A paper negative is a negative image obtained on a light-sensitized sheet of paper exposed in a view camera. Invented simultaneously with the Daguerreotype, it brought photography into its modern era by introducing the "negative-positive" process for the first time, making it possible to produce more than one print from the same negative image. The term "paper negative" covers a variety of techniques which can be difficult to differentiate. All of them are variants of the calotype (or talbotype) visually process patented by William Henry Fox Talbot in 1841 after his discovery of the photogenic drawing.
Calotypes are produced as follows: a high-quality sheet of paper is coated with a silver nitrate solution using a paintbrush, then dried. Next, it is dipped in a potassium iodide solution for several minutes, for an initial round of sensitization by forming silver iodide. After being dried again, this time in the dark, it is treated with "gallo-nitrate of silver," a solution consisting of silver nitrate, gallic acid and acetic acid. Once it is rinsed, the sheet, wet or dry, must be quickly placed in the camera to capture the image. Exposure produces a latent image, barely visible to the naked eye, which is revealed by development in a solution of gallo-nitrate of silver. The developed image is then stabilized in a potassium bromide bath--although this was gradually replaced in the second half of the 1840s with sodium thiosulfate, called hyposulfite of soda at the time. The resulting negative is usually coated with wax for more transparency. Until the 1850s, salted paper prints were made by contact with paper negatives in a printing-frame.
The paper negative processes were used in the 1840s and 1850s, first in England where it was invented, and then in France starting in the late 1840s. Commercial development of the calotype was hindered by its inventor's many patents, as well as the visual characteristics of the resulting image–brown or sepia tones, high contrast, and slightly blurry results. The many improvements made to the process in France, however, along with the expiration of the patents in 1852, made it a notable success, especially with enthusiasts and artists such as Charles Le Nègre, Henri Le Secq, Charles Marville and Gustave Le Gray in France. Those using calotypes formed photography circles and societies: the Calotype Society in England, a circle around Robert Adamson in Scotland, the Roman Photographic School (Caffè Greco group), and several other groups in France within the Manufacture de Sèvres and the Société Héliographique. The process, because of the long exposure time, was not totally suited to portraits, it was popular for outdoor and travel photography and still lifes.
Louis Désiré Blanquart-Évrard improved the wet paper negative process, enabling the calotype to take off in France starting in 1847, releasing the Talbot procedure from its patent and facilitating its adoption. The new approach reduced the amount of handling required to prepare the paper for exposure, shortened exposure times, and improved the resulting image. The Lille-based experimenter would go on to develop several other variants of paper negatives based on albumen, serum and whey.
In 1851, Gustave Le Gray perfected the Talbot procedure with his dry waxed paper process. This technique, which recommends waxing the paper before sensitizing it, extends the shelf life of prepared papers and gives greater transparency to produced negatives. However, it also lengthens the exposure time.
The paper negative process was gradually abandoned in the late 1850s in favor of glass plate negatives, which produce higher-quality images. Nonetheless, it made a comeback in the second half of the 1880s for industrial purposes: in 1884, the Eastman Dry Plate and Film Company (Eastman Kodak) began producing rolls of sensitized paper which it would develop, prefiguring the massive adoption of photography. Because the resulting images were only of mediocre quality, Kodak replaced the paper with a flexible nitrate-based film base starting in 1888.