Information AboutCalotype |
| CATEGORIES ABOUT CALOTYPE | |
| photographic processes | |
| history of photography | |
| british photography | |
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It may be briefly described as the application of silver iodide to a paper support. Carefully selected paper was brushed over with a Solution of Silver Nitrate (100 Grains to a Fluid Ounce of distilled Water , or 5 g/L), and dried by the fire. It was then dipped into a solution of potassium iodide (500 grains being dissolved in an imperial Pint of water, or 57 g/L ), where it was allowed to stay two or three minutes until silver iodide was formed. In this state the iodide is scarcely sensitive to Light , but is sensitized by brushing "gallo-nitrate of silver" over the surface to which the silver nitrate had been first applied. This "gallonitrate" is merely a mixture, consisting of 100 grains of silver nitrate dissolved in 2 fluid ounces of water (114 g/L), to which is added one-sixth of its volume of Acetic Acid , and immediately before applying to the paper an equal bulk of a saturated solution of Gallic Acid in water. The prepared surface is then ready for Exposure in the Camera , and, after a short insolation, develops itself in the dark, or the development may be hastened by a fresh application of the "gallo-nitrate of silver." The picture is then fixed by washing it in clean water and drying slightly in blotting paper, after which it is treated with a solution of Potassium Bromide , and again washed and dried. Here there is no mention made of hyposulphite of soda as a fixing agent, that having been first used by John Herschel in February 1840 . This process was the first to use a Negative image that can be reused to produce several positive prints. Its primary weakness was in the reliance on a paper surface, as the fiber patterns and other imperfections were inevitably reproduced in prints. One available solution was to use a Glass plate negative, but first it was necessary to find a way to bind the chemicals to the glass. This was accomplished in the early 1850s with the development of Albumen Print s and the Collodion Process , after which the calotype became obsolete. |
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