:: SUWA/Dictionary-Gemstones,Quality and Value::

6. DEFECTS IN GEMSTONES

The determination of beauty and tone are important points in judging the quality of gemstones. The quality scales used in this book are arranged with beauty along the horizontal axis and tone on the vertical axis.

Tone is divided into levels ranging from 7 to 1, with 7 being “dark”, 5 “medium”, 3 “light”, and 1 “extremely light”. Data from spectrophotometric readings were sampled, and the final tone levels were established visually. Whereas the beauty scale represents a complex combination of a variety of factors, tone is a linear scale dealing with just one factor.

Color can be thought of as being comprised of three components: hue, which is represented by the basic color sensations of red, orange, yellow, green, blue, and violet-such as the red of ruby, the yellow of citrine, or the blue of sapphire; saturation, which indicated whether a color is a beautiful pure color, and the degree of gray or brown overtones present; and tone, which describes the color’s level of lightness or darkness.

Professional will always inspect a gemstone using a 10-power loupe. Examining the stone for distracting defects such as inclusions that adversely affect durability or appearance, as well as the quality of finish, they decide whether it meets their standards, or if they should repolish the stone and use it in jewelry. Here is where each manufacture and stone establishes its character, and where differences in the quality of jewelry originate.

A friend of mine who is a diamond cutter in Antwerp gave his wife a gift of a five- carat, SI1 diamond. It was much less expensive than a flawless diamond (free of internal and external imperfections at 10x).

Some might say that he bought this diamond just for its impressive size, but that was not the case. A five-carat SI1 can show fairly large imperfections under 10x magnification, but this diamond only contained a transparent crystal inclusion, invisible to the unaided eye. As a matter of fact, the inclusion was an important proof of the diamond’s natural origin. Should synthetic diamonds become common in the marketplace, inclusions that provide proof of natural origin will be appreciated and valued, provided they do not detract from beauty. They might even command a premium.

On the other hand, the presence of cleavage in the girdle area of a diamond would be a serious defect. There is the possibility that such cleavage may cause a stone to chip during the setting process, or that the stone may break while being worn if it is forcibly struck in certain directions. It is important that even if such a stone were graded as SI1, its essential value would be totally different from that of the SI1 diamond my friend gave to his wife. That SI1 diamond, because of its balance of high transparency, brilliance, dispersion, scintillation, and pleasing appearance (as well as its reasonable price), was a truly satisfying stone-which is precisely why such an expert among experts would purchase it.

A diamond grading report is similar to a health examination, in that the same results would mean different things to a young person, a middle-aged person, and an old person. The physician determines whether or not the results pose a problem for each individual patient. In the same manner, a gem dealer must decide on a case-by-case basis if something represents a problem-free imperfection or a defect. A conscientious gem dealer will stubbornly adhere to personally established quality standards, such as not hiding inclusions beneath prongs even if they aren’t eye-visible, and not using gemstones with eye-visible dark inclusions in jewelry. In Japan, particular importance is attached to diamond grading reports, but the essence of gemstone value cannot be determined just from analysis of the information contained therein.

Fracture filling is not only done to emeralds, but also to low-quality faceted rubies, a number of cabochon-cut gems and low-quality diamonds (via lead-based glass impregnation). If the filling material (such as oil) comes out of a heavily treated stone, the stone will revert to its former unbearable appearance, so it is best to avoid items that have undergone such treatment.

The photographs to the lower right on the next page show Mong Hsu rubies with abrasions on the junctions between the table and crown facets. This type of poor finish is not tolerated in carefully manufactured jewelry. (Even if well-finished material, heat-treated Mong Hsu ruby suffers a decline in toughness due to the high-temperature heating process.) If jewelry is stoned or worn carelessly, stones may become scratched as they rub against each other. Precautions should be taken to avoid this. The first ruby shown is a well-finished gemstone with sharp facet junctions. As evidenced by the fact that rhodolite, is more easily scratched than aquamarine, the ability to withstand wear varies between the different gemstone types.

When accepting merchandise from a customer, a jeweler should properly plot the stone (record the type of inclusions present on a diagram) to provide a means of confirming the stone’s identity when it is returned. There are no problems in most cases, but plotting the stone enables the clarification of any misunderstandings that may arise. Rather than associating a company’s merchandise with imperfections, a plot accompanied by a clear, positive explanation that imperfections can serve as proof of natural origin will be an appealing testimony to the wonder of gemstones.

Expert jewelers need to concern themselves with issues such as the color fading of natural padparadscha sapphire and blue zircon, or the fact that the fracture-filling of emeralds poses problems with recutting and changes in appearance over the ling term. Both consumers and professionals alike can judge the beauty and tone of gemstones, but deciding whether inclusions and treatments pose problems or not is the expert’s domain. The Gemological Institute of America (GI’A) teachers a common language and methods of quality analysis in the field of gemology, and is working to spread that knowledge. The hope is that the Institute’s graduate gemologists will enter the industry and, through practical experience, mature into jewelers capable of judging beauty and distinguishing between simple imperfections and serious defects. A gemstone that is confirmed by a professional to be beautiful and free of durability-threatening imperfections is one that can be confidently recommended to anyone.

Index