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1/2 MECHANICAL DENTISTRY AND METALLURGY.

expose the sides of the backing and the lower l)order of the
band, as ihiistrated in Fig. 137, but every portion of the
porcelain should be protected.
Soldering and Finishing.—The case should then be at
first gently heated up to drive off the moisture, then trans-
ferred to the soldering block, when, with the blowpipe.
more heat should be applied until the investment and tooth
are thoroughly and evenly heated throughout. Gold solder.
18 k., is then cut in small pieces and placed, with a little
borax, over the aperture betw^een the backing of the tooth
and the cap. The investment being now uniformly heated,
the flame from the blow^pipe should be directed upon the
solder, mostly in the direction indicated in Fig. 137, when,
if the entire case has been previously brought to a red heat,
the solder will readily melt and flow between the tooth and
cap. Additional solder should now be added and melted
until the proper contour of the tooth is insured.
The tooth and investment should then be placed in and
covered with sand, plaster, or some other suitable substance
to keep the heat from radiating too rapidly and thus crack-
ing the tooth. It should be left so covered until it is thor-
oughly cool. We might add here, that it is well to direct
the flame from the blow-pipe into the sand or other material
for a moment before placing the tooth in. After the tooth
is thoroughly cool, the investment may be
^^'_^'^
broken away, and all oxidation and borax re-
moved by placing it for a fcic iiiiuutcs in tJic
acid bath. The crown is then ready to be
finished and polished. The shaping of the
solder can best be done with carborundum
stones, followed with hard-rubber discs, and
then fine sand-paper or cuttlefish discs, while
the final polishing is accomplish.ed with brush
and buff-wdieels, pumice stone, whiting, and rouge. The
completed crown in position is shown in Fig. 138.