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

However, while the photographs are not completely physically accurate depictions
of the actual color of the samples, they do give the viewer a reasonable subjective
comparison.
An important observation occurs when viewing the variation in binding media
over the visible spectrum. Typically, the specific pigment determines the general
shape of the spectral curve. That is, the intrinsic chemical properties of the ma-
terial from which the pigment was created determines the central tendency of the
material’s reflectance, as well as the wavelengths that are primarily absorbed. Yet,
the specific binding media determines the exact behavior of how light behaves when
striking the material. Each material has its own characteristics that it imparts and
one recognizes these differences in a work of art. A painting in one media will in-
voke a different sensation than that created in a different media. This relationship
holds for all of the pigments in the study.
This observation is logical; as one of the criteria for a binding material is that
it does not drastically affect the materials that are suspended within it. An artist
expects a pigment to maintain a relatively specific hue, whether it is dispersed
in oil or watercolor or another media. However, as seen with Lapis Lazuli, while
the general color is similar between binding media, there is great variation in the
resulting color between the different materials.
A common way to compare colors is to transform them into a perceptually uni-
form color space and study the results. This allows one to quantify the magnitude
of the difference between colors. In our case, this can be used to evaluate how
much binding materials affect the color of a pigment.
The basic computation is to first convert the spectral data into CIE tristimulus
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values XY Z. This is done using the response matching functions, an illuminant