MONITORING THE FADING AND STAINING OF COLOR PHOTOGRAPHIC PRINTS
8 RECOMMENDED LIMITS OF COLOR PRINT IMAGE DETERIORATION
EXAMINATION OF A LARGE number of deteriorated color prints—including samples which were faded in accelerated light-fading and dark-storage tests and prints which slowly faded during long-term display and dark storage under normal conditions—has led the author to propose the set of limits for color print image deterioration shown in Table I. This set of four groups of data describes all of the significant visual changes that can take place when a color print deteriorates in dark storage and/or during exposure to light and/or ultraviolet radiation. Such changes include stain formation, density and contrast changes, color balance shifts, and the various common combinations of these changes. A color print may be considered to have passed the acceptable limit of deterioration when any one of the numerically expressed criteria has been reached. With any given color print material, the particular change involved depends on the particular conditions of display or dark storage. For example, with Polaroid SX-70 prints kept in the dark, the “minimum-density stain formation” limit will almost always be reached first. With Kodak Dye Transfer prints (made with the dye set commercially available in the 1965–1980 period) on display, the “red-green-blue density loss imbalances” limit will probably come first, because of the light-fading instability of the Kodak Yellow Dye Transfer Dye. This more complex analysis of color image deterioration correlates much better with visually observed changes than does the criterion “0.1 density loss of one or more dyes at an initial density of 1.0,” which has sometimes been used in the technical literature of the manufacturers.20 The “0.1 density loss” criterion also ignores stain formation, which is often the principal factor in color image deterioration in materials like Polaroid SX-70.
The author suggests, of course, that the limit of color image deterioration should not be reached during any single exhibition period and that color prints should not normally be placed on continuous display until the limit has been reached. Some types of chromogenic color prints, such as Kodak Ektacolor 74 RC prints, will pass the suggested limits of deterioration in less than 10 years, even when kept in the dark at room temperature, because of their poor dark-storage stability; this can be prevented only by placing the prints in low-temperature storage. The curator will have to decide how much of the useful life of a print he or she will allow to be consumed during a particular exhibit, or during the curator's tenure, and how much will be left for future curators. For example, given this set of deterioration criteria, and knowing the stability characteristics of Kodak Ektacolor 74 RC prints, one could conclude that under moderate-level tungsten illumination (200 lux/20 footcandles) and room-temperature conditions of 24°C (75°F) and 55% relative humidity, the print will have a useful display life of about 6 years; this would allow 24 three-month exhibitions if the print was kept in cold storage between display periods. If the print was not kept in cold storage, and instead was kept at room temperature, the useful life would probably be less than 8 years even if it was never exhibited. If the print was kept in cold storage between exhibitions, and was exhibited for a single three-month period each 5 years, the final exhibition of the print could take place about 120 years after the first exhibition. Other print materials (such as many of the early color processes) are much less stable than Kodak Ektacolor 74 RC prints and could tolerate only a fraction of this total display time.
Grant Romer, the conservator of photographs at George Eastman House in Rochester, New York, working in conjunction with the author and Ron Emerson, curator at George Eastman House, and John Upton, guest curator at the museum, will be using the basic color print monitoring procedures described here for “Color as Form: A History of Color Photography,” an exhibition which will open at the Corcoran Gallery in Washington, D.C., on April 9, 1982 and at George Eastman House on July 2, 1982. To the author's knowledge, this will be the first exhibition of color photographs to be monitored densitometrically during the exhibition period. Some of the photographs chosen for the exhibition will not be shown in their original form because of physical problems and/or the extreme instability of their color images; instead, color copy prints or transparencies will be displayed. Any of the original color photographs on display that change beyond predetermined limits will be replaced with copy prints during the 6-month period of the exhibition.