Paper Prints. — For paper prints there is nothing so good as gelatino- or collodio-chloride P.O.P. All processes which increase contrast or diminish detail must be classed as unsuitable ; thus we rule out bromide and gaslight papers. We have seen many stereographs on bromide paper, but not one that would not have been better on P.O.P. If gaslight printing must be resorted to, phosphate paper will be found to approximate most nearly to P.O.P. in gradation, tone, and rendering of detail. Whichever printing process is adopted, the paper should be of the glossy variety.
In making P.O.P. prints, continue the printing until the high lights have lost their whiteness. If, through undue contrast in the negative, this is not possible without clogging up the shadows, it is best to remove the print from the frame when the shadows are fully printed, and expose it boldly to the light until the white patches are slightly discoloured. The object of this " sunning down" is to prevent the snowy effect noticeable when slides of too contrasty a kind are viewed in the stereoscope.
A warm brown is, as a rule, the most suitable tone for stereographs, and care should be taken not to carry toning too far. After fixing and washing, hang the prints up to dry ; the natural gloss thus retained is preferable to the mirror-like surface got by squeegeeing.
Trimming and if ounting.—ln a contact print from a stereoscopic negative, the picture taken by the right-hand lens is on the left hand, and vice versa. Why this is so will be seen from the following diagrams (Figs. 60-62). Let us imagine the part of Fig. 6o marked " Left " to be an object as seen from the position of the left-hand lens, and the part marked " Right " to be the same object as seen from the position of the right-hand lens. The images thrown on the plate will be inverted independently of each other, and the negative, if looked at from the back, in the position it occupied in the camera, will be as Fig. 61, where, it will be noted, the outer edges, A, B, C, D, have become adjacent. On turning the negative right-way up, and making a contact print from it, we obtain the result shown in Fig. 62. Now, as it is necessary that the right-eye picture should be seen by the right eye, and the left by the left eye, the two sections of the print must be transposed before mounting. If this be neglected, the image obtained in the stereoscope will be inside out, as it were, the distance taking the place of the foreground, and the foreground receding into the distance. To guard against this
error, every print, before trimming is commenced, should be lightly marked on the back with a pencil stroke as shown at A B in Fig. 63. When, later on, the print is cut into two, a portion of the pencil mark will be on each section, serving to show which edges must be outermost when the prints are mounted.
Trimming may be done by the aid of glass trimming ! gauges, but better by means of a 5 in. trimming board with pivoted shear-blade, or a small Merrett trimming-desk. Both I prints must be trimmed to exactly the same size. The width , of either should not exceed 21. in. ; it may be as much less as the subject or the quality of the print demands. There is no need to include a defective edge or redundant marginal detail for the sake of full width. The height may be anything within the limits of the mount, and should be determined by the character of the subject. Many prints can be cut down to 2l in., or less, with advantage.
The two prints should coincide exactly as regards their upper and lower edges. In the case of the side edges a little variation may be introduced with good effect. if the inner edge of each print, as finally mounted, includes an eighth of an inch more of the photograph than the outer edge of the other print, the effect in the stereoscope will be that the entire view will appear to lie beyond the plane of the mount. (See illustration, " Guy's Mill.") This has been called the " window effect," because the sensation is that of looking at a view through an open window, of which the mount represents the frame. This method of trimming suits most subjects, but a contrary method is sometimes admissible in the case of flowers, still life, and small objects, the foremost parts of which may thus be made to appear nearer than the plane of the mount. Effective use has been made of this " dodge " in our second stereograph, " Floss." On viewing this stereoscopically, the dog appears to be standing with his head partly through the circular opening. It is a method which should only be used with great moderation, an exaggerated effect being anything but pleasing. The difference in the trimming, by either method, should be measured by the nearest foreground object.