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.
Preparing The Cover-Glass. When the slides are thoroughly dry they are ready for mounting (or binding), and should be provided with cover-glasses, to protect them from scratching. Before covering they must be suitably masked and also spotted. These cover-glasses are merely plain pieces of thin glass, the exact size of the lantern-slide, 3 1/4 x 4 inches. They are known as lantern-slide cover-glasses, and are furnished in one dozen or gross packages. For the first experiments it will not be necessary to purchase cover-glasses, but use spoiled lantern-plates in their place, as, naturally, some of the plates which are exposed will not be worthy of being bound or covered at all, and those plates may then be used for cover-glasses, after removing the film. To remove the film from the plate first soak the plate in cold water for an hour or two, and then change to hot water. This treatment will remove the entire film from the glass; then a slight scrubbing with warm water, soap, and a nail-brush, followed by rinsing in cold water, will give you cover-glasses ready for use.
Masking. The mask, or mat, as it is sometimes called, should be made of some thin, strong opaque paper. The best is black needle paper, which is tough and thin. Regular masks can be purchased with openings of any shape desired. (See Illustration No. 21.) If you wish to make the masks, cut the paper the size of the plate, 3 1/4 x 4 inches; then cut out of the center the size and shape the view requires.
952. Write on one side of the paper mask, with white ink, the title of the slide, or any information regarding the scene. Do this writing in the upper portion, where it can be referred to when exhibiting. Fit the mask to the film as desired. When the slide is bound, apply a small gum sticker to the lower right-hand corner of the cover-glass, where it is used for numbering the slide. It also serves as a guide for inserting in the lantern, because when placing it in the lantern the slide is inserted top side down, with the white sticker at the top left-hand corner. This sticker indicates to the operator of the lantern the right way of inserting the slide-always inserting it with the white sticker at the upper left-hand corner facing the screen.
Illustration No. 21 See Paragraph No. 951.
953. The Ideal Mat is made of superior paper, which is especially manufactured for this purpose, the specific qualities being its water-proof finish, opaqueness and toughness. It is a solid black throughout, and a neat silver design is printed on one side. Another very good mat is the In-gento made of opaque paper, black on face, unprinted, and white on the back.
954. Both styles of mats are cut with the greatest accuracy, each opening being exactly in the center, cleanly cut, and devoid of ragged edges. All square openings are uniform in size, both in height and width, a feature which is greatly appreciated by all operators. These mats are manufactured in twenty different shapes and sizes of openings.
Illustration No. 22 McCormick's Lantern-Slide Mats See Paragraph No. 955.