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the primaries or secondaries. Orange and violet produce a reddish
brown. Green and orange combine to form a yellowish brown. Green
and violet produce a bluish gray.
Colors have three principal qualities known as
Qualities of Colors. hue, purity and luminosity. These are generally
spoken of as constants. The excessive predominance
of one color over another gives the hue to that color and the greater
this predominance the stronger will be the hue, e. g., when blue and
yellow are mixed green is produced. If yellow predominates, the green
will have a yellowish blue.
The purity of a color is its lack of mixture of white or black, or any
of the colors. These not only weaken the color but change its char-
acter. This can be shown by adding white porcelain to yellow. The
yellow is not only diluted but tends to take a different hue.
The luminosity of a color is measured by the amount of light re-
flected to the eye, and is, therefore, independent of hue or purity. The
most luminous color is yellow, while the least luminous is violet ; be-
tween these extremes are all the intermediate degress of brightness. In
those teeth where light yellow and blue predominate they appear more
translucent, because they reflect and transmit the rays ; while in those
teeth where gray and brown predominate they have a somewhat dull ap-
pearance, because their power of reflection and transmission of light is
not so great, as more of the rays are absorbed on the surface.
Gradations of tint, shade and hue are numerous, according to the
power of perceiving them, and this power greatly varies with different
individuals. Much of the success in coloring depends on the keen and
delicate perception of gradations. One totally unfamiliar with the prin-
ciples of color formation and whose eye is not trained to detect the
delicate hues, rarely sees all of the gradations of color in a tooth, wh'le
one with a trained eye will distinguish hues of colors that are wholly
imperceptible to another.
The pigments most commonly used in the maii-
ufacture of dental porcelain are precipitated gold.
Pigmcnts Used in
Porcelain. platinum, purple of Cassius, the oxids of gold, ti-
tanium, manganese, cobalt, iron, uranium and silver.
The colors produced by the use of these pigments in varying proportions
are red, yellow, blue, green, brown and gray. In referring to red, yellow
and blue, used by the porcelain worker, it must be borne in mind that
only the hues of these colors are used. But for convenience we shall
refer to their hues as the colors.
Red is used extensively by inlay workers. Still all gum enamel frits
are tints of red. It may be added to brown to increase its luminosity. Its

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