The amount of research investigating the risks of light damage to fine art materials is very small, but the amount directed at ethnographic and natural history materials is even smaller. More might have been done if the fundamental properties of many of these products were easier to characterize.

Ethnographic Materials with Biocolorants and Structural Colors

Unlike paints and dyes, biological colors are divided into those created by biopigments and those produced by a handful of physical phenomena that constructively and/or destructively interfere with reflected light. Structural colors are notoriously difficult to measure in a repeatable manner. Iridescence, for example, causes an angular dependence to color that gives butterfly wings and peacock feathers their enormous range of appearance effect.

It was not until recently that the main parameters that specify and define the geometry of color measurement –the angle between illumination and observation axes (Θ), the angle between the measured surface plane and the illumination/observation plane (Φ), and the orientation of the surface in regard to the axis around which the sample surface can rotate(ω) – were introduced systematically into feather color measurement.

One technique that has been exploited by biologists to measure the color of birds employs the bidirectional reflectance distribution function (BRDF). In this technique, overall color appearance can be described by a series of incident and reflected light beams with small solid angles. Measurement of BRDF at different incident wavelengths is thus exceedingly burdensome and to gain realistic experimental insights into light damage the approach needs to be simplified.

In a feather, this can be achieved using a limited multi-angle series of incident and reflectance measurements, but since the organization of feather structure also includes large macro-scale features (e.g., feather barbs and barbules), rotational freedom about those features also need to be incorporated into any function.

It becomes an important decision which subset of solid angles and barbule orientations imbed the best discrimination between structural and biopigment changes when estimating overall light sensitivity. This question has never been resolved in conservation research and is part of the project’s goals. The current recommendations on feather ISO blue wool sensitivities are, at best, conjectural. Some of the literature even permits a skewed interpretation based upon a few uniquely sensitive members of the superset of feather colorant systems that are possibly atypical and unique.

The overall goal was to better identify the light-sensitivity of anthropological, fine art, and natural history artifacts composed in part, or totally, of feathers.