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54 PRECIOUS STONES.
diameter
of the collet be taken as unity, the girdle should be nine units in
diameter, and the table five ; also the vertical distance from table to
girdle should be one-half the vertical distance of the collet from the
girdle. These proportions give the outline shown in Fig. 7, and as will
be seen from Fig. 3, the angles thus formed are eminently adapted to
repeatedly reflect the light within the stone. The exact finished form
of the stone is by no means fixed, but is modified by the cutter to
suit the rough gem he is dealing with, so as to sacrifice as little
material as is consistent with giving a good result. In the case of
colourless and transparent stones the proportions given above are
adhered to more or less closely ; but the plan of the stone may be
considerably modified. Thus it may be generally circular, as in Fig. 7,
or square or oblong, as in the Pitt or Regent Diamond (Fig. 8), or
triangular, etc. Again, a coloured stone is usually cut in a rather
more shallow form; the deeper the colour, usually, the thinner the
stone. If the stone were of the proportion of a colourless gem the tint
might be so deep as to lose a great deal of its beauty.
The
presence of a flaw or other imperfection may conÂsiderably modify the
form given to the finished stone ; as a rule the English cutters prefer
to have the gem perfect technically even at the sacrifice of a good
deal of weight, and hence flaws are either removed altogether, or at
least the stone is so cut that the flaw comes in the girdle, where it
is not so conspicuous. The slightest imperfection in the region of the
collet has a very great influence on the appearance of the gem, as it
is reflected again and again, and thus seemÂingly magnified. The
triple-cut brilliant form is only given
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