NOTES

1. Dark-fading is used as a general term to describe the kinds of color fading and staining which take place when light is not present; the rates of the chemical reactions involved in dark-fading are governed by temperature and, to a lesser extent, by relative humidity. The higher the temperature and the higher the relative humidity, the faster the rate of dark-fading. With many types of color prints, dark-fading rates approximately double for each 6�C (11�F) increase in temperature. As light is not involved in dark-fading, these chemical reactions continue in essentially the same form when a print is exposed to light on display. Light fading is the result of photochemical reactions. When a print is on display, light-fading and dark-fading occur simultaneously.

2. Chromogenic color prints, which are the most common type of color prints, contain no dyes prior to processing. The image dyes are synthesized in the thin gelatin emulsion layers by a process called chromogenic development. Exposed light-sensitive silver halide (silver chloride, silver bromide, or silver iodide) is developed in a color developing agent (usually a phenylenediamine) which produces metallic image silver and oxidized developing agent. The oxidized developing agent reacts with organic molecules known as color couplers (which are normally put into the emulsion layers during manufacture, or, as in the case of the Kodachrome Process, the couplers are dissolved in the color developers) to produce cyan (usually a indoaniline dye), magenta, and yellow (usually azomethine dyes). The metallic silver produced in the course of development is chemically removed by the end of processing; the color image consists only of the three organic dyes. For a detailed discussion of chromogenic development, see Grant Haist, Modern Photographic Processing, Vol. 2 (New York: John Wiley and Sons, 1979). While many types of colorants fade on prolonged exposure to light, the chromogenic dyes used with color photographs are distinguished by the fact that many of these dyes fade fairly rapidly during dark storage.

3. Henry Wilhelm, “Light Fading Characteristics of Reflection Color Print Materials,” presented at the 31st Annual Conference of the Society of Photographic Scientists and Engineers, Washington, D.C., May 1, 1978. Some of the information presented in the talk has been published: Henry Wilhelm, “Color Print Instability,” Modern Photography, vol. 43, no. 2 (February 1979), pp. 92–93, 118, 120–121, 124, 134, 138, 140, 142, 176.Possible reciprocity effects were mentioned by Robert J. Tuite, “Image Stability in Color Photography,” presented at the 31st Annual Conference of The Society of Photographic Scientists and Engineers, Washington, D.C., May 1, 1978. Tuite's talk was later published as “Image Stability in Color Photography,” Journal of Applied Photographic Engineering, vol. 5, no. 4, (Fall 1979), pp. 200–207.

4. An account of reciprocity effects in accelerated light-fading tests was given in Henry Wilhelm, “Reciprocity Effects in the Light Fading of Reflection Color Prints,” presented at the 33rd Annual Conference of The Society of Photographic Scientists and Engineers, Minneapolis, Minnesota, May 5, 1980. Some of the information in the talk has been published: Bob Schwalberg, “Color Preservation Update,” Popular Photography, vol. 89, no. 1 (January 1982), pp. 81–85, 131.Two articles of interest concerning high-intensity light fading tests of color photographs (possible reciprocity effects were not investigated):C.H. Giles, S.D. Forrester, R. Haslam, and R. Horn, “Light Fastness Evaluation of Colour Photographs,” The Journal of Photographic Science, vol. 21 (1973), pp. 19–23. (The light fading stabilities of certain unidentified color photographic materials were evaluated using the B.S.I. Blue Wool Standards as a means of comparison);H.G. Rogers, M. Idelson, R.F.W. Cieciuch, and S.M. Bloom, “Light Stability of New Polaroid Colour Prints,” The Journal of Photographic Science, vol. 22 (1974), pp. 138–142. (The authors were with the Research Laboratories, Polaroid Corporation, Cambridge, Massachusetts).

