The standards applied in grading fancy cuts are not as strict as those for judging brilliant cuts. This is because of the very great variety of shapes which are possible in fancy cuts. On the one hand the shape of the stone is determined by the natural shape of the rough diamond. In order to save on weight the cutter will therefore seek to suit the shape as far as possible to the rough stone.
On the other hand, evaluation of proportions partly depends of the subjective feelings of individual persons. One person will prefer slender, elongated navettes, while another person will attach greater value to a broad shape.
In any event the shape must be properly proportioned. For example, excessively large curvatures or indentations in a pear, oval or heart shape are very unsightly and unattractive, and as a result the stone undergoes a (subjective) devaluation during the evaluation of the cut (Fig 350).
|Fig 350 Badly proportioned shapes||Unsymmetrical shapes|
In the emerald cut the edge lengths of the corners ensure a balanced harmony in the shape of the cut. There is no ideal yardstick, and in the final analysis judgment has to be left to the visual experience of the grader.
Whether brilliant, marquise, pear, emerald or heart shape, they are all subject to the laws of optics and have to be cut within certain tolerances according to certain mathematical guidelines if their optimum brilliance is to be brought out. The influence of fashion will occasionally give preference to certain styles of cut.
The "relative" beauty of the stone forms the basis of stone grading, while the demand for maximum brilliance and dispersion takes precedence. At the same time, however, the form of cut and the ratio of length to width also have to be considered. Thus:
|Pear||1.50: 1 to 1.75 :1
greater than 1.75 : 1 to 2.00 : 1
less than 1.50 : 1 to 1.25 : 1
greater than 2.00 : 1
less than 1.25 : 1
|Navette||1.75 : 1 to 2.25 :1
greater than 2.25 : 1 to 2.50 : 1
less than 1.75: 1 to 1.50: 1
greater than 2.50 : 1
less than 1.50 : 1
In the measurement of proportions in millimeters, length, width and height are recorded and at the same time serve to assure identity.
In all fancy cuts the maximum extent of the width is always formed by the girdle diameter which is used 100% as the basis for all further measurements of proportions.
|Fig 351 In fancy cuts the width amounts to 100% of the girdle diameter|
In measurements made in the PROPORTIONSCOPE the stone is adjusted 100% in this direction and a reading is taken from the screen for all further proportions, exactly as in the case of brilliants.
With measurements of this kind care must be taken that the culets and the tips of the stones are introduced accurately Into the perforated sleeve of the PROPORTIONSCOPE and that the upper pin is perpendicular to the table. This guarantees that the stone is not lying at an angle in the stone holder. The greatest care is especially called for in the case of emerald cuts with very thin. edge-type culets.
As with a brilliant cut stone, the size of the table is measured from corner to corner. Without exception in all fancy cuts this applies to the width.
|Fig 3.52 Measuring the size of the table|
It is surprising to observe occasionally extreme measurements (for inst. 70%) which, when judged visually, "fit" a stone and can be graded as "very good".
The girdles of modified brilliant cuts and other types of cut are nearly always facetted or polished, generally a little more so than in the case of a brilliant, and especially so at the points of navettes, drops and at the indents of a heart-shape, because these spots are especially endangered through accidental damage and while being set. Therefore this should not be taken into account when grading the width of the girdle. The step-cuts-emerald and square often have knife-edge girdles.
Although in principle the proportion of crown to pavilion should have the same tolerances in a fancy cut as in a brilliant, one occasionally can be surprised by the measurements read off the PROPORTIONSCOPE. For instance, an emerald cut which appeared to have a very good brilliance, is seen to have a height of pavilion of 50%. Objective measurements and subjective, visual observation have to be taken into consideration. When judging the cut of fancies, the latter should be acknowledged as the cutter of the fancies can often make good poor proportioning by various other means, such as additional facets or the positioning of the culet.
A result of a high pavilion in fancy cuts as well as in brilliants can be brilliance poor zones in the table. These have mostly the shape of a "bow-tie".
|Fig 353 Brilliance-poor grey zones show up poor proportions|
The higher these pavilions, the darker these zones, so that one can easily recognize them visually. The effects is of course a reduction in brilliance and a lower cut grade.
When measuring the proportions of a step-cut on a PROPORTIONSCOPE, the picture often shows a rounded outline.
Ideally, the pavilion should be as near to that of a brilliant as possible and the three rows of step-like facets only slightly angled to each other. Should these angles be obtuse, the appearance becomes rounded, the brilliance is reduced, but weight is saved. This "overweight" can be as much as 15% and is negatively graded.
|Correct Overweight||5% overweight||10 % overweight||15% overweight|
|Fig 354 "Overweight" of emerald cuts due to a rounded pavilion i.e. cut for weight|
The culet of a fancy cut can be a point or a line. The culet should be in the centre of the stone, i.e. in the middle of the widest part of the shape, except in the case of a drop where it should be in the centre of an imaginary circle (Fig 355 c).
|Fig 355 Position of the culet in fancy cuts|
As in the case of brilliants, the culets should be small and easily discernible with a 10 x loupe.
Due to the position of the culet, the cutter is able, in the case of step cuts, to influence the pavilion angle, as the longer the culet, the wider is the pavilion angle.
With emerald cuts the culet should not be longer than the total width of the stone (Fig 355 e).
Symmetry and external features
Basically the same standards apply as in the case of brilliants and they influence the execution of the cut to the same extent.
|Polishing marks||Further fancy cuts of diamond|