Vincent Beltran from the Getty Conservation Institute presented this talk in the Research and Technical Studies session. The study presented examined the effects of anoxia and hypoxia on light-induced color change in a sample set containing a variety of materials. The goal was to examine the use of these environments in storage and exhibits as part of an effort to improve the experience for visitors viewing light-sensitive items.
The talk was organized into four parts: “Introduction,” “Experimental Method,” “Microfader Results,” and “Comparison to Lightbox Study.”
In the introduction, Beltran reviewed traditional practices to mitigate the damaging qualities of light. For example: reduce light levels, limit exposure time, rotate exhibit items, and store items in the dark. He then provided an overview of the photo-oxidation process, and the theories behind the use of anoxic and hypoxic environments for storage.
A 2012 study of 125 colorants exposed in a halogen lightbox for 17.5 MLux hours at 22° C, 40% RH with oxygen levels at <10 ppm indicated that 90% of these items studied showed reduced color change as compared to the same items stored in air. To the authors, the logical extension of this study was to transfer the test to the microfading tester and compare the results.
The design of the lightbox for the microfading tester study involved a xenon light projecting through ¼” starfire glass to items on a sample stand. Light was reflected to a spectrometer located above the glass. A ½ cm gap existed between the samples and the glass. The microfader was located above the case while the colorants were inside the case. The colorants consisted of 3 blue wool, 4 organic dyes, 2 leaves, 1 grass, 5 gouaches, 1 watercolor with prussian blue, 1 Kremer Prussian Blue, and 1 Crystal Violet. The colorants were exposed for 5 MLux hours in air, anoxia (<200 ppm oxygen), and hypoxia (1% and 5% oxygen). Reflectance spectra were obtained and combined for a color change plot.
The results of the microfading tester study showed that for the most part color change in air is higher than that in anoxia. Anoxic environments seemed to be generally equivalent to the 1% oxygen environments. A few colorants exhibited a slightly decreased change in the 1% environment but Beltran indicated that these results were inconclusive. A few exhibited increased change in the 1%. Environments with 5% oxygen tended to exhibit more change than anoxic or 1% but generally not as much change as found in air. The exception to this is Prussian blue, which shows the opposite behavior – an air environment showed the least change, 5% followed, and 1% and anoxic showed the most change. Overall, the results showed that 12 of the 18 colorants exhibited greater change in air while only one (Prussian blue) exhibited the greatest change in anoxia. Generally, hypoxic environments exhibited less change than air.
Beltran then presented a comparison between the 2012 study and the more recent microfader study. The main differences in the studies were as follows:
Study Component: Microfader Lightbox
Light Source: Xenon Halogen
Exposure level: 5 MLux 0.01 MLux
Exposure time: 3.5 hours 1750 hours
Exposure type: Continuous Start/End
Area exposed: 4 mm spot Broad exposure
In general, the color change with the lightbox test was higher than that seen with the microfader, though some samples showed changes which were roughly equivalent. Most items showed similar behavior between the two techniques but the lightbox displayed increased change. The differences in the studies were typically within one blue wool step, and the study was able to consistently classify relative color change between the two techniques. However, Beltran stated that there is reciprocity failure between the two studies.
Future goals of this project are to repeat the analysis with more samples, examine the effect on reciprocity for the microfading tester at reduced light intensity, and study the color change in various RH and temperature levels.
Questions were as follows:
Q: In cases where the microfading tester and lightbox didn’t agree, is the lightbox the more reliable?
A: In general, lower light exposure tends to be closer to what you’d get with the microfading tester but that doesn’t mean reciprocity is holding.
Q: Has the microfading tester been tried with a halogen bulb?
A: No, they tried to modify a halogen source but it didn’t do much.
Q: Were control samples used?
A: No, they were not..