LANTERN SLIDES, MASKING, BINDING, AND SPOTTING When a lantern slide is developed, fixed and washed, it requires finishing in such a manner that it can be shown effectively in the lantern, and handled without injury. The picture requires masking, that is, the portion of the plate not required needs to be covered with opaque paper, so that the picture is isolated on a dark screen, the edges being sharp and trite as in a well-trimmed print. Lantern-slide masks are obtainable with openings of various shapes and sizes, but a serious worker soon finds it difficult to adapt them to his requirements. A print should be trimmed to a nicety, so as to include the amount of subject desired, and no more. Using commercial masks is like using untrimmed paper of a uniform size for prints ; while it might answer in many cases, it fails frequently. A favourite plan with some workers is to cut a number of slips of thin opaque paper slightly less than 31 ins. long, and varying in width from in. to + in. Pour such slips can be attached to the film of the slide with a touch of gum at each corner, they can thus be arranged to cut off the subject exactly as required. By keeping these slips true to the edges of the plate, rect= angularity of the opening is secured.
Before or after binding, the slide requires spotting. Two prominent spots have to be applied for the purpose of indicating to the lanternist the correct position for inserting the slide in the lantern. These spots must be at the two top corners on the face of the slide, film side towards the operator.
There are two methods of binding a cover glass to the face of the slide so as to protect the film from injury. The first is adopted by those who make lantern slides commercially on a large scale. A strip of gummed paper about 15 in long is moistened and attached to the four edges of the two plates, the corners being ,deftly mitred. The second method is to apply four separate short slips, one for each side, and it is much easier to bind a slide neatly and securely by this method. Short binding slips for attach ing in this manner are obtainable, or binding slips may be made by the worker. A thin paper should be used, and gum has to be applied when ready for using. An advantage of cutting binding slips is that they may be made wider, and so hold the plates together more firmly.