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.
Ruby Light. As the dry plate on which the image is to be photographed is extremely sensitive to all white light, only non-actinic light - i. e., light that has no appreciable effect on the plate - can be employed in handling it. Such light should be of a ruby color, or reddish yellow, and is usually obtained from what is called a dark-room lamp. There are many kinds of good dark-room lamps, arranged to burn oil, candles, gas, incandescent light, etc., and these are fitted with glass specially colored to give the correct kind of light for handling the plate. A lamp burning kerosene, or fitted with a bulb for an incandescent lamp, is the most satisfactory to use, candle lamps not being so satisfactory. (See Illustration No. 13, of an inexpensive darkroom lamp.)
Developing Outfits. A few essential pieces of paraphernalia which every amateur should possess for the development of the exposed plate, are a good ruby lamp, four or five trays, to fit the size of plates or films used - one tray to be used only for developing, another for fixing only, the other two or three trays for washing and after manipulation ; one graduate, about 8 ounces in size, one stirring rod, and a camel's hair brush.
101. The essential chemicals for the beginner are the developing powders and hyposulphite of soda for fixing. Later when preparing the solutions from the separate ingredients, it will be necessary to have the required chemicals.
Opening Of Box Of Plates. Plates of American manufacture are packed back to back in boxes of one dozen each, the faces being slightly separated by a small piece of cardboard, and are protected from the light by a double cover. To open the box, run a knife blade along the under edge and cut between the two layers of cardboard which form the two covers. This operation can be done in the white light, but neither cover should be removed outside of the dark-room. Before removing the covers of the box of plates the ruby lamp should be lighted, as it is necessary to have illumination of some kind by which to work. Previous to closing the door, remove the slides from the plate holders and carefully dust both the slides and the interior of the holders.
Loading The Holders. When ready to load the holders, having entered the dark-room and closed the door, remove the covers from the box of plates and turn back the black paper in which they are wrapped. The top plate will be face or film side down. Pick this plate up by the edge, being extremely careful not to touch either surface. At the lower end of the holder is a spring. Place the edge of the sensitive plate, with the film side out, against the spring, and press down on the spring until the plate drops into place. In some plate holders the spring holding the plate in place is controlled by a little metal lever on the outside or edge of the holder. By pulling down on the lever on the right hand side, it presses down the spring and the plate falls into place. After the plate is in place, press the lever back into position, when the plate is secured. (See Illustration No. 17 - loading the ordinary holder.)
104. After loading one side of a plate holder, carefully draw the camel's hair brush over the surface of the plate, to remove any dust which may have accumulated on its surface. With the light colored side facing out, insert the slide in the slot at the end of the holder, thus covering the sensitive plate. Proceed in like manner to load the other side of the holder, as well as the remaining holders. The second plate in the box will be face or film side up, the third plate film down, etc. Carefully replace the covers in proper order on the box of plates, after all holders are loaded. Then the door of the dark-room may be opened and the ruby light extinguished.