Calotype
The calotype (of the Greek kalos , beautiful and typos , impression) is a photographic process invented by William Henry Fox Talbot and patented in 1841. It makes it possible to obtain a negative direct paper and thus the possibility of reproducing positive images by simple Tirage contact. The negative-positive process will become the base of the silver Photographie modern.
In 1844, Talbot published the first book illustrated by the Photographie, Pencil off Natural ( the Pencil of nature ). This work contained twenty-four calotypes except text.
In France, it is Louis Désiré Blanquart-Evrard which carried out with Lille the first impressions of photographs with this process.
Obtaining negative paper
To prepare the photosensitive support which is used for negative, one coats a sheet of paper with letters frozen of a nitrate solution of money. Once dries, one plunges it in an iodide solution of Potassium. It is formed money iodide then. The sheet can be then washed with water and dried to be stored safe from the Lumière.
To make a test, it is necessary to finish preparing the photosensitive support. The sheet of paper covered with money iodide is coated with a mixture of gallic acid and silver nitrate, that Talbot called “money gallo-nitrate”.
The sheet is used dry or wet in the darkroom. The exposure time varies few seconds at a few minutes, according to the lighting and the color of the subject photographed. After the exposure, the image is developed in money gallo-nitrate, fixed with soda a hot hyposulphite solution, then washed with water, dried and waxed.
Negative paper thus obtained is of color grisâtre or brown dark. The fibers of paper can give him a granulous appearance, which harms the quality of the final image, compared to that of the Daguerréotype.
Pulling of the positive one
The sheet of paper which will be used as support with the positive image is initially wet in a solution of cooking salt, then, after a short drying, coated with a silver nitrate solution. After drying, it can receive one second layer of silver nitrate, to increase its sensitivity.
Negative paper is applied to the positive support. The two sheets are maintained in contact by pressure in a frame, then exposed to the light, negative top, until the positive image is formed on the second sheet. This one is then fixed with soda hyposulphite, as for the negative one.
Talbot had initially employed potassium bromide like Fixateur, before adopting the soda hyposulphite, according to the technique which he had learned from Sir John Herschel. The soda hyposulphite, or sodium thiosulfate, has the property to dissolve money salts. This product is still used today as fixer in silver photography.
External bonds
- Association of Néocalotypistes Photographers, heading “the process calotype”. Foot-note bucket : the site does not seem updated any more, but there still existed at the 9/26/2005.
| Random links: | Garage sees | Greens of the Benign one | New Washington (Aklan) | Rue de la Montagne-Sainte-Geneviève | Large medal of the French song | Boston_est,_le_Massachusetts |