Page 73 - My FlipBook

and swaging with tape. Care should be exercised to exert uniform
pressure on the margins of the matrix during the process of swaging
(F'g- 79)-
It is probable that the seat of the matrix will be torn during the
process of burnishing (Fig. 80 A), but such tears in the seat of a matrix
do not affect its efficiency. Sometimes, moreover, the matrix may tear

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Fig. 79.

at some point along the labial or lingual margins (Fig. 80 B). If this
tear is small, it need be considered of no consequence. Large perfora-
tions in the region of the seat and small ones along the margins of the
matrices for high fusing porcelain may be bridged before applying the
porcelain by painting the cavity side of the matrix with a thick solution
of shellac (Fig. 81 A), which prevents porcelain from flowmg through
the perforations, and burns from the matrix without leaving a residue.
It is advisable to coat a perforation at the margin before each applica-
tion of the porcelain in order to insure a smooth margin of porcelain after
the matrix has been removed.

69