THE EFFECTS OF FOUR DIFFERENT WET TREATMENTS ON ALBUMEN PHOTOGRAPHS
VALERIE BAAS, CHRISTOPHER FOSTER, & KAREN TRENTELMAN
ABSTRACT—The effects of different aqueous baths on the extent of surface deterioration in albumen prints were studied. Albumenized paper was sensitized, exposed, and processed. Four immersion media were used: deionized water, ammoniated deionized water (pH 9), a deionized water:ethanol mixture (1:1 v:v), and deionized water followed by ethanol. Groups of prints were treated repeatedly in each of the four baths. Drying was limited to a single method. Changes in the gloss of the albumen prints were measured at regular intervals with a glossmeter. Other changes in surface characteristics were monitored by visual and microscopic examination and phtomicrography. The effects of the different baths on the albumen layer, as well as factors such as differences in thickness and the comparative rates of wetting and drying, are discussed.
TITRE—Les Effets de Quatre Diff�rents Traitements Aqueux sur les Photographies Albumin�es R�SUM�—Les effets de diff�rents bains aqueux sur l'�tendue de la d�t�rioration de la surface des tirages � l'albumine ont �t� �tudi�s. Du papier albumin� a �t� sensibilis�, insol� et d�velopp�. Quatre bains de traitement ont �t� utilis�s: eau d�min�ralis�e, eau d�min�ralis�e ammoniaqu�e (pH 9), un m�lange d'eau d�min�ralis�e et d'�thanol (1:1 v:v), et eau d�min�ralis�e suivie d'�thanol. Des groupes de tirages ont �t� trait�s plusieurs fois dans chacun des quatre bains. Une seule technique de s�chage a �t� utilis�e. Les changements de brillance des surfaces ont �t� mesur�s � intervalles r�guliers avec un lustrom�tre. Les autres changements ont �t� observ�s par examen � l'oeil nu, au microscope et avec des photomicrographies. L'auteur discute les effets des diff�rents bains sur la couche d'albumine, ainsi que d'autres facteurs tels que les diff�rences d'�paisseur et les vitesses comparatives du mouillage et s�chage de cette couche.
TITULO—Efectos en fotograf�as a la alb�mina de cuatro tratamientos acuosos diferentes. RESUMEN—Se estudiaron los efectos de diferentes tratamientos acuosos en relaci�n al deterioro de las superficies de fotograf�as a la alb�mina. El papel albuminizado fue sensibilizado, expuesto y procesado. Se utilizaron cuatro medios de inmersi�n: agua deionizada, agua deionizada amoniatada (pH 9), una mezcla de agua deionizada y alcohol (1:1 v:v) y agua deionizada seguida de etanol. Grupos de copias fueron tratadas repetidamente en cada uno de los cuatro ba�os. El secado se limit� a un solo m�todo. Los cambios en el brillo de las copias de alb�mina se midieron en intervalos regulares con un medidor de brillo. Otros cambios en las caracter�sticas superficiales fueron observados por medio de examen visual y microsc�pico y fotomicrograf�a. Los efectos de los diferentes ba�os en las capas de alb�mina, as� como factores tales como diferencias en espesor y las relaciones comparativas de secado y mojado son discutidas.
It has long been thought that moisture may be detrimental to albumen photographs. Cracking and roughness (Messier and Vitale 1994; Vitale and Messier 1994) and fading (Reilly 1980) are all believed to increase due to the changes that occur in the albumen layer and paper substrate when subjected to cycles of wetting and drying. The dissimilar responses of gelatin emulsions and their paper substrates when exposed to varying moisture levels have been demonstrated to promote significant stress levels and crack formation in photographic prints (McCormick-Goodhart and Mecklenburg 1992). The deterioration of albumen prints may be produced by a similar mechanism.
The study presented here is an expansion of the work by Paul Messier and Tim Vitale (1994; Vitale and Messier 1994), in which they found increased cracking in albumen prints subjected to aqueous treatment. Messier and Vitale found that both the number and the dimensions of minute cracks in vintage albumen prints increased significantly after treatment with water, whether by immersion or damp surface cleaning. This effect is cause for concern, since it is sometimes necessary to use moisture in the treatment of albumen photographs. Wettings over the course of a typical photograph treatment might include damp surface cleaning, aqueous backing removal, aqueous adhesive removal, aqueous stain reduction, humidification and flattening, and lining or mounting with aqueous adhesives.
