associated  with  the  picture  can  be  heard  during playback Floppy  disks  used  in  electronic  imaging  can  be reused for endless times-the same as any other magnetic recording medium. No chemicals or darkroom tech- niques are required to produce these images. Once the image  is  captured  on  the  floppy  disk,  it  can  be transmitted  over  the  telephone  lines,  edited,  and  printed using a video printer-all under normal room-lighting conditions. BLACK-AND-WHITE PRINTING PAPER The  performance  and  use  of  black-and-white photographic  printing  paper,  like  black-and-white  films, depends on the characteristics of the paper material. While the many types of photographic papers differ in their characteristics, they all basically consist of the emulsion on a paper support or base. Photographic printing papers (both black and white and color) are manufactured in both various cut sheet sizes, ranging from 5x7 to 20x24 inches and rolls up to 1,000 feet long. Photographic   papers   used   in   Navy   imaging facilities  are  either  coated  with  polyethylene  or  are resin-coated. These papers are coated on both sides of the base. This clear coating is treated so the paper does not stick to the surface of other prints during processing. Polyethylene-coated  papers  (manufactured  by  Ilford) can be marked on with pencils and pens. Coated papers have  water-resistant  bases  that  provide  short  processing times.  Most  black-and-white  papers  with  these  coatings have developing agents incorporated in the emulsion. The developing agents are activated when the paper is exposed  to  an  alkali  solution.  The  characteristics  of resin-coated paper make it ideal for machine processing, but they may also be tray-developed in a regular print developer. The image on black-and-white film is usually negative or recorded in tones of gray in reverse of the reflective brightness values of a scene. When the negative image is projected onto black-and-white paper, the resulting image is positive or recorded in tones of gray relative to the reflective brightness values of the original  scene.  A  negative  is  usually  used  or  viewed  by transmitted light. A paper print (or simply a print) is usually viewed by reflected light and may be referred to as  a  reflection  print  or  reflection  positive. Emulsion   Sensitivity The emulsions used for printing paper are much slower (less sensitive to light) than most film emulsions. Figure 2-7.–Cross section of variable-contrast black-and-white paper. A high sensitivity to light is not needed. Prints are often manipulated by providing additional exposure or by holding back exposure to selected areas of the print. If the paper emulsions were fast, exposure times would be extremely short and print manipulation would not be possible. The color or spectral sensitivity of a paper emulsion indicates the response to specific colors of light or radiation-the same as that for a film emulsion. The terms colorblind,  orthochromatic,  and  panchromatic  are  also used to describe the spectral sensitivities of paper emulsions.  The  response  of  a  paper  emulsion  to wavelengths  other  than  ultraviolet  radiation,  violet,  and blue light is achieved by the addition of sensitizing dyes to  the  emulsion  during  manufacturing. The ranges of sensitivity for all paper emulsions begin  in  the  near-ultraviolet  region  of  the  invisible portion  of  the  electromagnetic  spectrum.  The  color sensitivity of undyed silver emulsions extend to blue and blue-green. Panchromatic printing papers are sensitive to ultraviolet radiation, violet, blue, green, and red light. The color sensitivity of a black-and-white paper is NOT a determining factor for selecting a paper to print a specific  black-and-white  negative.  Panchromatic papers,  however,  are  normally  used  to  produce black-and-white  prints  from  color  negatives.  Color sensitivity DOES determine whether or not a safelight is required an, if so, what color of safelight can be used. Variable  Contrast  Papers Variable contrast papers are used almost exclusively in Navy imaging facilities. The contrast of the print image on variable contrast papers is controlled by the specific color of the exposing light. Variable contrast papers have two emulsion layers. The top layer is a high-contrast emulsion and is sensitive to blue light. The second emulsion layer is a low-contrast emulsion and is sensitive to green light (fig. 2-7). When a normal contrast  negative  is  exposed  through  a  variable  contrast filter with blue light, a harsh, contrasty print is produced. 2-9