A few general hints, which will not be repeated in the other papers, are as follows:
1. See that all dishes and utensils used in the preparing of solutions are perfectly clean. The traces of chemicals used in some other process left in the dishes will sometimes spoil the entire solution.
2. Follow the directions exactly. In the preparation of sensitizing solutions one must be careful to put in the amount given, and no more.
3. In handling chemicals care must be taken not to get any on the hands if one has a wound or sore. Some chemicals are very poisonous, and some are quite harmless, but by using rubber finger-tips one will not only avoid all danger of blood-poisoning, but will keep the fingers free from stains.
With the salts of uranium one may obtain several colors by treating the prints with different solutions in developing. To make red prints, take suitable photographic paper—which may be found at any dealer in photographic goods all ready for sensitizing—and sensitize it as follows:
Make a solution of 96 grs. of nitrate of uranium and 4 oz. of distilled water. Put in a flat tray, and float the paper on this solution for twenty seconds; drain, and dry it in a dark room. If the paper is dried by artificial heat it is much more sensitive to the light. As soon as the paper is thoroughly dry, cut it in sheets a suitable size for printing, and wrap first in post-office paper, and then in black needle-paper, and lay away in a drawer or covered box till wanted.
To print, place in the printing-frame and expose to the light. If the negative is thin, three minutes in bright sunlight will be sufficient, or one hour in the shade or on a dull day. If a strong negative is used, expose for ten minutes to bright sunlight, or two hours in the shade. Negatives vary in the time required to print from them, and the printing may be judged by the time which it takes to print with other papers, and gauged accordingly.
Have ready a solution of red prussiate of potash, made with 80 grs. of red prussiate of potash and 8 oz. of distilled water. As soon as the print is removed from the printing-frame wash it for twenty-five or thirty seconds in hot water (120° Fahr.), then place it face up in a toning-tray and flood it with the potash solution. Keep the tray in motion so that all parts of the paper may be affected equally. In a few moments the picture will begin to appear, and will develop into a beautiful blood-red color. As soon as the right tone has been reached and the detail is well out, remove from the solution, and wash in several changes of water till no trace of coloring matter shows in the water. Pin the print by the corners to a flat board, and set the board in an upright position till the prints are dry. These pictures may be applied to glass by optical contact, as described in No. 788.
One of these colored prints makes an attractive decoration for the cover of a collection of photographs. Make the cover of heavy water-color or picture-mat paper; cut a square in the upper right-hand corner, and place the picture back of the opening. Letter the cover in red, and tie with red ribbon or heavy red silk cord.