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

Cobalt Blue. This chemical reaction produces particles of unusual fineness and
uniformity. On the other hand, the natural pigment Azurite is prepared by crush-
ing samples of the mineral extracted from copper ore deposits. During this process,
aggregates of copper carbonate crystals are shattered into small, irregular shapes
and sizes. Due to difficulties in extraction, the mineral may also contain inclusions,
which are small amounts of other minerals (malachite, in this case). As a result,
while exhibiting a similar hue, Azurite’s reflectance properties will not compare to
the purity of those found in Cobalt Blue.
The driving force of synthetic pigments mainly serves the dye and paint in-
dustries. They are formulated today to maximize their desirability–homogeneous
in shape, size and composition–while at the same time improving color nuances,
brightness and stability. For example, to increase the covering power of a pigment,
particle sizes are reduced to the smallest possible (therefore increasing the possi-
bility of poor lightfastness). Particles that are more consistent in shape and size
also tend not to settle quickly and nor separate from their binder once inside a
paint bottle or tube. While this increases the shelf life and thereby marketability
of paint, commercial additives and processes sometimes reduce the color’s effec-
tiveness for artists’ use.
2.2.2 Binding Media Influence
In the previous section, pigments have been discussed out of context. Pigments
themselves do not have binding strength and therefore are never viewed directly
on a painting. The material that adheres pigment particles to the ground is known
as the binding medium. Many types of binders have been experimented with over
the years, including plant gums, animal glues and drying oils. While pigments
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