blue,
"indigo " sapphires, in contradistinction to which the palest of the
stones are called " water " sapphires. The colouring matter is not
always even, but is often spread over the substance of the stone in
scabs or " splotches," which rather favours imitation, and, where this
unevenness occurs, it may be necessary to cut or divide the stone, or
so to arrange the form of it that the finished stone shall be equally
blue throughout.
In
some cases, however, the sapphire may owe its beauty to the presence of
two, three or more colours in separate strata appearing in one stone :
such as a portion being a green-blue, another a cornflower blue,
another perfectly colourless : another a pale sky blue, another yellow,
each perfectly distinct, the stone being cut so as to show each colour
in its full perfection.
This
stone, the sapphire, is hardness No. 9 (see "Hardness" table), and
therefore ranks next to the diamond, which makes it a matter of great
difficulty to obtain an imitation which is of the same specific gravity
and of the same degree of hardness, though this has been done. Such
stones are purchasable, but though sold as imitations at comparatively
low price, and the buyer may consider them just as good as the real
gem. to the experienced eye they are readily detectable.
By
heating a sapphire its blue colour slowly fades, to complete
transparency in many cases, or at any rate to so pale a tint as to pass
for a transparent stone. Valuable as is the sapphire, the diamond is
more so, and it follows that if one of these clear or " cleared"
sapphires is cut in the " rose " or " brilliant " form— which forms are
reserved almost exclusively for the
