To all to whom these presents shall come:
Be it known that I, James A. Cutting, of Boston, in the County of Suffolk and State of Massachusetts, have invented certain improvements in making photographic pictures, and that the following is a full, clear and exact description of the principle or character which distinguishes them from all other things before known, and of the usual manner of making, modifying, and using the same.
My improvements relate to that class of photographic pictures in which the pictures are obtained upon a prepared film of glass or other substance.
The film which I employ is collodion, and in order to insure success, the collodion must be prepared after my own process, as follows: Take 3 ounces (Troy) of pure dry nitrate potassa, and pulverize in a clean glass mortar; add to this 2½ ounces, fluid measure, of pure sulphuric acid, and stir the mixture with a glass rod; immerse in this liquid, 80 grains of clean, dry cotton, and knead the mass of cotton in the liquid for about Ave minutes; remove the cotton and quickly wash it, till every trace of acid is gone, and it must then be dried quickly—for I have discovered that the more rapidly the cotton is dried, the more sensitive the collodion; and I have found the best effects produced by displacing the water from the cotton by strong alcohol.
To prepare the collodion, take 10 ounces concentrated sulphuric ether, 60° Baumé, and mix this with 6 ounces of 95 per cent. alcohol. To this mixture add the prepared cotton, in quantity sufficient to make a collodion as thick as it can, and yet at the same time flow evenly over the surface of glass. Let it settle clear, and decant the solution.
In order to "excite" this collodion, take a deep 1 ounce vial—introduce 2½ grains of bromide of potassium, and add water, drop by drop, to make a saturated solution. In this solution dissolve 2½ grains of iodide of potassium, then add 1 ounce of collodion, and shake well. Let it settle clear and decant for use.
The solution must be decanted every day. In order to make the most sensitive collodion, I dissolve the bromide and iodide of potassium and the collodion[G] in a saturated solution of carbonate of ammonia in water. In using this collodion, pour it upon a clean glass plate to form a film in the usual way, and as soon as the collodion has set, and before it becomes dry, immerse the plate in a bath of nitrate of silver, made with 30 grains of nitrate of silver, 2 grains of iodide of silver, and 1 ounce water. Take the plate directly from the bath to the camera, and after sufficient exposure, the plate is taken to a dark room to develope the impression with the following solution: 'Take pyrogallic acid, 4 grains; acetic acid, No. 8, 1 ounce; dissolve and filter. For use, take of this liquid 1½ drachms, diluted with 6½ drachms of water, and when the impression is sufficiently developed, pour off the liquid, and immerse the plate in a solution of the hyposulphite of soda, 4 ounces to the pint of water. Wash the plate with pure water, and dry it in the usual way.
[G] This is a mistake: the collodion is not to be dissolved in the "carbonate of ammonia in water," but only the bromide and iodide of potassium. I called Mr. Cutting's attention to this, and he said I was correct.—S. D. H.
The advantages of the above process are, the brief time required to produce an impression, and the sharpness of the pictures. Portraits can be taken with as much facility as with the Daguerreotype, and the pictures are sharp and of excellent tone. The impression thus obtained is negative, and the positive picture is produced in the usual way. I denominate this the mezzographic process.
What I claim as my improvements in the process of obtaining photographic pictures, are—