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Visible effects of adhesive and pressure on color in kingfisher feathers


Structurally colored feathers render color through physical scattering of light rather than pigments. There is an expected, but heretofore unexplored, effect of adhesive choice and pressure on the color of these materials. Further, such feathers are generally considered to be more light-stable than their pigmented counterparts. In the current study, structurally colored blue kingfisher feathers are used to examine these effects in order to guide conservation treatments and preventive care.

The Chinese tradition of diancui, literally "dotting [a surface] with [kingfisher-feather] blue", describes a technique of cloisonné style jewelry that utilizes blue, blue-green, and purple feathers instead of fused glass powder. The feathers are adhered to a substrate, usually metallic, though occasionally composed of thick layers of paper. This technique appears in Chinese culture from as early as the first century BCE, though surviving examples date most prevalently to the Qing dynasty (19th century) (Chambers et al. 1981, 32). The early featherwork items were not restricted to jewelry, but also appeared in the form of feather mosaics on clothing, bed coverings, and palanquins (Chambers et al. 1981, 32; Garrett 1994, 86). Such items are now ubiquitous in museum collections. Through a technical study of kingfisher feather jewelry from the Ruth Chandler Williamson Gallery at Scripps College in Claremont California, as well as accelerated light aging studies and pressure tests completed on mocked up samples of recently plucked kingfisher feathers at both the UCLA/Getty and the Getty Conservation Institute labs, I evaluate the effects of original and conservation/restoration adhesives and coatings, and effects of mechanical interactions, on the structural colors of the feathers.

For the experimental part of the study, feather specimens from skins of Halcyon smyrnensis, the White-breasted Kingfisher, donated by the United States Fish and Wildlife Department, were plucked, trimmed, and adhered onto inert quartz glass plates and subjected to three methods of light aging, with color measurements occurring after aging with an integrating sphere. The accelerated light aging methods included museum conditions (free of ultraviolet radiation), window conditions (ultraviolet radiation present), and high intensity UVA conditions, with an additional control group kept in the dark. Adhesive systems tested were those documented as having been used originally or in the conservation of kingfisher featherwork, including: protein glues (gelatin and isinglass), funori, methylcellulose, and Paraloid B-72. Characterizing the adhesives used on the Scripps collection items provided supporting technical evidence.

Taken together, the results of this study provide insights into kingfisher feather diancui technology, and the effect of adhesive systems and mechanical actions on the preservation of color within these structurally colored feathers. The color stability is strong, with little visible alteration in the color of unadhered feather samples from all aging chambers. However, feathers subjected to high intensity UVA radiation displayed the most significant shift in a* and b* values, becoming more colorless or grey. Adhesive choice does not result in a major difference in feather color, except Paraloid B-72, which results in darker, more saturated blue-greens. The yellow-green spots apparent on the kingfisher jewelry were not recreated on the mocked up samples and require further investigation. As the likely source for original adhesives, animal glue (or gelatin), isinglass, and funori are not recommended for conservation intervention. Methylcellulose, of the tested adhesives, may be the best choice for stabilizing comparative objects.

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