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Types of Visual Aids and Their Uses 65
Nepera by volume with four parts of water. Place this solution in one of the small enameled trays. This quantity will be sufficient for developing sixteen to twenty slides, but should not be saved from day to day. After the lantern-slide plate has been exposed, remove it from the printing frame and slide it into the tray of developer, emulsion side up. The plate should be left in the developer from one to two minutes, and only experience will make it possible for the worker to determine just when it should be removed. It should be left in the solution until the picture shows clearly on the back of the plate. Usually further development will produce a fog.
Fixing. After developing, the slide should be rinsed in plain water and then placed in the acid fixer. It should be left in the fixer for twenty minutes. The fixing compound or "hypo" is available in onepound packages. The contents of a package should be dissolved in two quarts of water, following the directions which are printed on the outside. The "hypo" may be used several times and this quantity will fix about a hundred slides. The solution should be kept in a brown bottle or jar, which may be covered tightly, and should be stored in a dark place.
Washing and Drying. After about twenty minutes in the fixer, the slides should be placed in a tank and washed in running water for ten to fifteen minutes and then placed in a rack to dry. When more advanced work is attempted, it will be necessary to control the temperature of the solutions and water rather carefully; but for this elementary work, the usual temperature of tap water will be satisfactory.
Mounting Slides. When the slide plate is thoroughly dry, it should be projected in a lantern for examination. If it is clear and satisfactory, it is ready to be mounted for permanent use. A mat, which is a piece of black paper 3V4x4 inches in size with the center cut out in any desired shape and size, is placed next to the emulsion side of the slide. The opening in the mat is usually 2^4 or 2% x 3 inches in size. After placing the mat in position, a piece of cover glass, 3V4x4 inches in size, is placed over it to protect the emulsion from damage. The slide plate, the mat, and the cover glass are then bound together with a strip of binding tape.
If the mat has on it a small white or gilded spot or star, this spot should be placed at the lower left-hand corner of the plate. If there is no such mark on the mat, a small spot or square of gummed paper should be placed on the outside of the cover glass in the same position. This spot will serve as a "thumb mark" to the operator when