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

over time. Perceptually, these hues have much greater differences than the darker
ones, as seen by the magnitude of the distances between points. Typically, it is
this last type of change that we recognize as fading. That darker colors actually
increase in chroma, or saturation, thus appearing to get brighter as they get lighter,
is not often understood to be the result of fading.
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Figure 4.18: Fading of the five Alizarin Crimson hues used in Figure 4.17
in respect to Munsell value and chroma. As the samples age, the exposed
samples (black dots) tend to shift from their original appearance
(white dots). Adapted from [JF01].
A consequence of this drastic loss of <strong>pigmented</strong> colorant is that the resulting
artwork sometimes experiences pentimento–where an underlying image in a paint-
ing shows through when overlying layers of paint have become transparent with
age. Also, paint mixtures that include a fugitive pigment may undergo a hue shift,
as the more resilient material’s colorant will dominate as the mixture ages.