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476
portions, it makes the greatest varieties of yellow ; and
mixed with other oxides, it contributes to give the teeth the
most natural tints.
§ v. Of the Oxide of Zinc.
The oxide of Zinc is very fusible in the fire, and becomes
yellow : it gives this colour to enamel ; but if submitted too
long to a high degree of heat, the yellow colour becomes
light, and sometimes altogether disappears. Nevertheless, it
is useful to use it alone or mixed with with other oxides ; for
my part, I only employ it in uniting it to the oxides of gold
and titanium.
§ vi. Of the Oxide of Uranium.
The oxide of uranium is like cobalt, it makes a «blue col-
our ; it differs merely from the latter in the blue colour that
it gives bordering a little on the green : it was for this reason
I preferred it to cobalt, because I remarked that this shade
united better with those of the other oxides. Combined
with the oxides of gold and titanium, it gives an agreeable
colour.
It is with the enamels with which they combine it, that
they obtain teeth of a bluish tint, which are often obliged
to be replaced. In this manner uranium is very useful ; but
it is wrong to suppose we may obtain yellow tints with this
oxide ; the experience to which, we have submitted it, autho-
rises us to consider as erroneous the assertions giving it the
properties of making this colour.
Its colouring principle is very strong ; so much so, that it
cannot be used but in very small proportions.
476
portions, it makes the greatest varieties of yellow ; and
mixed with other oxides, it contributes to give the teeth the
most natural tints.
§ v. Of the Oxide of Zinc.
The oxide of Zinc is very fusible in the fire, and becomes
yellow : it gives this colour to enamel ; but if submitted too
long to a high degree of heat, the yellow colour becomes
light, and sometimes altogether disappears. Nevertheless, it
is useful to use it alone or mixed with with other oxides ; for
my part, I only employ it in uniting it to the oxides of gold
and titanium.
§ vi. Of the Oxide of Uranium.
The oxide of uranium is like cobalt, it makes a «blue col-
our ; it differs merely from the latter in the blue colour that
it gives bordering a little on the green : it was for this reason
I preferred it to cobalt, because I remarked that this shade
united better with those of the other oxides. Combined
with the oxides of gold and titanium, it gives an agreeable
colour.
It is with the enamels with which they combine it, that
they obtain teeth of a bluish tint, which are often obliged
to be replaced. In this manner uranium is very useful ; but
it is wrong to suppose we may obtain yellow tints with this
oxide ; the experience to which, we have submitted it, autho-
rises us to consider as erroneous the assertions giving it the
properties of making this colour.
Its colouring principle is very strong ; so much so, that it
cannot be used but in very small proportions.
