Importance of Cutting in Gemstones




The average jeweler fails to recognize the great importance of cutting as it affects the beauty and sale ability of gemstones. Too often he purchases stones for stock on the basis of the greatest weight or the greatest "spread " for the money invested. He does not realize that a correctly cut smaller stone at the same price is by far the better investment, because its added beauty appeals to almost every customer. Obviously, a stone with a wider appeal is likely to sell in a shorter period of time.

Practically all colored stones reaching the market today are cut in a manner that fails to show their maximum beauty of color; i.e., with the facets near the center of the base almost parallel to the top facet. Thus the visible color and bright reflections are confined largely to the edges of the stone and the center appears as a nearly colorless "window", through which the ring shank or the finger of the wearer is easily visible. This detracts from the beauty of the stone and often removes the appeal it would otherwise have for a customer.

Many lapidists claim that they cut stones with thin backs because standard mountings have such shallow settings that properly cut stones protrude from the bottom and rest against the finger of the wearer. Others claim that they must be cut in this manner to bring out the color of the stone. The truth is that invariably they want to retain maximum weight from the rough or reduce the cost of cutting by rushing the job so much that it is impossible to maintain proper angles and proportions. Actually, the necessary depth for maximum brilliancy and color in stones of lower R.I. is not an abnormal depth. In fact, many of the stones displaying "windows" have sufficient depth, but the angles of the pavilion facets depart so greatly from the correct angles that it is impossible for the stone to show maximum total reflection and depth of color. Colored gems should be cut so that the pavilion facets on each side correspond to almost straight lines, the angles of which vary slightly for different species. In Figure A the first drawing shows the proper proportions and angles for a gem of a particular species. The additional drawings show typical examples of excess weight retention as a result of improper cutting of stones of the same species. The dark silhouettes indicate how these stones should have been cut.

To fashion colored stones properly requires not only the use of proper angles and an excellent polish, but the proper orientation. Correct orientation assures the most attractive color when the stone is examined through the table; i.e. "face up". It is not the same for all gemstones, but depends on the strength of pleochroism and the attractiveness of the pleochroic colors. When cutting alexandrite, for example, it is necessary that the red trichroic color be seen through the table, so that a maximum color change will be visible under different lighting conditions when the stone is mounted.

Methods and styles of cutting gemstones

With a gem materiel that possesses easy cleavage, it is sometimes necessary to orient it so that a cleavage direction is not parallel to a polishing direction, rather than allowing the most attractive color to be the only controlling factor in determining orientation. In actual cutting, a compromise orientation is often achieved between the best color direction and the easy cleavage direction or directions.

Other factors may also enter into the cutting of a gem. For example, the inclusions that make possible the cat's-eye effect in chrysoberyl must be oriented so that the light reflected from them, will produce a sharp eye. If there are not enough inclusions in the stone to cause a sharp eye with a normal cabochon shape, the cutter often makes the cabochon very high in relation to its width in order to sharpen what chatoyancy is available.

All of these factors are of great importance to the lapidist, since it is his duty and to his advantage, to obtain maximum beauty from a piece of rough. The jeweler does not need to know how to orient gemstones to produce maximum beauty, but the must know whether the potential beauty has been brought out sufficiently to justify the price he is being asked to pay. If in an alexandrite, to continue the earlier example, the color change seen through the table is weak but the stone shows a strong color change through the girdle direction, the jeweler should only consider the color change that will be visible when the stone is mounted and only pay a price that is commensurate with the weak color change. Although the strong color change can be seen when the stone is loose, that has no value to the buyer. When it is mounted only the weak change will be apparent. In the same manner, a jeweler should refuse to pay the top price for an aquamarine that has a noticeable "window" in the center of the stone, that is poorly polished or unsymmetrical, or that is deficient even slightly in one or more of the features to
be expected in an aquamarine of maximum beauty and quality. On the other hand, if he knows gem values, he may be able to buy such stones to advantage and have them re-cut to his specifications.

Gems cut in the orient are often badly distorted in shape. When they are offered for sale and a comment is made about their poor symmetry, the reason advanced is usually, "there was a spot of color near one end of the rough and the cutter placed it near the culet so that the color would spread throughout the stone." It is true that if there is a color concentration near the culet, it will often appear to be evenly spread across the entire stone when viewed face up. However, by actual examination under immersion of quantities of such stones, it has been found that only a small percent actually have color concentrations near the culet. Thus it becomes readily apparent that they are cut in this manner for the purpose of obtaining greater weight from the rough. If an unsymmetrical stone actually does have a color spot near the culet, it is obvious that re-cutting to proper proportions would remove the spot and the stone
would lose much, if not all of its color. It is also evident that if the stone had been cut originally for beauty rather than for weight, a smaller and more symmetrically shaped stone would have been cut from the color area that is now near the culet of the unsymmetrical stone. The value of the unsymmetrical stone is no more than the current price of a properly proportioned stone cut from this colored area. The additional
weight retained seldom compensates for the beauty that is sacrificed by incorrect cutting.

Most phenomenal stones are also cut in a manner that adds nothing to their beauty but considerably to their weight. Unless a star sapphire is almost completely transparent, nothing is added to (and something may be subtracted from) its beauty by leaving a significant portion of its weight below the girdle. A fine quality 35-carat cat's-eye was recently examined in a laboratory in which the weight was equally distributed above and below the girdle. The price per carat was considerably reduced, because half of the total weight would not have been visible after the stone was mounted. The owner was planning to saw the stone in half in order to produce two cat's-eyes of equal quality and greater value. He reasoned, correctly that they would be more saleable because of better symmetry and because they would be easier to mount. Often the price per carat of a phenomenal stone does not take into account excess weight below the girdle. In addition, the sides of such stones are frequently so rounded and steep that it is virtually impossible to set them security. These disadvantages must always be considered.

With experience it is possible to judge the degree to which a lapidist has brought out the inherent beauty of a gemstone. In addition, the jeweler will be able to realize added profits through the purchase and re-cutting of poorly cut stones.