4 DISCUSSION AND CONCLUSIONS

The results of the survey provide an objective basis for the widely held observation that the use of optical brightening agents in photographic paper began in the early to mid-1950s and increased rapidly thereafter. The survey also gives some insight into the extent of brightener use by the various manufacturers over time, making a strong case that a very large proportion, and in some cases the majority, of fiber-based, gelatin silver papers contained optical brightening agents for certain periods during the 20th century. As the reference collection continues to grow, new additions to the collection will be checked for optical brighteners, and these data will be periodically added to the results presented in this study.

This work highlights some important issues for the characterization of photographic papers. In particular, the method used to determine whether a paper contained optical brightening agents has limitations. While visual inspection in the dark with near-ultraviolet radiation is generally fine for detecting most occurrences of optical brighteners, there is a subjective component to this method that can be problematic in some cases. Many photographic papers appear “bright” observed with ultraviolet radiation but are not necessarily “brightened.” A bright appearance can be attributed to other factors besides optical brightening agents. For instance, gelatin has a natural fluorescence that can be enhanced through the use of certain dyes or other additives (Wentzel 1960). Baryta coatings also can be highly reflective of unfiltered blue light emitted by most sources of near-ultraviolet radiation. This blue reflection can sometimes be difficult to distinguish from the blue-white fluorescence emitted by optical brightening agents. These complicating factors are easily overcome when prints have a high concentration of functional optical brightening agents, as shown in figure 6. However, these and other variables can present a more significant problem if the brighteners are degraded or present in low concentrations. While it is extremely unlikely that these complications had a significant influence on the overall results presented in this study (as mentioned in sec. 2.3, samples with uncertain brightener content amounted to no more than 10 or 12 samples, or less than 0.6% of the entire sample group), experience examining historic photographs that have been displayed (unlike the samples used in this study) or stored under adverse conditions

Fig. 6.

Fluorescence of photographic paper exposed to near-ultraviolet radiation. From left to right the samples are: (a), Kodak Opal G, expiration date 1962, which contains no optical brightening agents; (b), the same paper showing contamination with brighteners, compared to (c), a sample of brightened paper, Agfa Brovira 117, from the early 1960s.

The research also indicated that brighteners, at least for some samples, are water-soluble. Many samples prepared early in the project were washed together. Upon inspection with ultraviolet radiation it became clear that some samples were picking up brighteners from immersion with other samples and/or from contact with wet samples. This observation has been made by others (Lav�drine 1995) and bears additional research. Water solubility of brighteners could affect conservation treatment practice, especially for wet treatments applied to optically brightened photographs or for treatments during which optically brightened and unbrightened photographs might be intermingled. For this project, contaminated and suspect samples were resampled, washed, and dried individually. As shown in figure 6, contaminated samples were generally easy to detect, as the brighteners were present in discrete patches or blurry spots and swirls.

It is likely that more fiber-based, black-and-white papers made after the mid-1950s contain brighteners than are indicated by the results of this study. Processing chemistry, such as developers and postprocessing treatments, can also add brighteners to photographic paper. The availability and prevalence of such treatments over the past 50 years need closer examination.

Due to the large proportion of 20th-century prints found to contain optical brightening agents and since there is a chance that wet treatment can affect brighteners, some changes in conventional conservation practice might be worth consideration. The first step in this process would be to document the presence of brightening agents as a matter of course before and after conservation treatment. Ideally an approach based on shared reference standards could be developed so that documentation obtained by one conservator could be objectively compared with the work of another. More research is needed to determine the susceptibility of optical brighteners to being damaged from exposure both to near-ultraviolet radiation and to light. Along these lines, investigation is needed to determine whether degraded brighteners can actually produce undesirable visual effects such as highlight yellowing. Results of this research may have a significant impact on recommended light levels and display durations for gelatin silver developing out prints.

The apparent drop in the use of optical brightening agents for fiber-based papers noted in the period 1965 to 1979 was an unexpected and interesting finding. A possible explanation for this decline is the fact that this period coincides with a major industrywide shift toward the production of resin-coated (RC) papers. Made with a bright white base of titanium dioxide–pigmented polyethylene, these papers had quicker processing times and improved dimensional stability as compared to fiber-based papers. These attributes formed the basis of a marketing strategy aimed at high-volume professional applications in which increased productivity held great appeal. The introduction of resin-coated paper also occurred during a time when fine art photographers, such as Ansel Adams and Minor White, were paying increased attention to print quality and materials. Adams wrote that he did “not personally favor the image quality of RC papers” (Adams 1983, 43). Given this context, it seems possible that paper manufacturers responded to photographers who sought to contrast commercial applications with fine art printmaking by offering a greater range of fiber-based papers without optical brightening agents.

As the incorporation of optical brighteners is an intrinsic quality that affects the visual appearance of a photograph, some consideration should be given to what, if any, aesthetic attributes are being sacrificed during the display of prints with the brighteners “switched off” (under conditions of low or no ultraviolet radiation). However, before embarking on widespread display of photographs with brighteners “switched on,” more research will be needed to determine the peak excitation wavelengths and minimal intensities for the activation of optical brightening agents. Given the poor stability generally associated with optical brightening agents, it is unclear whether conservators, curators, and collectors will gradually place relatively higher values on prints that have intact brighteners and thus can conceivably be “displayed as intended” by the photographer. If so, additional work will be needed to determine the dark storage aging properties of brighteners and whether specialized storage environments, such as cold storage, are effective in preserving brighteners. Considering the widespread use of brighteners documented in this study, it is a difficult but realistic conclusion that a large proportion of gelatin silver prints are most likely not as stable as widely believed, at least from the standpoint of visual attributes governed by optical brightening agents.

ACKNOWLEDGEMENTS

The authors wish to thank Martin Hadwen, Motor Racing Archive and Research, Watton, Thetford, Norfolk, England; Mark Patrick, director of the National Automotive History Collection, Detroit Public Library; Karl Ludvigsen, Ludvigsen Library, Hawkedon, Bury St. Edmunds, Suffolk, England; Karen Middleton, assistant professor of fashion design, Fashion Institute of Technology, New York; and Dr. Janos Wimpffen, Motorsport Research Group, Redmond, Washington, for their expertise in dating samples based on image content (particularly cars and fashion design). Mark Messier, assistant professor of physics, Indiana University, Bloomington, provided tremendously useful advice for the presentation and analysis of the data presented in this paper.