toxic: human exposure occurs mainly through inhaling its vapour (in French), the WHO points out, and its compounds can cause neurological disorders.
That is why this page sticks to understanding the process, and daguerreotypes are best admired in museums. Unlike the daguerreotype, a paper negative can be made at home, with a pinhole camera loaded with paper such as the Sténoflex mini-lab, which also provides the developer and the fixer.
Header image: portrait of Louis Daguerre, daguerreotype by an unknown author, c. 1844. The Metropolitan Museum of Art, New York. Public domain.
Éric Marais — Photographer, author of two books on pinhole photography (published by Pearson) and creator of the Sténoflex. Since the very beginning, he has run introductory workshops in pinhole photography and analogue developing.