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198 CLASSIFICATION OF DECAYED CAVITIES.

all around next the walls than at the center, for the
reason that a more complete adaptation of the gold
can thus be made, than by any other plan. Some,
however, advocate the opposite practice ; that is, of

keeping the rilling higher in the center than at the
walls, and thus forming an angular space into which
to crowd the gold ; because the gold is thus kept in
more thorough contact with the walls of the cavity;
and it is objected that, to add and consolidate the
gold to the center, while the edges are left higher,
tends to draw them from the walls. This objection,

however, has no force, if the gold is thoroughly con-
solidated as it is introduced.
The cavity is thus filled up, consolidated, and fin-
ished in the usual manner. In adding the last por-
tions of gold, great care should be taken to make a
perfect border to the filling. Crystal gold may be
very advantageously used as a foundation for adhe-
sive foil fillings, as it will retain its position perfectly
in a cavity, where foil would not.
Crystal Gold.—The method of filling this class of
cavities with crystal gold is very simple. The mate-
rial should be annealed just before its use, and then
cut or broken into blocks corresponding with the size
of the cavity to be filled : they may be used as large

as will freely enter the cavity; many small pieces
will be required to fill up interstices or angles. The