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

provide the underlying color to a paint, the binder determines the primary optical
and textural characteristics, as well as the working properties of the paint.
In addition, other substances may be added to further manipulate paint at-
tributes. An artist may add a vehicle to dilute the pigment-binder mixture, allow-
ing the paint to be spread more easily. This substance has no adhesive properties
and evaporates after brush marks have been made. For instance, in oil paint, nat-
ural gum turpentine is often used as a vehicle. Other materials may be added to
enhance the optical or textural characteristics of the paint surface. For years the
strong, and bright colors in Venetian Renaissance paintings mystified art historians.
It turns out that artists were experimental chemists that would mix unconventional
ingredients. Ground particles of glass were added to the palette to enhance the
reflective properties of the paint, which would make objects and figures in their
paintings appear to glow [Goh05]. An artist can also alter the working properties
of the paint, such as viscosity and handling. Many materials (wax, for example)
are added to permit the sculpting of the topology of the surface. Further, one can
even accelerate or deter drying or make the paint more or less fluid, if desired.
Our perception of color in a painting depends on the interactions between light
and the layers of paint. In order to understand how the same pigment looks
different when suspended in different media, we must first analyze the optics of
paint films. When a ray of light hits a surface it is either reflected off the surface,
transmitted through the material, or absorbed into the material.
The way light reacts to a surface is known as the Bidirectional Reflectance
Distribution Function (BRDF) of the surface. This reflection can be as simple as
being uniform in all directions, commonly called diffuse. Diffuse reflections are
typically the result of rough surfaces, and are characterized as matte or dull in
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