MONITORING THE FADING AND STAINING OF COLOR PHOTOGRAPHIC PRINTS
3 COLOR PRINT FADING MONITOR
USE OF A COLOR PRINT fading monitor allows one to measure indirectly the changes which take place in a color photograph. All of the colors and tones of a color photograph are obtained by varying the concentrations of cyan, magenta, and yellow image dyes or pigments in the emulsion layers which are coated in three or more layers on the surface of the support material. A few types of color prints, such as Fresson Quadrichromie pigment prints, make use of black as a fourth color; the black pigment is normally present only in high-density (dark) areas of the image. The same three (or four) colors are used to form all the colors in a color print, and a neutral gray patch consists of nearly equal concentrations of the three (or four) image dyes or pigments. The minimum-density patch contains little or no dye or pigment. It is possible to measure changes in neutral gray patches of minimum density, low density, and maximum density and thereby to obtain a reasonably accurate indication of changes occurring in any area of a color print if the three patches are made of the same print material and are processed in the same way as the original print. A single fading monitor should be used with only one color print, and the monitor should be permanently assigned to that print with a serial number.
Potential disadvantages of fading monitors include possible differences in print and monitor fading/staining rates which may be caused by differences in materials, processing, or use conditions. Furthermore, as noted above, monitors can be prepared only from print materials and processes which are available in the marketplace: monitors therefore cannot be prepared for most, if not all, older color print materials in a collection. Most institutions will find it more practical and accurate to monitor most of their color prints directly and to reserve the use of fading monitors for special situations; for example, in some cases it may be undesirable to remove a print from its frame repeatedly for direct measurements.