5. A project to monitor albumen prints was started at George Eastman House in Rochester, New York, in 1979 by James Reilly, Doug Severson, and Grant Romer. Both 19th-century and freshly made albumen prints (in the form of gray scales) were included in the project in an effort to gain a better understanding of the stability characteristics of this type of print. The project is still under way at the time of this writing.David Kolody, a private conservator from Boston, Massachusetts, has adapted the method of direct monitoring of prints described in this article to the routine monitoring of black-and-white photographs, lithographs, watercolors, and etchings. Kolody prepared a polyester overlay sheet marked with a grid consisting of numbered lines drawn 2 cm (� inch) apart and with holes cut at the intersections of each line. Density readings can be quickly taken at line intersection points on the grid which correspond to high-density, medium-density, and low-density parts of the image; the line coordinates and density data are recorded in a notebook. Only one overlay sheet need be prepared using this procedure; the same sheet is used for all of the prints being monitored. While the pre-drawn grid overlay sheet doesn't offer the flexibility of being able to locate the densitometer head at any desired point on a print, Kolody believes that the method is adequate for routine monitoring of work before and after conservation treatments; he started using the system in early 1982.

6. In 1966, Garry Thomson, scientific adviser to the National Gallery in London, started an investigation of methods to record changes in paintings and arranged for a specially designed spectrophotometer to be built for the purpose; certain paintings are now being measured once every five years. See Linda Bullock, “Reflectance Spectrophotometry for Measurement of Colour Change,” National Gallery Technical Bulletin, vol. 2 (1978), pp. 49–56. Also see R. M. Johnson and R. L. Feller, “The Use of Differential Spectral Curve Analysis in the Study of Museum Objects,” Dyestuffs, vol. 44, no. 9 (1963), pp. 1–10, and R.L. Feller, “Problems in Spectrophotometry,” in G. Thomson, (ed.), 1976 London Conference on Museum Climatology, IIC, 2nd ed. (London, 1968), pp. 196–197.

7. The companies include the Macbeth Division of the Kollmorgen Corporation, Little Britain Road, P.O. Drawer 950, Newburgh, New York 12550, phone: 914–561–7300, and Electronic Systems Engineering Company, East Airport Road, Cushing, Oklahoma 74023, phone: 918–255–1266. Reflection densitometers of good quality cost between $1,500 and $3,500, depending on the model. To monitor color transparencies, such as Autochrome plates or Ektachrome transparencies, a combination transmission/reflection densitometer should be obtained; both of the above companies supply separate and combination models.

8. Telephone discussion with Joseph P. Casscles, Service Specialist, Macbeth Division of the Kollmorgen Corporation, Newburgh, New York (January, 1982).

9. Matte surface polyester (such as DuPont Mylar or Cronar) sheets of a suitable type can be obtained from stores that sell drafting and engineering drawing supplies.

10. Densitometer head locations can be marked with a technical pen (such as a Koh-I-Noor Rapidograph) with a No. 1 point (medium) and a suitable stable black ink (such as Higgins Professional India Ink for Film No. 4465 Black, Koh-I-Noor Rapidograph “Universal” Waterproof Black Drawing Ink No. 3080-P, or Koh-I-Noor Rapidomat Black Ink No. 3074-F).

11. Holes in the polyester overlay sheet are best cut by placing the sheet on a large piece of glass and cutting out a circle with an X-ACTO Craft Swivel Knife No. 3241. As an alternative to round holes, square holes may be cut using a straight-blade knife. Be certain that the knife blade is very sharp and cut the holes carefully to avoid rough edges which might scratch the surface of a print.The author gratefully acknowledges the suggestion by Grant Romer, conservator at George Eastman House in Rochester, New York, that holes be cut in the polyester overlay sheet. Eliminating the polyester from the densitometer optical path improves the long-term accuracy of this system; it also permits the use of matte-surface polyester, which has ink adhesion far better than that of the normal high-gloss polyester surface. In the original version of the monitoring system proposed by the author in 1978, readings were made through a clear polyester overlay sheet.

12. Suitable polyester (DuPont Mylar-D) sleeves which open along one edge, like the pages of a book, so that it is not necessary to slide a print or film in and out (thus minimizing risk of scratching the print surface), are available from TALAS, 130 Fifth Avenue, New York, New York 10011, phone: 212-675-0718.

13. Inexpensive metal frames of the appropriate size can be obtained at many variety stores and, for large quantity purchases, one can contact a manufacturer such as Intercraft Industries Corp., Chicago, Illinois 60614. Backing materials supplied with such frames should be discarded and replaced with high-quality matte board.

14. Kodak Reflection Densitometer Check Plaque, Kodak Catalog No. 140–5026; for use with reflection densitometers. For transmission densitometers, obtain a Kodak Transmission Densitometer Check Plaque, Kodak Catalog No. 170–1986. Eastman Kodak Company, 343 State Street, Rochester, New York 14650.

