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14- Underfused porcelain has a much duller liue and is more opaque,
while overfused porcelain becomes lighter and tends to become more
transparent. All the shades of a color from dark to a light may be
obtained by increasing the heat above the maximum fusing point of the
porcelain, but this is done at the sacrifice of its strength.
15. The tendency of both high and low fusing porcelains is to as-
sume spheroidal form when overfused. and if considerably overfused
they tend to form an amorphous mass of -glass.

Fig. 3.

Figure 2 shows four cubes of low fusing and four cubes of high
fusing porcelain each heated separately to the state of hard biscuit.
Figure 3 shows the effect on the form of the mass by overfusing porce-
lain. All of these cubes w-ere fused at the same time and heated to a
degree of heat sufficient to overfuse the foundation bodies.
The first three cubes ran together into an amorphous glass-like
mass, while the fourth cube formed an amorphous mass to itself. The
fifth cube, which was an enamel body, changed to an irregular spher-
oidal form and the last tliree cubes became rounded at the edges.
The process of fusing porcelain is largely a chemical reaction,
brought about by the various ingredients combining to form multiple
silicates of aluminum, potassium or sodium with the liberation of gases.
The method of fusing porcelain at its maximum temperature for a
short time is to be condemned. It makes the porcelain more brittle and
causes the formation of minute bubbles throughout the entire mass, for

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