Brilliant DIAMOND

Brilliant DIAMOND, is that cut in faces both at top and bottom; and whose table, or principal face at top, is flat. To make a complete square brilliant, if the rough diamond be not found of a square figure, it must be made so; and if the work is perfectly executed, the length of the axis will be equal to the side of the square base of the pyramid.—Jewellers then form the table and collet by dividing the block, or length of the axis, into 18 parts. They take $\backslash frac\{1\}\{18\}$ from the upper part, and $\backslash frac\{1\}\{18\}$ from the lower. This gives a plane at $\backslash frac\{1\}\{18\}$ distance from the girdle for the table; and a smaller plane at $\backslash frac\{1\}\{18\}$ distance for the collet; the breadth of which will be $\backslash frac\{1\}\{2\}$ of the breadth of the table. In this state the stone is said to be a complete square table diamond.—The brilliant is an improvement on the table-diamond, and was introduced within the last century, according to Mr Jefferies.—To render a brilliant perfect, each corner of the above described table-diamond must be shortened by $\backslash frac\{1\}\{18\}$ of its original. The corner ribs of the upper sides must be flattened, or run towards the centre of the table $\backslash frac\{1\}\{2\}$ less than the sides; the lower part, which terminates in the girdle, must be $\backslash frac\{1\}\{2\}$ of one side of the girdle; and each corner rib of the under sides must be flattened at the top, to answer the above flattening at the girdle, and at bottom must be $\backslash frac\{1\}\{2\}$ of each side of the collet.

The parts of the small work which completes the brilliant, or the star and skill facets, are of a triangular figure. Both of these partake equally of the depth of the upper sides from the table to the girdle; and meet in the middle of each side of the table and girdle, as also at the corners. Thus they produce regular lozenges on the four upper sides and corners of the stone. The triangular facets, on the under sides, joining to the girdle, must be half as deep again as the above facets, to answer to the collet part.—The stone here described is said to be a full-substanced brilliant.—If the stone is thicker than in the proportion here mentioned, it is said to be an over-weighted brilliant.—If the thickness is less than in this proportion, it is called a spread-brilliant.—The beauty of brilliants is diminished from their being either over-weighted or spread. The true proportion of the axis, or depth of the stone to its side, is as 2 to 3.—Brilliants are distinguished into square, round, oval, and drops, from the figure of their respective girdles.