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CHAPTER XLIV.

THE CONSTRUCTION AND PLACING OF A PORCELAIN
INLAY

Following the completion of cavity preparation the next step in
porcelain inlay filling is the formation of a matrix.
A Matrix is a thin piece of metal shaped to the cavity form in
which the porcelain is fused.
Matrix Material. The matrix materials in common use are pure
gold, pure platinum and platinized gold. Pure gold and platinized
gold can be used only with what is termed low fusing bodies,
while pure platinum can be used Avith either high or low fusing
bodies. Gold is more easily shaped to cavity form, but tears more
easily and does not hold its shape as well after burnishing.
Thickness of Foil. The most popular thickness of platinum foil
to be used in the construction of a matrix is 1-1,000 of an inch.
Thicker than this is difficult to manipulate, while the thinner foils
tear too easily, and are more liable to distortion during the
processes of building and fusing.
Annealing of Matrix Material. This is best accomplished by
placing the entire sheet of material as it comes from the supply
house in the electric oven and bringing it to the desired tempera-
ture before cutting off the piece desired for the case in hand. Pure
gold and platinized gold should be brought to the full red heat or
about 1,200° or 1,300° F. Platinum should be carried up as high as
it is expected to carry the temperature during the process of fusing
and held there for two or three minutes. It is not necessary to an-
neal several times during the process of shaping the matrix.
Methods of Forming the Matrix. There are three general
methods in use for the construction of a matrix. First, burnishing
directly into the cavity. Second, swaging over an impression of
the cavity. Third, swaging into a model of the cavity.
Each has its advantage in different cases and are recommended
by all porcelain workers. However, the combination of the first
and second methods will bring good results and is the method re-
quiring the least time.
Technic of the Combination Method. First take an impression
of the cavity. If the cavity is large it is best to use modeling com-
pound, trimming off that part which flares out over the external
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