Ultraviolet-induced visible fluorescence and chemical analysis as tools for examining featherwork

Ellen Pearlstein, Melissa Hughs, Joy Mazurek, Kevin McGraw, Christel Pesme, Renée Riedler and Molly Gleeson

Abstract

Feathers are found in cultural heritage collections of tribal arts from the Americas, Africa, and the Pacific as well as in contemporary art, European and American fashion, and in taxidermy and ornithology specimens. Although museum conservators routinely evaluate feathers by looking at insect damage and mechanical wear, as well as fading as evidence of light exposure, examination of feathers for visible fluorescence under an ultraviolet (UV) source is atypical. Recent research by both the authors and bird biologists indicate that nondestructive UV fluorescence examination can provide valuable information about the identification and pigmentation of feathers found in museum collections, but must be used with caution as both light exposure and adventitious materials may compromise fluorescence. The authors also evaluate different methods of chemical analysis for detecting light-induced chemical changes in feathers.

Recent research conducted jointly by UCLA and the Getty Conservation Institute illustrated the importance of identifying feather pigmentation systems in the design of a preventive conservation strategy. The difference in the quantity of light needed to fade undyed feathers can be 10-fold depending on the colorant systems present in the feather and the emission spectrum of the light. Feathers with color derived from the scattering of light through small scale feather structures are known to be more light-stable than feathers with coloration based on biological pigments. A number of feather pigments, including psittacofulvins found only in red and yellow pigments in birds in the Psittaciforme family, as well as porphyrins found in rusty brown owl plumage, may be identified by their specific ultraviolet-induced visible fluorescence (UVIVF).

Feathers whose pigments are not directly fluorescent may still undergo appearance changes under an UV source as a consequence of light aging. Fluorescence is an early marker of chemical change, and can be used to detect such change before it can be measured colorimetrically. Beyond knowing that UV fluorescence is a stable attribute of some feather pigments, and a light-sensitive attribute in others, the current authors were motivated to determine whether color shifts visible in UV-induced fluorescence could provide a nondestructive marker of photochemical change to the keratin feather structure. This article describes a variety of analytical techniques applied to light-aged feather samples to present the most sensitive methods for detecting chemical changes that parallel fluorescence changes. Museum feather work, some with records of estimated display, were examined using UVIVF both to document psittacofulvin pigmented feathers expected to display fluorescence, and to compare non-psittacofulvin-pigmented feathers with accelerated-aged feather samples.

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