Talking pictures : how they are made, how to appreciate them (c. 1937)

Developbig the Film When the developing process is finished, the film loops into another tank containing a second chemical formula known under the trade name of hypo. This is called a fixing bath because it stops the action of the developing fluid and permanently fixes the image on its celluloid base. The loops then go into a third series of tanks where water washes off the hypo. The looping continues through a high glass case in which brilliant electric lights, plus a current of warm air dries the film as it moves up, then down, then up. Finally, dry and in finished form, it comes out of the cabinet and is wound on a reel. The time elapsed has been about forty-five minutes, in which it took 2803.25 feet of unbroken film to span the physical length of sixty feet between the beginning and the end of the developing machine. But before developing can be done, printing must occur. It will be remembered that a picture is not an uncut piece of celluloid, but a series of perhaps five hundred separate pieces of film, scenes and subscenes, fastened together to form an entirety. These scenes may differ greatly in their lighting values. For each scene a "light test" is made. On this strip are thirty "frames," or separate pictures, each of the same image. Each frame has been printed at a different gradation of light. The frames are very dark at the bottom of the test strip and very light at the top. The laboratory superintendent selects by number the frame which gives the best light values. Naturally he would choose a different number for a moonlight scene from one he would use for a scene taken in the glare of a Sahara sun. [231]