, will be destroyed during
the polishing.

The softer materials, such as opal, require treatment more like that
accorded cut glass, and soft abrasive powders, such as pumice, suffice
to polish them. Probably hardly two lapidaries would work exactly alike
in their treatment of precious stones, and each guards his secrets, yet
all use approximately similar general methods. Some have devised
mechanical holders which permit the repeated cutting of stones to
exactly the same angles, and that, too, with an accurate knowledge of
the angles used. These angles can be definitely altered for different
materials, according to their refractive indices. Other lapidaries
produce very fine results by purely hand methods.

These details have been gone into to give an idea of the methods of the
lapidary and of the many variations in method. In general, however, the
_slitting_ or _cleaving_, the _rubbing down_ to shape, the _smoothing
out_ of all scratches and the _facetting_ and _polishing_ are done
somewhat similarly by all lapidaries.

Having now had a glimpse of the methods of the lapidaries, let us
briefly consider what constitutes good "make" in stones other than
diamond.

GOOD "MAKE" IN COLORED STONES. Brilliants, cut from materials having
smaller refractive indices than diamond, (and this group includes nearly
all stones other than diamonds) should have steeper back angles and
higher tops than the best diamond brilliants have. A 35-degree top angle
(the angle between the slope of the top and the plane of the girdle is
called the top angle) and a 41-degree back angle being about ideal for
diamond, other gem materials should have more nearly a 39-degree top
angle and a 44-degree back angle to give the greatest possible
brilliancy. However, in the case of colored gems such as ruby, sapphire,
etc., where the value depends even more largely upon the color than upon
the brilliancy, it is frequently necessary to cut the brilliant thicker
or thinner than these proportions in order to deepen or to thin the
color.

In general, the thicker a stone of a given spread the deeper the color
will be. The color may also be deepened by giving to the stone a rounded
contour, both above and below the girdle, and facetting it in steps
instead of in the brilliant form. Increasing the number of steps also
serves to slightly deepen the color, as a larger number of reflections
is thus obtained within the material, the light thus has to travel a
grea