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.
878. It is essential that the negative, from which the slide is to be made, faces the clear sky, without any obstruction, such as trees, buildings, etc. Such obstructions injure the light by false reflections, or by cutting off the light, reducing its intensity. If an unobstructed view of the sky cannot be had, then a simple reflector can be constructed, by placing a large white cardboard outside the window, at an angle of 45°. This will evenly reflect a good strong light over the entire negative.
Use Of Artificial Light. The method employed for daylight work can be followed in making slides from negatives by artificial light. A large kerosene lamp, electric or gas-light can be used instead of a window. When a kerosene lamp or gas-light is used, neither one should be placed close to the negative, as the light will not be evenly distributed; but arrange the ends of the box so that the light will be reflected to the rear, and then work by reflected light.
880. It is well to place a reflector behind the lamps, to throw light against the asbestos. This will strengthen the light and also give a more even illumination. An apparatus is shown in Illustration No. 19 for the use of gaslight.
In this case there are two lights, one placed in each end of the box. The box is made of tin, curved so as to reflect the light uniformly onto the negative. The front being fitted with a ground-glass, all that is required is to place the negative in a printing-frame, with the thickness of the frame between the ground-glass and negative; place your copying-board against this light and extend the camera to a distance sufficient to give you the necessary focus. Finally extend the strips from camera to the negative frame, cover with opaque cloth, and all is ready for the exposure. (See Page 282.)
Making Slides From Copies. To copy a picture and from this copy make a lantern-slide, first make a negative from the picture. Proceed exactly as for copying an ordinary picture (See instructions on Copying). The picture must be copied the exact size of the lantern-slide, which is 3 1/4 x 4 inches, allowing 1/4 inch margin for the mask on the slide. The plate should be developed in the ordinary way. Carry the negative to the same strength in development as though prints were to be made from it. When the negative is dry, make the lantern-slide, using the method already described for contact printing.
Plates To Use. In the producing of perfect lantern-slides it is essential to use plates especially prepared for this purpose. These plates are made of extra thin glass, and are coated with a special emulsion which is very thin and has little or no grain. Almost all manufacturers of dry plates make lantern-slide plates. These have an emulsion, on which rich, black tones can be produced. There are also a number of brands on which the tones can be varied from black to brown, simply by changing the developer. The beginner is advised to use the ordinary lantern-slide plate, which can be purchased from any photo-supply dealer.
883. For the beginner who has had no experience, the regular dry plates are best for the first experiments, as they cost less than the lantern-slide plates, and are generally much more simple to handle. After becoming familiar with the work, the plates made for the purpose should be used.