IMPROVING THE BOWTIE EFFECT
By Joe C. C. Yuan-- G.G., D.G.A.
Anyone who has worked on marquise-, pear- or oval-shaped diamonds knows the fancy cuts of these relatively longer shapes. In the middle of the diamond, there is a bowtie or a dark shadow in the shape of a bowtie (Fig. 7-1) -- some of them are larger in size while others are fairly slight. Almost every diamond has this bowtie which is due to incorrect facets arrangements. This has made potential customers of fancy diamonds change their minds at the last moment. Store owners' common explanation is that the bowtie-shaped shadow is unavoidable.
Marquise-, pear- or oval-shaped diamonds are appealing to buyers primarily because they are different in shape from the brilliant round ones. Secondly, at the two ends of these diamonds, there are gleams of scintillation which move along with the diamonds' movement. It is like the galaxy of a summer night: when we narrow our eyes and move our heads from side to side, the stars before our eyes seem to move with us.
The girdle of the fancy-cut diamond must be polished into transparent facets because the angles at the two ends of the bottom of the diamond are flat. If the girdle is brutted, the scintillation of the two ends will appear clouded over with a whitish color as shown in Fig.7-3. This will affect the brilliancy of the diamond and cause a milky feel. If the girdle is polished into transparent facets, the milky feel will disappear and the brilliancy will improve as shown in Fig. 7-4. This is true for diamonds of different sizes. From time to time there are small marquise diamonds on the market. When we look at them from the top, they are noticeably lacking in brilliancy as their girdles are brutted. The girdle must be faceted to increase the brilliancy of the diamond.
The bowtie effect of fancy-cut diamonds has varying degrees of dark shadow owing to different ways of cutting and proportion.
Fig. 7-5 shows the worst case of bowtie which is a large, rigid and dark shadow. If the diamond is held with a pair of tweezers at the two ends, when it is moved back and forth, the bowtie-shaped shadow seems to be broader and doesn't move accordingly. If the main pavilion facets at the belly bottom are steep, like the way of cutting and facets arrangement shown in Fig. 7-5. Fig. 7-6. The bowtie is slightly less broad and the dark shadow moves when the diamond is moved back and forth. In Fig. 7-7 show the cutting and facets arrangement to be narrower and has a dark strip of shadow which visible as it moves swiftly when the diamond is moved. The contrast of brightness also changes at the same time. Fig. 7-8 shows the culet of the opposite main facets are at the middle of the belly and it comes to the center of a point or near a point. The horizontal position between the main belly facets and their lower girdle facets at both sides are different. The width of these four lower girdle faces are narrower. When the height of lower girdle facets are about 85-90% from girdle to the culet (as is shown in Fig. 7-9), then only a line of dark shadow will be seen. The line of the shadow moves extremely swiftly with the movement of the diamond and a sharp contrast of brightness appears. In Fig. 7-10, the bowtie effect will entirely vanish if the method of cutting and facets arrangement is followed. This method, however, is only used in South Africa by a very small group of diamond cutters.
The majority of the diamonds available on the market are cut with the methods as are shown in Fig. 7-5 to 7-8. The cutting method illustrated by Fig. 7-11 is rarely seen on the market. Two pavilion main facets are cut from the culet to the two ends. However the angle is so shallow that one can see through the diamond. The drawback of this cutting method is that the diamond has very poor refraction and there will definitely be a black bowtie. Fig. 7-11 only applies to marquise- and pear-shaped points. Fig. 7-12 is only for small- and medium-sized, marquise- and -pear-shaped pointed ends. There are four pavilion main facts at the bottom, but there are still sixteen lower girdle facets. The height of these lower girdle facets should be 85-90% from girdle to culet. The effect will be impressive for small-sized, marquise-shaped diamonds, since it reduces the range of the bowtie. However, larger diamonds appear to be too monotonous because there are only four pavilion main facets. This cutting is used in Israel.
The Arc of the Girdle is Best When It Has a Flat Plane
Take marquise for instance, as shown in Fig. 7-13, which is a side view from the bottom up. The girdle is quite low at the middle while the two pointed ends are high. As a result, there is a rather obvious bowtie effect and the refraction and the scintillation of the diamond are far from being ideal. If recut to achieve better effect, quite some weight will be lost in the process. The best girdle is illustrated in Fig. 7-9 when the entire girdle is approximately on the same plane. Of the two opposite pavilion main facets at the middle of the girdle should be slightly higher. Although this will also create a rather broad bowtie, less weight will be lost in the recutting process than is the case shown in Fig. 7-13.
Polishing of the Crown
Take the marquise for instance. There are two ways of cutting the crown, as are illustrated by Fig. 7-15 and 7-16. Most of the diamonds seen on the market are cut with the way of Fig. 7-15, i.e., a kite facet is added at each of the two pointed ends. In so doing, a better effect of refraction will be achieved. There are only six kite facets in Fig. 7-16, which is better suited for small marquise.
Improving the Bowtie Effect
For the visible bowtie in fig. 7-7 and the flat girdle in Fig. 7-9, a good effect can be achieved if the are diamonds recut to the way of Fig. 7-8, about 2-5% of weight will be lost in the process. If the girdle is like Fig. 7-13, about 5-8% of weight will be lost to achieve the effect of Fig. 7-8.
In order to achieve the effect of Fig. 7-8 on the basis of the bottom in Fig. 7-6 and the girdle of Fig. 7-9, about 5-10% of weight will be lost. About 10-15% of weight will be lost if the girdle in Fig. 7-13 is to be improved to the effect of Fig. 7-8.
In order to achieve the effect of Fig. 7-8 on the basis of the bottom in Fig. 7-5 and the girdle of Fig. 7-9, about 10-15% of weight will be lost. If the girdle in Fig. 7-13 is to be improved to the effect of Fig. 7-8, about 15-20% of weight will be lost.
So as to achieve the effect of Fig. 7-8 on the basis of the bottom in Fig. 7-11 and the girdle of Fig. 7-9, about 5-15% of weight will be lost, depending on the width of the bottom, belly and pavilion main facet. If the girdle in Fig. 7-13 is to be improved to the effect of Fig. 7-8, about 10-20% of weight will be lost.
For a larger marquise diamond to be improved from a four main-facets cut bottom like Fig. 7-12 and a girdle like Fig. 7-9 to the effect of Fig. 7-8 or 7-10, a 2-5% weight loss will occur. An improvement from the girdle in Fig. 7-13 to the effect of Fig. 7-8 will cause 5-8% loss of weight. And an improvement from the bottom in Fig. 7-8 and the girdle in Fig. 7-13 to the girdle in Fig. 7-9 will result in about 4-6% of loss of weight.
The round end of oval and pear-shaped diamonds are, as shown in Fig. 7-17, cut mostly in the same way as round brilliant cut. This way of cutting is preferable for diamonds that are short and thick. As for the small portion of oval and pear diamonds that are thin and long shapes are cut to Fig. 7-18.
The bowtie shadow in marquise-, pear- and oval-shaped diamonds very often becomes the negative factor in the sale of fancy-cut diamonds. The situation, however, can be improved upon if better methods of cutting and facets arrangements are adopted. Even in those cases where the limit of weight is an obstacle and only partial changes can be done, the size of the bowtie effect can be considerably reduced or the bowtie's movement can be improved. Thus a better overall effect is achieved.