Page 271 - My FlipBook

GOLD. 269

degree of heat, and the ability to render another make of equal purity
cohesive by the application of a similar degree of heat. It has been
claimed by some manufacturers of dental gold foils that they are able
to procure from the same ingot samples of non-cohesive, semi-cohesive,
and extra-cohesive gold, attaining these physical properties of the mate-
rial without alloying with other metals. This has led to the belief
that, since absolutely pure gold possesses inherent cohesive properties,
some metallic salt or other foreign substance has been deposited upon
the surface of the leaf of non-cohesive foil which has the power of pre-
venting the union of the surfaces of the foil when contact is sought.
It has been surmised that a thin film of iron has been deposited upon
the surfaces of the leaf of non-cohesive foil, for the reason that if a
leaf of such foil be melted into a globule, it presents a reddish brown
appearance, Avhich is not true of the leaf of cohesive foil when melted
as above.
Much of the so-called non-cohesive foil offered for sale is not,
strictly speaking, of this variety, as the application of moderate heat
will render it quite cohesive. It possesses the softness peculiar to pure
gold foil, but it should not be classed with the variety which does not
weld with other particles of the same metal except when subjected to
great heat.
It has been claimed by some that non-cohesive foil has no place in
dental practice—that any tooth which can be filled with gold may be
filled with cohesive foil. This statement may be true in the main, but
it is also true that many teeth having strong cavity walls can be just as
well filled where a large portion of the filling is made with non-cohe-
sive foil, and with a great saving of time. Adaptation, not hardness,
constitutes the saving quality in cavity filling.
As most non-cohesive foil is prepared in the form of sheets and
is placed in books containing one-eighth of an ounce, the operator is
compelled to prepare it in some form suitable for introduction to the
cavity. The size and shape of the cavity will be some guide as to the
best method of preparing the gold. The narrow tape, the mat, the
tightly rolled cylinder, and the roll or rope are the forms best adapted
for the use of non-cohesive gold foil.
The tape is best made by taking one-half or one-third of a leaf of
No. 4 or No. 5 foil, laying it upon a table napkin of medium size folded
square as it comes from the laundry ; the napkin is then taken in the
palm of the left hand, and the foil spatula is placed in the middle of
the piece of foil ; the hand is then closed tightly, thus folding the nap-
kin, likewise the foil, upon the sides of the spatula. This process is
repeated until the tape is one-eighth or one-sixteenth inch in width
(Fig. 222).