A Manual Of Photography

MODIFIED PROCESSES. 225 found that Mr. Cundell’s process of manipulation is almost as good as any that can be adopted: and that gentleman certainly merits the thanks of the patentee, and of all photographic artists. Many modifications of Mr. Talbot’s mode of manipulating have been introduced with very variable advantages. I have, however, found that nearly every variety of paper requires some peculiar method to excite it to its maximum degree of sensi- bility. A few of the published methods may be noticed, as under different circumstances they may prove useful. Mr. Bobert Bingham, who has operated with such success, adopts the following process:— Apply to the paper a solution of nitrate of silver, containing 100 grains of that salt to 1 ounce of distilled water. When nearly, but not quite dry, dip it into a solution of iodide of potassium, of the strength of 25 grains of the salt to 1 ounce of distilled water, drain it, wash it, and then allow it to dry. Now brush it over with aceto-nitrate of silver, made by dissolving 50 grains of nitrate of silver in one ounce of distilled water, to which is added one-sixth its volume of strong acetic acid. Dry it with bibulous paper, and it is now ready for receiving the image. When the impression has been received, it must be washed with a saturated solution of gallic acid, and exposed to a steam heat, a jet of steam from the spout of a tea-kettle, or any convenient vessel. The image will be gradually brought out, and may be fixed with hyposulphite of soda. It will be observed that in this process the solutions of nitrate of silver and of gallic acid are not mixed before application to the paper, as in Mr. Talbot’s process. Mr. Channing, of Boston, very much simplified the calotype process. He directs that the paper should be first washed over with 60 grains of crystallized nitrate of silver, dissolved in 1 ounce of distilled water, and when dry, with a solution of ten grains of the iodide of potassium in one ounce of water: it is then to be washed with water, and dried between folds of blotting paper : the sensibility of the paper is said, and correctly, to be much improved by combining a little chloride of sodium with the iodide of potassium: 5 grains of tire latter salt, and rather less than this of the former, in an ounce of water, may be employed advantageously. To use this paper of Mr. Channing’s, where time is an object, it is necessary to wash it, immediately before it is placed in the camera obscura, with a weak solution of nitrate of silver, to which a drop or two only of gallic acid has been added. The picture is subsequently developed by the gallo-nitrate of silver, as already described. Q