In order to secure the finest optical effect certain proportions have been found necessary. The depth of the crown must be one-half that of the base, and therefore one-third the total depth of the stone, and the width of the table must be slightly less than half that of the stone. The culet should be quite small, not more in width than one-sixth of the table; it is, in fact, not required at all except to avoid the danger of the point splintering. The girdle should be as thin as is compatible with strength sufficient to prevent chipping in the process of mounting the stone; if it were left thick, the rough edge would be visible by reflection at the lower facets, and would, especially if at all dirty, seriously affect the quality of the stone. The shape of the stone is largely determined by the sizes of the templets in the crown and the pavilions in the base as compared with that of the table, or, what comes to the same thing, by the inclinations at which they are cut to that facet. If the table had actually half the width of the stone, the angle[5] between it and a templet would be exactly half a right angle or 45°; it is, however, made somewhat smaller, namely, about 40°. A pavilion, being parallel to a templet, makes a similar angle with the culet. The cross facets are more steeply inclined, and make an angle of about 45° with the table or the culet, as the case may be. The star facets, on the other hand, slant perceptibly less, and make an angle of only about 26° with the table. A latitude of some 4° or 5° is possible without seriously affecting the ‘fire’ of the stone.