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The next series of experiments were made to (leterniiue the relative
porcsit}' of iinderfused and overfused porcelain. In studying the sur-
faces of the cubes of both high and low fusing porcelains under the
microscope, it was found that the surfaces of overfused porcelain were
covered witli little blisters. Underfused porcelain appeared granular
and less dense, while properly fused porcelain presented a denser sur-
face, free from blisters.
The next experiments were to determine the effect of repeated con-
tact of porcelain with the maximum heat required to fuse it. .V cube of
porcelain was fused at a definite degree of heat. A second cube was
then placed beside the first and both heated to the same degree of heat.
Then a third cube was placed beside the two and the three heated to the
heat required to fuse them. This process was continued until the fifth
cube had been fused. The first, second and third cubes were slightlv
overfused and lighter in color, while the fourth was onlv slightly lighter
in color.
The next experiment was to test the effect of repeated heating of
porcelain to the point of biscuiting. This showed that anv of the porce-
lains would finally become fused and maintain their characteristic color.
It is a significant fact that underfused porcelain has a much duller
color and is more opaque, while overfused porcelain becomes lighter
and tends to become more transparent. If porcelain remains in contact
with the maximum heat long enough, it fuses into a glass-like mass.
All the shades of a color from a normal to a light may be obtained by
increasing the heat above the maximum fusing point of the porcelain,
but this is done at a sacrifice of its strength.
It is also a fact that porcelain can be fused, then ground and re-
fused at a lower temperature than the first fusing. And if this process
of re-fusing and regrinding be repeated a number of times, a high fusing
porcelain becomes low fusing. It was also found that the re-fusing and
grinding of the porcelain changed its properties.
The following deductions are made from these
experiments:
Deductions
from experiments. i- Porcelain has no definite fusing point.
2. Bv prolonging the time of exposure to heat,
a thoroughly fused porcelain may be obtained at a comparatively low
temperature.
3. Porcelains fused at a lower temperature for a long time will
maintain their characteristic color, and will be more homogeneous in
texture.
4. Low fusing porcelains can be made of high fusing porcelains
by repeated fusing and grinding.

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