CAL'OTYPE (Gk. saX6s, kalos, beautiful, renros, typos, impression). A name applied to one of the earliest processes for producing photo graphic prints, as well as to the prints them selves. The process was invented by Henry Fox Talbot in 1840. It consists of the following oper ations. A sheet of good plain paper with a smooth surface and a close and even texture, is washed by means of a soft brush with a solu tion of 100 grains of crystallized silver nitrate in li ounces of distilled water. The paper is allowed to dry in a dark room and is then dipped into a solution of potassium iodide made by dis solving 500 grains of that salt in a pint of water. After a few minutes it is removed and then dipped into water and dried. This `iodized paper' is exceedingly sensitive to light, and may be kept for some time if it is carefully protected front sunlight. When required for use, a sheet of it is washed in a mixture which IMr. Talbot called gallo-nitrate of silver. The mixture is obtained by adding a saturated solution of gallie acid to an equal volume of a solution of 100 grains of crystallized silver nitrate in 2 ounces of distilled water, to which one-sixth of its volume of strong acetic acid had been added. After the iodized
paper has been washed over with this solution it is dipped into water and then cautiously dried with blotting-paper. An exposure of less than a second in diffused daylight is sufficient to obtain an impression. In order to develop the impres sion the paper is again washed with gallo-nitrate of silver and dried near a fire, the exposed por tions becoming brown, while the covered portions retain their original color. The picture is then fixed by consecutively washing it in clean water, drying, washing in a solution of potassium bro mide (10(1 grains in S ounces of water), washing in water to remove any surplus iodide solution, and finally drying.
The ealotype process has been superseded by other processes, and is at present hardly ever used. See PHOTOGRAPHY.