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.