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Chapter U.
Some Phenomena of Color in Porcelain Inlay Ulork.

The phenomena of color should be studied in a theoretic and prac-
tical manner, and the sources of light should be considered. Light has
been defined as that form of radiant energy that acts on the retina of
the eye and renders visible the objects from which it comes. An object
is visible, either because it gives out light of itself (self-luminous), or
because it reflects light from its surface (illuminated). The light of the
sun or the flame of a lamp are examples of self-luminous bodies, which
emit luminous rays in all directions. Light emitted from the sun is
said to be white light, while that from artificial sources is said to be
colored light. Sunlight is represented by white, while darkness is repre-
sented by black.
Color is a sensation produced in a variety of
Color Defined. ways, but pre-eminently by the action of light on
the retina. The specific efifect produced depends
upon the character and combination of rays that reach the retina. The
source of color is light, and it is lost or destroyed bv darkness. Colors
are divided into inherent and transient. Inherent colors are material
or colored substances such as the pigments used by the dyer, painter,
etc. Transient colors are those formed by the decomposition of light,
such as those of the rainbow or the prism.
Some of the phenomena of light which assist in producing colors
from pigments are absorption, transmission, reflection, and refraction.
If a pigmented transparent body absorbs certain colored rays and trans-
mits others, it will appear to be colored from the combination of the
transmitted rays. A translucent body transmits, reflects, and absorbs
rays and its color is determined by the quality of light reflected or trans-
mitted. If light penetrates a short distance into a body, and is then re-
flected, its surface generally appears to have the colors of the reflected
rays. Light is not transmitted by opaque substances, but the rays are
either reflected or absorbed. When, therefore, light is incident upon an
opaque body, it is wholly excluded from the opposite side. A light beam
passing from one medium into another of different density is bent or
refracted at the boundary plane between the two media. This deviation

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