INVESTIGATION OF A SURFACE TARNISH FOUND ON 19TH-CENTURY DAGUERREOTYPES
LEE ANN DAFFNER, DAN KUSHEL, & JOHN M. MESSINGER
Short-wave ultraviolet examination yields a uniquely discernible fluorescence pattern on some daguerreotype plates. The origin of this fluorescence has not been established conclusively, nor has the stability of the fluorescing material. Nevertheless, short-wave ultraviolet documentation can be part of active monitoring programs for daguerreotypes. Documentation of this fluorescence may prove to be an extremely useful method for indicating the progression of tarnishing patterns.
The carbon-nitrogen triple bond bands present in the FTIR spectra are associated with different salts. Identification of the various fluorescence patterns may provide evidence of the technical history of individual plates. As described above, there are at least six ways in which cyanide could have been introduced into the daguerreotype process.
The procedure of examining daguerreotypes under short-wave ultraviolet radiation requires special safety considerations during handling for both the object and the examiner. When unbound, the delicate daguerreotype plate is extremely vulnerable to surface abrasion. The photographing of bare, unprotected plates should be conducted only by an experienced photographer, preferably in the presence of a conservator. During examination, extreme caution should be used when handling bare plates that have shown fluorescence due to the highly toxic nature of cuprous cyanide and silver cyanide. While areas of copper cyanide compounds may be identified by fluorescence, silver cyanide is a grayish white to black powder that could easily go undetected on the multifaceted terrain of the daguerreotype surface. Safety precautions should be undertaken, such as wearing ultraviolet-absorbing safety glasses to protect the eyes and latex examination gloves to prevent contact with cyanide. Inhalation of surface debris should be avoided at all costs, as the cyanide compounds are fast acting, deadly poisons (Strahan 1980).
It was noted that the plates examined that had remained adequately sealed did not show significant development of the tarnish. Therefore opening the plate package is not recommended unless the seals are inadequate and need to be replaced or a thorough, systematic monitoring project is to be undertaken for the entire collection.
The complex nature of the daguerreotype has yet to be fully understood. Little by little, we are gaining insight to its structure and deterioration to aid in its preservation and appreciation. Interpretation of the fluorescence observed on daguerreotype plates deserves further attention and research, and we hope this investigation will inspire other conservators and scientists to explore this phenomenon.
The SEM studies were carried out by Peter Bush, director, Biomaterial Instrument Center, State University College at Buffalo. The FTIR spectra were obtained by Sharon Markel of the Eastman Kodak Analytical Technology Department, Eastman Kodak Company, Rochester. We are grateful to both for having given many hours of their time to this project. The authors would like to thank the Strong Museum and conservation staff at the George Eastman House for the use of their facilities. We are grateful to Grant Romer, director of museum practices and conservation at the George Eastman House, for first suggesting the use of long-wave ultraviolet radiation for examining daguerreotypes and for his assistance in this study. We would also like to thank F. Christopher Tahk, director of the Art Conservation Department of the State University College at Buffalo, for expert guidance and the use of his daguerreotype collection.