This project was designed to indicate which aqueous immersion media might be the least harmful to albumen prints. The four baths chosen were:
- deionized water
- ammoniated deionized water (pH 9)
- a deionized water:ethanol mixture (1:1 v:v)
- deionized water followed by immersion in ethanol.
An exaggerated treatment program was designed to more easily relate the degree of deterioration of the albumen layer to the different baths. Groups of newly manufactured albumen prints were repeatedly bathed in one of the four aqueous solutions, and changes in gloss were measured and compared. New print materials were produced for this study to provide some consistency in terms of fabrication and environmental history.
2.1 SAMPLE PREPARATION
Samples of unsensitized albumen-coated papers were obtained from the Image Permanence Institute (IPI) and the Chicago Albumen Works (CAW). Both fabricators coated the sheets by hand, using the same general procedures (Reilly 1980) and the same paper base (Munson 1996). The papers were coated in the late 1970s to early 1980s. Descriptions of their procedures are presented in appendix A.
Thirty-two samples of the albumenized paper, each approximately 5 by 8 in. (12.7 � 20.3 cm), were sensitized with silver nitrate, exposed, and processed in our laboratory (Reilly 1980; Munson 1996). The sensitized papers were printed out to maximum density without using negatives, as a dark surface was expected to make any cracks that formed easier to observe. Processing involved the following steps: wash, gold tone, wash, fix, wash, hypo clearing treatment, final wash, and drying. Details of the sensitizing, exposure, and processing procedures are described in appendix B.
After processing, it became apparent that there were three types of prints, distinguished by their average gloss and thickness. The prints from IPI tended to be thinner and less glossy than the ones from CAW.
- Type 1 (16 prints): thin (∼0.09 mm), low gloss (12 GU)
- Type 2 (8 prints): thick (∼0.10 mm), low gloss (12 GU)
- Type 3 (8 prints): thick (∼0.10 mm), high gloss (24 GU)
Because the two manufacturers used the same paper base and the same procedures to coat the sheets, the observed variations in initial gloss and thickness can be attributed to differences in the albumen viscosity and flow during application of the coating. Both manufacturers felt that variables inherent in the process such as temperature, relative humidity, age of egg, breed of chicken, and quality of the chicken life (free range or not) affected the final product. Both also stated that drying was important and that higher drying temperatures produced glossier emulsions. Aging of the solution can also be a factor. A 19th-century photographer working in Paris observed: “The older the albumen becomes, the more brilliant the coating will be, but there is some danger of yellowing of the proofs after the hyposulfite bath” (Ogonowski 1891, 17).
The focus of this study was to observe the relative effects of the treatment baths on a given set of available materials. As will be shown below, the relative effects of the baths were the same for all print types, so these variations in initial gloss and thickness, although interesting, did not affect the overall results of this study.
2.2 WET TREATMENTS
The 32 prints were divided into 4 treatment groups (A, B, C, D) of 8 samples each. Each group contained 4 prints from each fabricator. The print types based on initial gloss and thickness were also distributed equally among the treatment groups: each treatment group contained 4 prints with a thin albumen coating and a low initial gloss, 2 prints with a thick coating and a low initial gloss, and 2 prints with a thick coating and a high initial gloss. An identification mark was applied to each sample in pencil on the reverse. The samples were repeatedly subjected to the four wet treatments listed in table 1.
TABLE 1. WET TREATMENTS
Baths A, B, and C were chosen as examples of baths that may be used in the treatment of photographs. Bath D was chosen because it was thought there might be some benefit to replacing the water in the saturated prints with ethanol, causing the sample to dry more quickly while still retaining its enlarged dimension. A similar procedure is used in the preparation of biological samples for scanning electron microscopy/transmission electron microscopy (SEM/TEM) analysis (Harkins 1996). All solutions were used at room temperature.
2.3 DRYING TECHNIQUE
After each bath treatment, the samples were drained and blotted to remove standing water. The drying then proceeded under restraint, usually for five to seven days. The prints, with lens tissue against the recto and verso, were placed face down between layers of four-ply mat board, 3/8 in. (.95 cm) wool felt, and 1/2 in. (1.3 cm) Plexiglas. Once dry, the prints showed a strong tendency to curl, and so were kept flat in Mylar envelopes until the next treatment cycle. For the purposes of this study, it is only important that the drying technique was consistent throughout the project, as our objective was to study the effect of the treatment baths. The effects of different drying techniques will be the subject of a future study.
