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178 FILLING MATERIALS

ing at a new point after the first annealing, and repeating the
process to prevent the occurrence of partially annealed spots

in the gold, with the resultant tendency to pitting in the filling.
The use of a gold annealer is the most satisfactory method.
If a mica or soapstone tray is used, the student should be careful
to see that the flame of the lamp is given sufficient heat to properly

anneal the gold, else poor fillings from failure to bring out its full
cohesive property will be the result.
Gold Pluggers.—Gold pluggers are made with numerous
serrations in their face, these serrations being of a wedge or
pyramidal shape. A set of gold pluggers should possess
serrations of the same size in each instrument, in order that
when change of instruments is made during the gold-building

operation, the pyramids may properly interdigitate (see Figs.
87, ^^, and 89). In case instruments with different size ser-
rations are used, when a change to a new instrument is
made, the surface of the gold should be gone over with the

new instrument before adding a fresh piece of gold.
There are three principal methods of plugging cohesive
gold:
1. By means of hand pressure.
2. By the use of the hand mallet.
3 With some form of mechanical mallet.

For starting fillings, hand pressure alone should be used,
while for building the main body of the filling, either the hand
mallet or some form of mechanical mallet is utilized. For
operations in the technic laboratory, the student may confine
himself to hand pressure and the hand mallet, as very excellent

work may be done by this method, although, if desired, the
automatic mallet may be used in addition. The operations
may be performed with cohesive tin instead of gold, and ex-
cellent practice obtained in that manner. The student should
perform, though, at least a few gold-building operations.