1 INTRODUCTION

The introduction of fluorescent colorants constitutes a significant advance in 20th-century color technology. Originally developed for use in applications where high visibility was required, such as coloration of road construction markers or search and rescue vehicles, they were eventually used to develop a variety of fluorescent artist's materials. With these new materials came a new set of conservation concerns. Fluorescent colorants have been observed to degrade rapidly when exposed to light, particularly during prolonged exposure (Voedisch 1973). Preservation measures typically employed when exhibiting fugitive materials—restricting the wavelength region of the illuminating light source and decreasing the intensity of illumination—may impact fluorescent colorants by changing their luminous appearance, dependent as it is on both reflected light and fluorescent emission. Thus appearance changes that occur in fluorescent colorants can be difficult to anticipate or to match during conservation treatments such as inpainting.

The goal of this study is to provide a better understanding of fluorescent materials and their fading behavior so that museum professionals may be better able to make exhibition and conservation decisions. Currently, a wide variety of fluorescent art materials is available, including pigments, dyes, inks, and watercolors. However, only a small number of fluorescent dyes (most commonly, CI Basic Violet 10, CI Basic Red 1, CI Acid Yellow 73, CI Solvent Yellow 44, CI Acid Yellow 7, CI Disperse Yellow 232, CI Basic Yellow 40, and CI Disperse Yellow 11) are used to create these art materials (Smith 1982; Christie 1993). In this study, 12 fluorescent watercolors from the Dr. Ph. Martin Radiant Concentrated Water Color line of products (Fuchsia, Raspberry, Sunrise Pink, Tahiti Red, Ice Pink, Tropic Pink, Ice Yellow, Tropic Gold, Sunset Orange, Sunset Red, Ice Green, and Sunshine Yellow) were chosen as examples of fluorescent materials used by both commercial and fine artists and likely to contain the typical fluorescent dyes mentioned above. The appearance changes of these watercolors under various lighting conditions (high and low correlated-color-temperature [CCT] sources, simulated daylight sources with ultraviolet wavelengths both included and excluded, and a black light source)1 and from prolonged exposure to these lighting conditions were explored along with the preservation benefits gained from the exclusion of UV wavelengths from a simulated daylight source. Consideration is also given to the conservation issues that surround fluorescent materials, specifically the attempt to match the fluorescent color on an artwork during treatment and to infer the original appearance.