Protective Effects of Anoxic Enclosures

Previous studies have suggested that while many light-sensitive pigments and dyes will benefit from being displayed in an oxygen-free environment, some pigments and dyes will change via photo-reductive processes or show no differences whatsoever. These earlier studies were based on a limited set of materials. Some studies also used oxygen scavengers, which might not have attained low enough oxygen concentration to produce meaningful results, or did not report oxygen concentrations to which samples were exposed, making comparison to current results difficult. In these earlier studies, temperature and relative humidity were seldom controlled to the extent they would be in museum display conditions. Thus, as important as this work is, the full magnitude of the photo-reductive extent on colorants cannot be estimated. Recent work by Lerwill (2012) filled in many of these gaps but has likewise created more questions concerning anoxic benefits.

Anoxic Enclosures at the GCI

This area of research applies nearly 15 years of Getty experience in designing and building environmentally-controlled, oxygen-free display cases, to photochemical damage research. The initial experiment consisted of a pair of matched display cases, one with a normal atmosphere and one with a nitrogen atmosphere, irradiated under banks of MR-16 lamps. Temperature control was achieved with a recirculating, liquid-cooled, closed loop system, which in turn allows for stable relative humidity conditions, and oxygen concentration was measured in the anoxic environment.

By the end of 2007, the first sample set had been exposed and their color changes measured. This set of samples consisted largely of pigments from the Edward Waldo Forbes collection and the GCI Reference Collection, augmented by a set of experimental lake pigments provided by the Library of Congress and plant materials provided by Rob Waller at the Canadian Museum of Nature.
A second set of materials was exposed and assessed for color change during spring 2008 and included a large set of historic dyes on natural fiber made by Cecily Grzywacz, former GCI scientist (currently at the National Gallery of Art), and Jan Wouters, formerly of Royal Institute for Cultural Heritage, Belgium, for the GCI's Asian Organic Colorants project. In addition, several sets of commercial materials were exposed, including Windsor and Newton gouache paints and Dr. Ph. Martin's watercolors (aniline-based dyes).

Results from both trials indicated that the vast majority of samples (90% of sample set) demonstrated a clear benefit from oxygen-free light exposure. Among this subset, 39% displayed color change in anoxia between two and four times lower than that observed in air, whereas 47% showed color change in anoxia reduced by a factor of four or more. In contrast, six samples exhibited greater color change in oxygen-free environments than in air these samples included Prussian blue watercolor (three samples), Antwerp blue watercolor, Verdigris dry pigment, and Fluorescent Yellow Winsor & Newton Gouache.
Results from the first trial were discussed at the 2008 ICOM-CC Triennial Meeting in New Delhi, India, with presentation of the second exposure results at the AIC Annual Meeting in Los Angeles in 2009. The combined results were published in 2012 in Studies in Conservation. In addition, CIELAB (Commission Internationale de lEclairage 1976 L*, a*, b*) coordinates (pre- and post-exposure) and E data (1976, 1994, and 2000 calculations) for all colorants discussed in the Studies in Conservation article are available as a supplementary table.

Future work will build on this earlier research by combining the environmental control and monitoring provided by the existing exposure case setup with microfading. The preliminary protocol is to duplicate the exposures of the initial experiment but substitute microfading through the glass-top of the display cases in both air and nitrogen environments. This technique confers the benefits of reduced exposure times due to its high-intensity xenon light source and simultaneous and continuous color measurement, and has been previously used by Hoyo-Melendez & Mecklenburg (2011b) and Lerwill to assess anoxic color change. These experiments will compare the ability of the microfader to derive data similar to that generated by more conventional lightbox aging.