The History and Practice of the Art of Photography [38]
this way, a great number may frequently be made.
The calotype pictures when prepared as we have stated, possess a yellowish tint, which impedes the process of taking copies from them. In order to remedy this defect, Mr. Talbot has devised the following method. The calotype picture is plunged into a solution consisting of hyposulphite of soda dissolved in about ten times its weight of water, and heated nearly to the boiling point. The picture should remain in about ten minutes; it must then be removed, washed and dried. By this process the picture is rendered more transparent, and its lights become whiter. It is also rendered exceedingly permanent. After this process the picture may be waxed, and thus its transparency increased. This process is applicable to all photographic papers prepared with solutions of silver.
Having thus fully, and it is hoped clearly, considered the process, it may be necessary before dismissing the calotype from notice, to add one or two remarks from the observations and labors of some who have experimented in this art. Dr. Ryan in his lectures before the Royal Polytechnic Institution, has observed, that in the iodizing process the sensitiveness of the paper is materially injured by keeping it too long in the solution of iodide of potassium, owing to the newly formed iodide of silver being so exceedingly solvable in excess of iodide of potassium as in a few minutes to be completely removed. The paper should he dipped in the solution and instantly removed. There is another point, too, in the preparation of the iodized paper in which suggestions for a slight deviation from Mr. Talbot's plan have been made. In the first instance, it is recommended that the paper be brushed over with the iodide of potassium, instead of the nitrate of silver, transposing, in fact, the application of the first two solutions. The paper, having been brushed over with the iodide of potassium in solution, is washed in distilled water and dried. It is then brushed over with nitrate of silver, and after drying is dipped for, a moment in a fresh solution of iodide of potassium of only one-fourth the strength of the first, that is to say, one hundred and twenty-five grains of the salt to a pint of water. After this it is again washed and dried. The advantage derived from this method, is a more sensitive paper, and a more even distribution of the compounds over the surface.
Another deviation from Mr. Talbot's method has been suggested, as follows:
Brush the paper over with a solution of one hundred grains of nitrate of silver to an ounce of water. When nearly, but not quite, dry, dip it into a solution of twenty-five grains of iodide of potassium to one ounce of distilled water, drain it, wash it in distilled water and again drain it. Now brush it over with aceto-nitrate of silver, made by dissolving fifty grains of nitrate of silver in one ounce of distilled water, to which is added one sixth of its volume of strong acetic acid. Dry it with bibulous paper, and it is ready for receiving the image. When the impression has been received, which will require from one to five minutes according to the state of the weather, it must be washed with a saturated solution of gallic acid to which a few drops of the aceto-nitrate of silver, made as above, have been added. The image will thus be gradually brought out, and may be fixed with hyposulphite of soda. To obtain the positive picture, paper must be used brushed over with an ammonio-nitrate of silver, made thus: forty grains of nitrate of silver is to be dissolved in one ounce of distilled water, and liquid ammonia cautiously added till it re-dissolves the precipitate.
A pleasing effect may be given to calotype, or indeed to all photographic pictures, by waxing them at the back, and mounting them on white paper, or if colored paper be used, various beautiful tones of color are produced.
POSITIVE CALOTYPE.
At a meeting of the British Association, Professor Grove described a process by which positive calotype pictures could be directly obtained; and thus the
The calotype pictures when prepared as we have stated, possess a yellowish tint, which impedes the process of taking copies from them. In order to remedy this defect, Mr. Talbot has devised the following method. The calotype picture is plunged into a solution consisting of hyposulphite of soda dissolved in about ten times its weight of water, and heated nearly to the boiling point. The picture should remain in about ten minutes; it must then be removed, washed and dried. By this process the picture is rendered more transparent, and its lights become whiter. It is also rendered exceedingly permanent. After this process the picture may be waxed, and thus its transparency increased. This process is applicable to all photographic papers prepared with solutions of silver.
Having thus fully, and it is hoped clearly, considered the process, it may be necessary before dismissing the calotype from notice, to add one or two remarks from the observations and labors of some who have experimented in this art. Dr. Ryan in his lectures before the Royal Polytechnic Institution, has observed, that in the iodizing process the sensitiveness of the paper is materially injured by keeping it too long in the solution of iodide of potassium, owing to the newly formed iodide of silver being so exceedingly solvable in excess of iodide of potassium as in a few minutes to be completely removed. The paper should he dipped in the solution and instantly removed. There is another point, too, in the preparation of the iodized paper in which suggestions for a slight deviation from Mr. Talbot's plan have been made. In the first instance, it is recommended that the paper be brushed over with the iodide of potassium, instead of the nitrate of silver, transposing, in fact, the application of the first two solutions. The paper, having been brushed over with the iodide of potassium in solution, is washed in distilled water and dried. It is then brushed over with nitrate of silver, and after drying is dipped for, a moment in a fresh solution of iodide of potassium of only one-fourth the strength of the first, that is to say, one hundred and twenty-five grains of the salt to a pint of water. After this it is again washed and dried. The advantage derived from this method, is a more sensitive paper, and a more even distribution of the compounds over the surface.
Another deviation from Mr. Talbot's method has been suggested, as follows:
Brush the paper over with a solution of one hundred grains of nitrate of silver to an ounce of water. When nearly, but not quite, dry, dip it into a solution of twenty-five grains of iodide of potassium to one ounce of distilled water, drain it, wash it in distilled water and again drain it. Now brush it over with aceto-nitrate of silver, made by dissolving fifty grains of nitrate of silver in one ounce of distilled water, to which is added one sixth of its volume of strong acetic acid. Dry it with bibulous paper, and it is ready for receiving the image. When the impression has been received, which will require from one to five minutes according to the state of the weather, it must be washed with a saturated solution of gallic acid to which a few drops of the aceto-nitrate of silver, made as above, have been added. The image will thus be gradually brought out, and may be fixed with hyposulphite of soda. To obtain the positive picture, paper must be used brushed over with an ammonio-nitrate of silver, made thus: forty grains of nitrate of silver is to be dissolved in one ounce of distilled water, and liquid ammonia cautiously added till it re-dissolves the precipitate.
A pleasing effect may be given to calotype, or indeed to all photographic pictures, by waxing them at the back, and mounting them on white paper, or if colored paper be used, various beautiful tones of color are produced.
POSITIVE CALOTYPE.
At a meeting of the British Association, Professor Grove described a process by which positive calotype pictures could be directly obtained; and thus the