LANTERN SLIDES, DIAGRAMMATIC Lantern slides of diagrams and other line sub jects may be made in many ways, as, for example, the following : (a) Copying through the camera and printing the slide by contact from the nega tive ; (b) printing from the drawing itself, which serves as a negative ; and (c) the use of specially prepared glasses on which the diagrams may be drawn direct and serve as slides.
(a) The copying of the diagram through camera is advisable in most cases, because the image can be reduced if necessary so as to come well within the limits of a lantern slide. Take care to obtain strong contrasts—the whites opaque and the lines clear. Should it be desired to show the diagram reversed as regards white and black—that is, white lines upon a black ground—the negative itself may be cut down to 3+ in. square and used as a slide, or the diagram may be copied on a lantern slide direct, through the camera.
(b) The second method is of particular service when drawings are to be made specially for lan tern slide work. A piece of white paper, thin and comparatively grainless, is cut to the size of a lantern slide. The drawing is then made on the paper in black ink, and used as a negative, . lantern slide being placed in contact with it and printed in the usual manner. The slide will
show the blacks and whites reversed. Should a black line slide be required, the slide just pre pared may be used as a negative and another slide printed by contact from it.
(c) This is not strictly a photographic process. Plain glass plates are coated with ground glass varnish, made as follows : Sandarac . . too grs. 23 g.
Gum mastic . too „ 23 „ Methylated ether . to oz. t,000 ccs.
Benzole 2 >, 200 When dry it gives a surface which takes the pencil well, and any drawing or writing may be made. The slide may then be made transparent again by flooding with : Sandarac . . 15o grs. 34 g.
Gum mastic . 15o „ 34 1, Methylated ether to oz. t,000 ccs.
which destroys the grain and leaves the drawing on what appears to be plain glass. Another plan is to use a special ink (see " Ink for Glass, etc."), while another is to use the finest ground glass obtainable, and after making the drawing, to destroy the grain by coating it with gum dammar dissolved in benzole. If white lines on a black ground are wanted, plain glass plates may be smoked by holding them over burning camphor, or by coating them with Brunswick black or other opaque pigment, and then scratching with a needle-point.