The wet-to-dry treatment cycles were repeated until obvious differences were seen when comparing the treatment groups. Messier and Vitale (1994; Vitale and Messier 1994), working with more fragile vintage albumen prints, observed significant changes after a single wet treatment, but this was not the case with the newly manufactured prints in this study. After 10 cycles, there were only slight differences among the groups. After 20 treatment cycles, clear differences among the groups had emerged, making it possible to compare the data and draw conclusions.
2.4 MEASUREMENT AND OBSERVATIONS
Changes in the surface of the prints were monitored by measuring the reduction in gloss. As roughness and cracking develop, the amount of scattered light increases and the gloss is reduced. The samples were measured with a Macbeth Novo-Gloss 20/60/85 Statistical glossmeter. This device measures gloss in incremental units of 0.1 GU (gloss units) and has a specified accuracy of 0.5 GU. The Novo-Gloss meter is capable of measuring gloss at 20�, 60� and 85� with respect to the surface normal (perpendicular to the plane of the sheet), and the selection of angle is determined by the smoothness of the surface being measured. For surfaces of low gloss, measurement at a larger angle will maximize the collection of the reflected light, thereby producing a more reliable result. The average thickness of the prints was measured with a Mitutoyo digital micrometer.
The gloss of the samples was recorded before the initial treatment bath and after every second treatment cycle. To reduce planar distortion, the samples were held flat on a paper suction table during measurement. The initial gloss of all the prints was relatively low, and therefore the surface was measured at both 60� and 85�. At 60�, the glossmeter measures an area approximately 2 cm2 in size, and this area increases to approximately 3 cm2 for measurements taken at 85�. Five spots were measured on each sheet, using a template as a guide to ensure that the same area was measured each time. The gloss was measured parallel to and across the grain (machine direction of the paper substrate) of the print at each spot. In all, 10 measurements were made at each angle after every second treatment cycle for each of the 32 samples in this study.
The data obtained at 60� and 85� exhibited similar trends, but the data obtained at 85� appeared to be more sensitive to smaller changes in gloss. For the sake of simplicity, only the data collected at 85� are presented here. As the bath treatments were repeated, the paper substrates showed increasing distortion, especially across the grain direction. As a result, gloss measurements taken perpendicular to the grain direction of the sheets exhibited a large degree of variation, while the measurements taken parallel to the grain showed a consistent decrease in gloss. For this reason, only the measurements taken parallel to the grain direction were used to assess the treatment results.
No cracks were apparent prior to the prints having been subjected to the treatment baths. During the course of the study, visual examination in normal, raking, and reflected light revealed that the prints appeared to become rougher and more matte. At the end of the study, cracks were clearly visible to the unaided eye, although not all prints exhibited the same degree of cracking. Stereo-microscopic examination (10 to 40x) and photomicrography were used to observe and record the relative quantities and size of the cracks that had developed as well as their preferred orientation, if any. At several locations on each print, the number of cracks in the field of view (at 40x) was estimated, and the results were averaged for the print. Similarly, the average length of the cracks was estimated.
Gloss was diminished in all of the samples in the study as a result of the aqueous treatments, and the amount of change in gloss was found to be related to the type of bath treatment. The average gloss change for all the samples in the study as a function of the number of immersions in each of the four treatment baths is presented in figure 1. The least reduction in gloss was observed for the samples treated with the water:ethanol (1:1 v:v) mixture (bath C). The water bath at pH 9 (bath B) and the water-only bath (bath A) resulted in only slightly more reduction than bath C. However, a significantly greater reduction in gloss was observed in the samples bathed in water followed immediately by ethanol (bath D).
The average decrease in gloss for all prints in the study as a function of the number of immersions in each of the four treatment baths. The water:ethanol mixture consistently showed the least reduction in gloss, while the bath of water followed by ethanol showed the greatest gloss reduction. The standard deviation of the values ranges from approximately 1 to 2 gloss units.
Although all three paper types exhibited the trend discussed above, differences in the magnitude of gloss reduction were observed among the print types. The average change in gloss after 20 treatment cycles produced by each treatment bath as a function of the initial gloss and thickness of each sheet is presented in figure 2. There appears to be a relationship between the thickness of the albumen coating and the change in gloss: samples with a thicker coating suffered a greater reduction in gloss than samples with a thinner coating. The figure also shows that the reduction in gloss does not appear to be related to the initial gloss of the print.
