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.
Mccormick's Self-Adjusting Lantern-Slide Mat. For matting lantern-slides the Obrig Camera Co.'s (N. Y.) McCormick "Self-Adjusting" is the most perfect mat made. With it one can compose perfectly the scene on the lantern-slide, and then have the slide matted accordingly. As will be seen on referring to Illustration No. '32, the mats are L-shaped, two of them being required to mat one slide.
The slide-maker can obtain rectangular openings of any dimension on his slides, with perfect corners and margins, and with infinitely less time and trouble than with any other device on the market. Full directions come with each pad of mats. Assuming the perpendicular and horizontal lines of the picture are paralled with the edges of the plate, one section of the mat is placed in contact with the film (the film side of the plate being held away from you), paralleling the inner edges of the mat with the edges of the slide. When the exact position required is obtained, moisten the surface of the slide a little, under the mat, to fasten in position. Adjust the other half by the score lines. Fasten as above, then cut away outside margins, when the slide is ready for binding. Small negatives may be matted for printing purposes, in the same manner, with these mats.
Mounting. Having the mask complete, lay the transparency plate, film side up, on a clean and flat surface. Next place the mat in position, and on this place the cover-glass. Care must be exercised that no dust or lint be bound up between the two glasses. After placing the mask and cover-glass in position, bind them together firmly with adhesive strips on all four ends.
Illustration No. 23 Ideal Lantern-Slide Vise See Paragraph No. 961.
957. In placing the cover-glass over the slide, the transparency and cover-glass must curve the same way, thus allowing them to be bound tightly together without breaking. The difficulty is to make the binding strips, or adhesive paper, adhere smoothly and firmly, but after a little practice and experimenting with two plain pieces of glass the proper way is acquired. This gummed strip should be thoroughly moistened with a damp sponge and made quite limp, to work to the best advantage, and must be watched closely while drying, to avoid wrinkles. Keep all parts in contact.
958. When prepared masks are used, the mask must be carefully adjusted until the opening is exactly where it is required, and then the mask is prevented from shifting by slightly moistening the surface of the slide under the mat. When this is dry, any part of the mask which projects beyond the slide may be trimmed off with a pair of scissors, and the slide is then ready for binding.
959. It is often possible to improve a commercial mask for some particular subjects, by sticking a strip of binder across it so as to narrow the opening; or, two masks may be crossed, one with the opening vertical and the other horizontal.
961. In Illustration No. 23 is presented a very ingenious little instrument, called the Ideal Lantern-slide Vise. By the use of this vise the mat is held in close contact with the lantern-slide and cover glass, leaving both hands free to manipulate the binding strip. When the slide is clamped between the rubber discs, it may be revolved to facilitate the operation of binding.
Illustration No. 24 The Ideal Binding Strips See Paragraph No. 964.
962. The tape is applied by starting at one corner, tacking the corner securely, then continuing all the way around, to the corner started from. Do not overlap the tape, as the overlap may add sufficient thickness to the slide to interfere with its working in the machine.
963. Where the slides, are mounted by hand (without the vice), it is best to bind the two opposite edges first, and allow them to dry before binding the remaining two edges. The cutting of the corners should be exact, so there will be no overlap.