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Enamel Body. A basal body with enough flux added to give it
greater fusibihty than tliat of the foundation body.
Foundation. That portion of an artificial tooth, crown, or inlay,
which takes the place of lost dentin.
Enamel. That portion of an artificial tooth, crown, or inlay, which
takes the place of the lost enamel.
Glaze. .\ highly translucent, colorless, vitrifiable substance which,
when applied to the surface of porcelain fuses at a lower temperature than
the enamel, produces a highly glazed surface.
Plannous Gold. An alloy of gold and platinum containing less than
50 per cent, of platinum.

General Considerations of Porcelain.

In order to understand better the properties of porcelain, it is nec-
essary to consider the ingredients of which it is composed. Such a
consideration shows porcelain to be made up of three classes of sub-
stances. First, the basal ingredients, which are very refractory ; silex
and kaolin, which when heated alone, will undergo intense heat with
practically no change ; and feldspar, a less refractory substance, which
when heated to a high degree undergoes liquifaction. Second, fusible
substances known as fluxes, which fuse at a lower temperature and
increase the fusibility of the more refractory substances; and, third,
metals or their oxids used as pigments.
Silex (Si O2) is the oxid of silicon, and is an
$|lex. infusible substance insoluble in all acids except
hydrofluoric, but slightly soluble in caustic alkalis.
It forms about 13.5 per cent, of the basal mass. It adds strength and
firmness to the porcelain and gives it a more translucent appearance.
Kaolin (2AU O3 Si 0„ 3H, O) is the silicate
Kadin. of aluminum and is composed of aluminum oxid.
silicon oxid and water. It is commonly spoken of
as disintegrated feldspar. Through the natural process of decomposi-
tion feldspar loses its potassium oxid (K„ O) by the action of water
and other agents. Kaolin forms about 4.3 per cent, of porcelain. It is
a very refractory clay when heated alone, but readily unites with feld-
spar when mixed with it. When added to porcelain it gives stability of
form, which property permits unfused porcelain to be molded and
carved.

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