The average change in gloss over the course of the 20 treatment cycles for each of the three paper types in each of the four treatment baths. The bath of water followed by ethanol shows the greatest reduction in gloss, while the other three baths are quite similar, although the water:ethanol mixture does show slightly less gloss reduction. The thicker (∼0.10 mm) prints show a greater reduction in gloss than the thinner (∼0.09 mm) prints, regardless of the initial gloss.
Of the methods used, measuring with the glossmeter proved to be the most quantifiable method for recording changes in the surface of the samples. These changes included the development of cracks, but also roughening, minute dimpling, and other small deformations corresponding to the grain of the paper. Reduction in gloss most likely results from the stress imposed on the albumen layer during the wetting and drying cycles. The strain in the albumen layer is relieved by cracking and/or surface roughening, the degree of which depends on two factors: (1) the amount of stress imposed by the specific treatment, and (2) the differing responses of the albumen layer and the paper substrate.
Samples bathed in the water:ethanol mixture exhibited the least reduction in gloss. They were exposed to the smallest amount of water and, as a result, probably experienced the smallest degree of wet-to-dry expansion and contraction. Conversely, samples bathed in water followed by ethanol showed the greatest amount of gloss reduction and roughening of the surface. In this treatment, the samples expanded during the water bath and remained swollen as the water was displaced by ethanol. However, ethanol evaporates rapidly, causing dimensional changes that may have resulted in the observed increased gloss reduction. Furthermore, the displacement of water by ethanol may desiccate the emulsion, encouraging brittleness. The samples bathed in water and alkaline water showed an intermediate reduction in gloss. These samples may have expanded to a degree similar to those in the bath of water followed by ethanol but were not subjected to the rapid drying caused by immersion in ethanol.
The thicker samples consistently exhibited a greater reduction in gloss than those with thinner emulsions. Examination with the stereo-microscope at 40x provided general information about the number, size, and orientation of the cracks formed during this treatment study. In general, a greater number of cracks formed in the thicker samples than the thinner ones. Additionally, the cracks in the thicker samples were relatively long (>0.5 mm) and tended to form across the grain, while those in the thinner samples tended to be shorter (<0.1 mm) and showed no preferential direction. Similar observations have been reported by Alice Swan (1981, 275):
The severity of the fissuring and cleavage appears most directly related to the thickness of the albumen layer. The only albumen prints I have seen completely without fissuring are prints from the 1850s and 1860s, so thinly coated that they have almost no gloss and are sometimes mistaken for salt prints. Yet a more thickly coated spot on such a print will show the usual fissuring and cleavage, and the amount and severity will depend on the thickness of the spot.
These observations suggest that more stress may be assumed during treatment cycling by thicker layers of albumen than by thinner ones, which are better able to follow the expansion and contraction of the paper substrate.
If aqueous treatment of an albumen print is necessary, it is important to reduce stress on the albumen-paper laminate. Limiting the expansion of albumen prints during aqueous treatments through the use of water and ethanol mixtures appears to be beneficial. Along the same lines, prints should be dried slowly, making the transition from wet to dry as gradual as possible to avoid abrupt dimensional changes. This study indicated that bathing samples in water ammoniated to pH 9 caused slightly less cracking than water alone. It is known among photograph conservators that ammoniated water causes greater swelling of proteinaceous emulsions than water alone. The elevated pH may make the albumen layer more elastic, allowing it to move more easily with the reactive paper substrate. Ammonia, however, may adversely affect silver compounds (Haist 1979, 248) and therefore should be used with caution until its effects are better understood.
The results of this study have shown that by using a mixture of water and ethanol and carefully controlling the wetting and drying conditions, it may be possible to moderate the effects of aqueous treatments on albumen prints. A comparison of the effects of different drying methods will be the subject of a future study.
The authors are indebted to the following individuals for their invaluable assistance and insights: Charles Harkins, Wayne State University Biology Department; Douglas Munson, Chicago Albumen Works; Douglas Nishimura, Image Permanence Institute; Steve Puglia, National Archives and Records Administration; James Reilly, Image Permanence Institute; Doug Severson, Art Institute of Chicago; Leon Stodulski, Detroit Institute of Arts; and Sara Wagner, National Archives and Records Administration.