15. Eastman Kodak Company, Evaluating Dye Stability of Kodak Color Products, Current Information Summary (CIS) No. 50, January, 1981. CIS No. 50 series stability information sheets are available for each Kodak still color film and print material; data are given for fading rates at normal room temperatures and for refrigerated storage. Contact Sheldon Phillips, Consumer/Professional and Finishing Markets, Eastman Kodak Company, 343 State Street, Rochester, New York 14650. Also see Storage and Care Kodak Color Materials, Kodak Pamphlet No. E-30 (12–1980 revision), and Charleton C. Bard, George W. Larson, Howell Hammond, and Clarence Packard, “Predicting Long-Term Dark Storage Dye Stability Characteristics of Color Photographic Products from Short-Term Tests,” Journal of Applied Photographic Engineering, vol. 6, no. 2 (April 1980), pp. 42–45.

16. The Macbeth ColorChecker can be obtained from photographic suppliers or from the M Division of the Kollmorgen Corporation, Little Britain Road, P.O. Box 950, Newburgh, New York 12550, phone: 914-561-7300.

17. The first art institution to have a humidity-controlled cold-storage facility will be the Art Institute of Chicago. The facility, under construction at the time of this writing, will be capable of maintaining a temperature of − 18�C (0�F) at 40% relative humidity; it is scheduled to be in April, 1982. At this writing, George Eastman House in Rochester, New York does not yet have cold storage facilities for its extensive collection of color still photographs and color motion pictures. Other collecting institutions which have low-temperature cold-storage facilities are the John F. Kennedy Presidential Library in Boston, Massachusetts (− 18�C [0�F], 30% RH, opened in 1979); National Aeronautics and Space Administration (NASA) in Houston, Texas (− 15�C [5�F], 25% RH, opened in 1982, replacing a facility which operated at 13�C [55�F], 50% RH, opened in 1963), and Time, Inc., Rockefeller Center, New York (− 18�C [0�F], 30% RH, to be operational in early 1982). Institutions with moderate-temperature cold-storage facilities include the Peabody Museum at Harvard University (3�C [37�F], 30% RH, opened in 1979); the Library of Congress, Landover, Maryland (2�C [35�F], 35% RH, opened in 1978); Human Studies Film Archive, Smithsonian Institution, Washington, D.C. (4�C [40�F], 50% RH, opened in 1975); Lyndon B. Johnson Presidential Library, Austin, Texas (10�C [50�F], 45% RH, opened in 1971); Gerald R. Ford Presidential Library, Ann Arbor, Michigan (4�C [40�F], 40% RH, opened in 1981). A rental cold-storage facility for the storage of color photographs and motion pictures (− 18�C [0�F], 30% RH) will open in Los Angeles, California, in late 1982: Jack B. Goldman, President, Advanced Media Archives, Inc., 96 Harvard Avenue, Brookline, Massachusetts 02146, phone: 617–277–5214.

18. Kodak Storage Envelopes for Processed Film, Kodak Catalog No. 148 6398 (size 4 � 5 inches), and Catalog No. 149 0028 (size 8 � 10 inches). These heat-sealable envelopes are made with an aluminum foil barrier; ordinary plastic bags readily transmit water vapor and are not suitable for the storage of photographs in uncontrolled humidity conditions. The Kodak storage envelopes are available from photographic suppliers or from the Eastman Kodak Company, 343 State Street, Rochester, New York 14650.

19. Documentation photography is most effectively done with color reversal films (such as Kodak Ektachrome 50 Professional Film). After processing, the color transparencies can be preserved by placing them in cold storage. The author believes that in most cases, color films stored under the proper conditions (− 18�C [0�F], 30% RH) will greatly outlast archivally processed black-and-white films stored under typical room temperature conditions. It is assumed here that an institution engaged in a monitoring program will have access to cold storage facilities for its collections, densitometer photographic calibration standards, and color documentation photographs.

20. See for example Robert J. Tuite, “Image Stability in Color Photography,” Journal of Applied Photographic Engineering, vol. 5, no. 4 (Fall 1979), pp. 200–207, and Evaluating Dye Stability of Kodak Color Products, Kodak Publication CIS-50, January, 1981, Eastman Kodak Company, 343 State Street, Rochester, New York 14650.