pigmented colorants: dependence on media and time - Cornell ...

pressure changes, or other atmospheric effects.
Some pigments darken, as seen with Vermillion (the red form of mercuric sul-
fide) in Figure 4.15. In the unexposed sample, Vermillion’s characteristic red ap-
pearance is dictated by the high reflectance in the long-wavelength range of the
visible spectrum. As the sample is exposed to an Atlas xenon arc Fade-Ometer, one
readily notices that the reflectance maxima in the long wavelength region decreases
with age due to the darkening.
Figure 4.15: Reflectance of Vermillion before and after exposure in the
Fade-Ometer. Adapted from [JF01].
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For extra protection from these effects, museum curators sometimes install glass