. An abbreviated version of this paper was presented at the AIC Photographic Materials Group Winter Meeting, San Francisco, 1997, and published in Topics in Photographic Preservation, vol. 7 (Washington, D.C.: American Institute for Conservation Photographic Materials Group, 1997). The present article incorporates several additions and revisions.
1.1 A: MANUFACTURING PROCEDURES FOR ALBUMEN-COATED PAPER
Following are descriptions of the procedures used to produce the sample papers for the project. As stated in the text, the manufacturers used similar methods and the same paper base. The samples used in our study were made in the late 1970s/early 1980s, and these recipes are reconstructions of what was most likely done at that time.
A 60 gsm 100% rag photo base paper produced in a special run by the Simpson-Lee Paper Co. of Kalamazoo (now defunct). This lot was shared by Image Permanence Institute (IPI) and Chicago Albumen Works (CAW).
- IPI (paraphrased from Reilly, 1980, 36–40)Beat for 3 minutes, or until the entire mixture has been converted to a froth. Let settle for 24 hours, strain through muslin, and store covered in the refrigerator for one week. Allow to come to room temperature before using. Just prior to coating, gently stir in 4 ml of Kodak Photo-flodiluted 1:200 with water. If double coating is desired, hardening between coats can be achieved by warm aging for six months, steam, or a 70% isopropyl alcohol bath.
- CAW (Munson 1998)Douglas Munson stated that the methods used varied considerably from time to time. His comments on the procedures he used are paraphrased here:
Combine:6 gal. (approximately 23 liters)fresh egg whites0.5 to 3% ammonium chlorideWhip to a soft meringue. Allow to settle, strain, and just before coating, add Kodak Photo-flo, about 1:1000. The solution was not deliberately aged or fermented, but the coatings were done either immediately or shortly after processing the albumen. The sheets of paper were single, double, or triple coated and were sometimes hardened.
1.2 B: PHOTOSENSITIZING, EXPOSURE, AND PROCESSING PROCEDURES
- Spray sheets lightly with water on both sides to dampen them.
- Float sheets, albumen side down, on 12% silver nitrate (AgNO3) solution for 2 1/2 to 3 minutes (under red safelight).
- Hang sheets by corner to dry (safelight).
- While still damp, expose prints to daylight without negatives under Mylar on a Fome Cor support, for approximately 20 minutes, producing completely printed out sheets.
- Initial wash: Wash prints in running water for 10 minutes to remove excess silver nitrate.
- Gold toning: Prepare toning solution: 10g borax (Na2B4O7�10H2O), and 0.5g gold chloride as tetrachloroauric (III) acid (HAuCl4), diluted with deionized water to make 1 liter. Immerse prints in toning solution for 3 minutes.
- Wash: Wash prints in running water for 5 minutes.
- Fixing: Prepare fixing solution: 150g sodium thiosulfate pentahydrate (Na2S2O3�5H2O) and 2g sodium carbonate (Na2CO3) diluted with deionized water to make 1 liter. Divide into two baths, and immerse prints in each bath for 5 minutes.
- Wash: Wash prints for 2 to 4 minutes in running water.
- Hypo clearing bath: Prepare hypo clearing agent: 10g sodium sulfite (Na2SO3) in deionized water to make 1 liter. Immerse prints in bath for 3 to 5 minutes to remove thiosulfate.
- Final wash: Wash prints for a minimum of 30 minutes in running water.
- Drying: Air-dry without restraint.
ALBUMEN MATERIALS LIST
Harkins, C.1996. Personal communication. Biology Department, Wayne State University, Detroit, Mich. 48202
Haist, G.1979. Modern photographic processing. New York: John Wiley and Sons.
McCormick-Goodhart, M., and M.Mecklenburg1992. Cold storage environments for photographic materials. AIC abstracts, American Institute for Conservation 20th Annual Meeting, Buffalo, N.Y. Washington, D.C.: AIC. 55–56.
Messier, P., and T.Vitale. 1994. Effects of aqueous treatments on albumen photographs. Journal of the American Institute for Conservation33:257–78.
Munson, D.1996. Personal communication. Chicago Albumen Works, P.O. Box 805, Housatonic, Mass. 01236.
Munson, D.1998. Personal communication. Chicago Albumen Works, P.O. Box 805, Housatonic, Mass. 01236.
Ogonowski, E.1891. La photochromie: Tirage d'epreuves photographiques en couleur. Paris: Gauthier-Villars et fils.
