Biography of Louis Daguerre, Inventor of Daguerreotype Photography

On August 19, 1839, the details of Louis Daguerre's firstst practical photographic process were released in Paris. An excerpt from the article:

"Partnership With Joseph Niépce
Daguerre regularly used a camera obscura as an aid to painting in perspective, which led him to think about ways to keep the image still. In 1826 he discovered the work of Joseph Niépce, who was working on a technique for stabilizing images captured with the camera obscura.

In 1832, Daguerre and Niépce used a photosensitive agent based on lavender oil. The process was successful: they were able to obtain stable images in under eight hours. The process was called Physautotype.

Daguerreotype
After Niépce's death, Daguerre continued his experiments with the goal of developing a more convenient and effective method of photography. A fortunate accident resulted in his discovery that mercury vapor from a broken thermometer could speed the development of a latent image from eight hours to just 30 minutes.

Although Louis Daguerre was rumored to be camera shy, he sat for this daguerreotype portrait around 1844. The Metropolitan Museum of Art, Gilman Collection, Gift of The Howard Gilman Foundation, 2005 / public domain
Daguerre introduced the daguerreotype process to the public on August 19, 1839, at a meeting of the French Academy of Sciences in Paris. Later that year, Daguerre and Niépce's son sold the rights for the daguerreotype to the French government and published a booklet describing the process.

The Daguerreotype Process, Camera and Plates
The daguerreotype is a direct-positive process, creating a highly detailed image on a sheet of copper plated with a thin coat of silver without the use of a negative. The process required great care. The silver-plated copper plate had to first be cleaned and polished until the surface looked like a mirror. Next, the plate was sensitized in a closed box over iodine until it took on a yellow-rose appearance. The plate, held in a lightproof holder, was then transferred to the camera. After exposure to light, the plate was developed over hot mercury until an image appeared. To fix the image, the plate was immersed in a solution of sodium thiosulfate or salt and then toned with gold chloride.

Exposure times for the earliest daguerreotypes ranged from 3-15 minutes, making the process nearly impractical for portraiture. Modifications to the sensitization process, coupled with the improvement of photographic lenses, soon reduced the exposure time to less than a minute.

Although daguerreotypes are unique images, they could be copied by re-daguerreotyping the original. Copies were also produced by lithography or engraving. Portraits based upon daguerreotypes appeared in popular periodicals and in books. James Gordon Bennett, the editor of the New York Herald, posed for his daguerreotype at Brady's studio. An engraving based on this daguerreotype later appeared in the Democratic Review."