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and to always keep it moist; it then becomes softer and
easier to work.
The enamel requires a still more exact preparation, for with-
out it the teeth will appear rough on their exterior surface.
If, on the contrary, the preparation has been perfect, the
enamel will be of a very homogeneous finish, without which
it does not imitate nature.
Neither must this enamel be too vitreous so as to make a
bad contrast with the natural teeth ; it is prevented from be-
coming too opaque, by the addition of a proper quantity of
kaolin.
Incorruptible teeth cannot be baked but imperfectly in
the furnaces which we use ; to obtain its vitrification it re-
quires a considerable degree of heat ; and we are obliged to
have it baked in the furnaces used for the baking of porce-
lain.
It is put in crucibles,* very carefully stopped, and it should
always be recommended to the potter to take them in charge,f
because if the teeth are brought too near the fire, the colour-
ing principles become sensibly weaker, and even sometimes,
(if the heat be too great,) it destroys them altogether.
It is from this cause that the variations are to be attributed,
which are seen in the results. It must here be said, that the
same formulas rarely give twice in succession the same tints.

* The crucibles in which incorruptible teeth are baked, are made with
very argillaceous common earth ; they are of all sizes at the manufactories
of porcelain, and will answer for containing the largest, as well as the most
delicale objects which are submitted to the baking process.
T It is understood by placing to the charge, in putting the caskets in pla-
crs that are farthest off from the fire, so that eventually the teeth receive
bnl a moderate degree of heat, experience having proved, that it was most
advantageous to the developement and preservation of the colouring prin-
ciple of oxides.