This section is from the book "Complete Self-Instructing Library Of Practical Photography", by J. B. Schriever. Also available from Amazon: Complete Self-Instructing Library Of Practical Photography.
Retouching The Prints. It frequently happens that by mischance some of the coloring matter has been removed from the print during development. The color can be readily replaced and the damage made good by removing a little of the color on the edge of the paper; or it is better still to have a little extra sheet of paper coated at the same time as the original print. The color on this little extra piece of paper, when placed in water, will soften and can be removed with the brush to the original print, to make good any damage. This is a better method than to wait until the print is dry and then to mix colors to match.
Clearing The Print. Though not entirely necessary, it is often a good plan to place the print in a 5% solution of alum, for the purpose of clearing out any of the chemicals that may be left in it. A short ten-minute bath is all that is necessary. It is best to give the print the alum bath after it has once dried, for then there is no danger of any more color being dissolved away.
Multi-Coated Prints. The best workers in gum-bichromate frequently prefer to give the paper two or three coatings of pigment and gum, developing each coating by itself. A light coating is first applied to the paper in the previously described fashion, and a weak print obtained, with clear high-lights. When dry the paper can be coated a second time, and again printed, some method being used for registering the paper on the negative. The exposed print is developed and dried in the usual manner, and then a third coating is applied, in order to obtain body in the shadows. This need not be fully printed, and a careful worker can retain the color in his shadows and wash away
152c the color on the high-lights, and half-tones, thus obtaining a print with greater strength all over.
Shrinking The Paper. Where more than one coat of pigment is applied to the paper, or with papers that are liable to shrink after having once been wet, it is best, before coating, to shrink the paper thoroughly, which can be effected by leaving the sheet of paper in cold water for at least half an hour, and then after blotting the surface moisture off hang up to dry. Such paper will not be liable to shrink to any perceptible extent during the subsequent manipulations.
Registering The Paper On The Negative. There are several methods of registering paper on the negative when the former has to be printed several times.
457. Method No. 1. - A printing frame some sizes larger than the negative being printed from must be used. Procure a sheet of stout cardboard the same thickness as the negative. Cut out the center of the cardboard to tit snugly around the negative, and then with a large sheet of glass in the printing frame, as a support, place the cardboard and negative in the frame. Now, adjust your coated paper to the negative, and at the sides draw lines across the paper, extending onto the cardboard. When the paper is being printed a second time these lines on the back of the paper and on the cardboard must correspond.
458. Method No. 2. - With the sheet of cardboard as before, insert from the back of the cardboard, about an inch away from each end of the negative, very small drawing pins, so that when the cardboard and negative are in the printing frame the points project upwards slightly. Now, place your paper in the negative and these sharp points will make small holes in the paper. For the second and third printings the paper must be placed on the negative so that the small holes coincide with the pin points. The registering of the prints over the negative will then be sufficiently accurate.