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

historically one of the best grades of limonite, contains about 20% iron oxide and
is high in silica. Ochres are among the most permanent hues on the palette and
absorb a medium amount of binder.
Hematite. The native mineral hematite (also hæmatite) is essentially ferric
oxide, occurring almost chemically pure (approximately 95%) without the presence
of water. It has been a source of supply of for natural red pigments since the
earliest classical and ancient times–many other pigments are basically hematite
with varying degrees of mineral impurities such as clay, chalk and silica. Natural
red iron oxides are mostly of dark hue and equally as permanent and dependable
as those synthetically prepared. The high purity leads to high tinting strength
and opacity. The red iron oxides are among the basic, original pigments usually
considered indispensable–one seldom sees a palette that does not contain at least
one of them.
Cold hematite. Familiarly known as Caput mortem, this pigment includes small
amounts of iron sulfate and other impurities usually associated with hematite,
giving the pigment a deep violet hue. It maintains the same qualities as hematite,
as the concentration of ferric oxide is comparable.
Lampblack. This pigment is a black of commercially pure carbon. The finer
varieties are obtained from wick lamps in which fluid fatty oils rich in carbon are
burnt with insufficient air for complete combustion. The soot is collected from
plates held in the flame. Lampblack is a very strong color, whose origin dates back
to antiquity. It has considerable opacity, and is very stable and permanent. It is
very fluffy, of a low specific gravity and absorbs a large portion of binder.
Titanium dioxide. This pigment is a development of the 20th century. It has
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eclipsed other traditional white pigments due to its high opacity, nontoxic nature