Reilly, J.1980. The albumen and salted paper book: The history and practice of photographic printingm, 1840–1895. Rochester, N.Y.: Light Impressions Corporation.
Swan, A.1981. Conservation of photographic print collections. Library Trends30:267–96.
Vitale, T., and P.Messier. 1994. Physical and mechanical properties of albumen photographs. Journal of the American Institute for Conservation33:279–99.
Bergquist, D. H.1986. Egg dehydration. In Egg science and technology. 3d ed.Westport, Conn.: AVI Publishing Co.285–323.
Calhoun, J., and A.Leister. 1959. Effect of gelatin layers on the dimensional stability of photographic film. Photographic Science and Engineering3:8–17.
Karpowicz, A.1989. In-plane deformations of films of size on paintings in the glass transition region. Studies in Conservation34:67–74.
Kuntz, I., and W.Kauzmann. 1974. Hydration of proteins and polypeptides. In Advances in protein chemistry, vol. 28, ed.C. D.Anfinsen et al. New York: Academic Press. 239–345.
Mecklenburg, M. F., M.McCormick-Goodhart, and C. S.Tumosa, 1994. Investigation into the deterioration of paintings and photographs using computerized modeling of stress development. Journal of the American Institute for Conservation33:153–70.
Messier, P.1991a. Protein chemistry of albumen photographs. In Topics in photographic preservation, vol. 4. Washington D.C.: American Institute for Conservation Photographic Materials Group. 124–35.
Messier, P.1991b. Work in progress: An analysis of the effects of water on the cracking of albumen photographs. In Topics in photographic preservation, vol. 4. Washington D.C.: American Institute for Conservation Photographic Materials Group. 170–78.
Powrie, W., and S.Nakai. 1986. The chemistry of eggs and egg products. In Egg science and technology. 3d ed.Westport, Conn.: AVI Publishing Co.97–139.
Reilly, J.1982. Image deterioration in albumen photographic prints. Preprints of the 9th International Congress of the IIC, Washington, D.C. London: International Institute for Conservation. 61–65.
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SOURCES OF MATERIALSAlbumenized papers (not currently commercially available)
Chicago Albumen Works, P.O. Box 805, Housatonic, Mass. 01236
Image Permanence Institute, Rochester Institute of Technology, 70 Lomb Memorial Dr. Rochester, N.Y. 14623Glossmeter
MacBeth, a division of Kollmorgen Instruments Corporation, 405 Little Britain Rd. New Windsor, N.Y. 12553-6148Micrometer
Mitutoyo Corporation, 31-19. Shiba5-chome. Minato-ku, Tokyo 108, JapanSilver nitrate, sodium thiosulfate, sodium carbonate
Fisher Scientific Company, 2000 Park Lane Dr. Pittsburgh, Pa. 15275-9952Gold chloride (tetrachloroauric (III) acid)
Sigma Chemical Company, P.O. Box 14508, St. Louis, Mo. 63178Sodium sulfite
Mallinckrodt Laboratory Chemicals, 222 Red School Lane, Phillipsburg, N.J. 08865Borax (20 Mule Team Borax)
Dial Corporation, Consumer Products Division, Phoenix, Ariz. 85077Green's Lens Tissue
Rising Museum Mounting Board (four-ply, warm white), Talas, 568 Broadway, New York, N.Y. 10012
VALERIE BAAS received an M.F.A. in print-making from Michigan State University in 1976 and an M.S. in conservation at the Winter-thur/University of Delaware Art Conservation Program in 1980. She has been the head of the paper and photographs section of the Conservation Services Laboratory at the Detroit Institute of Arts since 1980. Address: The Detroit Institute of Arts, Conservation Services Laboratory, 5200 Woodward Ave., Detroit, Mich. 48202.
CHRISTOPHER FOSTER received an M.S. in conservation from the Winterthur/University of Delaware Art Conservation Program in 1987. In 1988 he began work at the Yale Center for British Art and Yale University Art Gallery, as assistant paper conservator. He has been the associate conservator of art on paper and photographs at the Detroit Institute of Arts Conservation Services Laboratory since 1994. Address as for Baas.
KAREN TRENTELMAN received a Ph.D. in physical chemistry from Cornell University in 1989. She is presently associate research scientist in the Conservation Services Laboratory at the Detroit Institute of Arts. She joined the DIA in 1995 following an appointment as assistant professor of conservation science in the Art Conservation Department at the State University of New York at Buffalo. Address as for Baas.