Page 163 - My FlipBook

SILICATE IN THE MAKING OP A FILLING 159
to an evaporation in a dry atmosphere or the addition of water
in taking up the condensation from the cold slab at low barometer.
Making- the Mix, Begin with sufficient liquid on the slab and do
not add any more at that stage. Mix by drawing into the liquid
about one-half of the total amount of powder required to make the
completed filling. Begin the mix by spatulating with a light rotat-
ing movement; hold the spatula fiat on the slab, describing the
arc of a small circle with a diameter of say one-fourth of an inch.
As soon as the powder has been all incorporated and the mass ren-
dered uniform, scrape all of the mass off the slab with about three
strokes. Take one-third of the mix each time. This assists in se-
curing uniformity of the mass. Then put it back on the slab this

Fig. 98.—The last stroke of scraping the material from the slab.

time getting all off the spatula. Do not scrape the spatula on the
edge, of the slab, but place it flat on the slab, holding it firmly
and giving it a turn in the hand, which will practically clean it.
Here more powder is added, a small portion at a time, and incor-
porated in the mass already mixed, by the method of crowding,
which is done by rolling the spatula first against one side of the
mass on the slab and then against the other. The addition of the
powder by this crowding process is continued until the mass be-
comes of a consistency of putty, losing practically all of its adhe-
sion and giving only slight evidence of a tendency to follow the
spatula from the slab.
The Proper Consistency is reached when the mass has been mixed