John M. King

A Contribution to Understanding the Effect of Blue Fluorescence on the Appearance of Diamonds

GEMS & GEMOLOGY Winter 1997 any factors influence the color appearance of colorless to faint yellow diamonds. Typically, such diamonds are quality graded for the absence of color according to the D-to-Z scale developed by the Gemological Institute of America in the 1940s (Shipley and Liddicoat, 1941). By color appearance, however, we mean the overall look of a polished diamond’s color that results from a combination of factors such as bodycolor, shape, size, cutting proportions, and the position and lighting in which it is viewed. When exposed to invisible ultraviolet (UV) radiation, some diamonds emit visible light, which is termed fluorescence (figure 1). This UV fluorescence arises from submicroscopic structures in diamonds. Various colors of fluorescence in diamond are known, but blue is by far the most common. The response of a diamond to the concentrated radiation of an ultraviolet lamp is mentioned as an identifying characteristic (rather than a grading factor) on quality-grading reports issued by most gem-testing laboratories. Other light sources—such as sunlight or fluorescent tubes—also contain varying amounts of UV radiation. Although there have been instances where the color and strength of the fluorescence seen in diamonds observed in these other light sources are also believed to influence color appearance, in recent years the fluorescence noted on grading reports has been singled out by many in the diamond trade and applied across the board as a marker for pricing distinctions. Generally, these distinctions are applied in the direction of lower offering prices for colorless and near-colorless diamonds that exhibit fluorescence to a UV lamp (Manny Gordon, pers. comm., 1997). Other trade members contend that the overall color appearance of a diamond typically is not adversely affected by this property (William Goldberg, pers. comm., 1997); many even say that blue fluorescence enhances color appearance. A CONTRIBUTION TO UNDERSTANDING THE EFFECT OF BLUE FLUORESCENCE ON THE APPEARANCE OF DIAMONDS

THE WITTELSBACH-GRAFF AND HOPE DIAMONDS: NOT CUT FROM THE SAME ROUGH

1749, but was stolen in 1792 during the French Revolution. Twenty years later, a 45.52 ct blue diamond appeared for sale in London and eventually became part of the collection of Henry Philip Hope. Recent computer modeling studies have established that the Hope diamond was cut from the French Blue, presumably to disguise its identity after the theft (Attaway, 2005; Farges et al., 2009; Sucher et al., 2010). For a thorough look at the history of the Hope diamond, see Patch (1976), Morel (1988), and Kurin (2006), along with the references cited above. The first reliable record of the Wittelsbach Blue diamond dates to 1673 in Vienna, when it was listed as part of the estate of Empress Margarita Teresa of Austria. As with the Hope diamond, its exact source in India is unknown, though the Kollur mine has been mentioned (e.g., Balfour, 2009). The stone passed from the Hapsburg court to the Bavarian Wittelsbach family in 1722 as part of a dowry, and it remained in the Bavarian crown jewels until the THE WITTELSBACH-GRAFF AND HOPE DIAMONDS: NOT CUT FROM THE SAME ROUGH

An Important Exhibition of Seven Rare Gem Diamonds

Splendor of Diamonds,” a collection of unique gem diamonds, is on temporary display at the National Museum of Natural History (NMNH) at the Smithsonian Institution inWashington, DC (see figure 1). This museum is the home of the U.S. national gemstone collection, and is where the famous 45.52 ct blue Hope diamond has resided since its donation by Harry Winston in 1958. Since its renovation in 1997, the Harry Winston Gallery in the Janet Annenberg Hooker Hall of Geology, Gems, and Minerals has been one of the most popular sites in the museum. Typically around two to three million people visit this hall every summer (J. E. Post, pers. comm., 2003). On only one other occasion has another important diamond been displayed in the same room; this was the historic 41 ct Dresden green diamond, which was exhibited on a rare loan from the Green Vaults in Dresden, Germany, in October 2000 (“Harry Winston . . .,” 2000). The exhibition of these seven diamonds in the same setting attests to the rarity of this special collection. “The Splendor of Diamonds” at the NMNH includes the 203.04 ct colorless De Beers Millennium Star as well as six exceptional diamonds that represent some of the rarest of naturally occurring colors. On the initiative of GIA representatives and with the sponsorship of the Steinmetz Group, the seven diamonds were brought together from private collections throughout the world. Each is unique in its combination of size, color, and quality. Over the years, GIA staff members have examined many important gemstones as part of our laboratory grading services and for research purposes. These opportunities have allowed us to characterize and document the gemological properties of a number of unique diamonds in public and private collections that would otherwise not be available for gemological study. Fryer and Koivula (1986, p. 102), in their account of the examination of four important gemstones on public display for a limited time (the Star of Bombay sapphire, the Portuguese diamond, and the Marie Antoinette diamond earrings), concluded with this statement: “We hope that our examinations will provide a more complete record

Color Grading "D-to-Z" Diamonds at the GIA Laboratory

brilliant diamond of VS1 clarity was about 16% in both Idex and Rapaport. As part of its educational program, GIA has taught the basics of color grading D-to-Z diamonds since the early 1950s. And in the more than five decades since the GIA Laboratory issued its first diamond grading report in 1955 (Shuster, 2003), it has issued reports for millions of diamonds using the D-to-Z system. Throughout this period, GIA has experienced increased demand for its diamond grading services over a growing range of diamond sizes, cutting styles, and color appearances. This has required a continual evolution in the equipment and methods used in the GIA Laboratory, while maintaining the integrity of the grading system itself. At the core of the system’s development has been an ongoing assessment of how best to observe a diamond in order to describe its color consistently. At times, the resulting adjustments have appeared to conflict with earlier statements. This article reviews the history of the system’s COLOR GRADING “D-TO-Z” DIAMONDS AT THE GIA LABORATORY

The Impact of Internal Whitish and Reflective Graining on the Clarity Grading of D-to-Z Color Diamonds at the GIA Laboratory

diamond clarity grading is the impact of graining, especially internal “whitish” or “reflective” graining (see, e.g., figure 1). R. E. Kane’s 1980 Gems & Gemology article, “The Elusive Nature of Graining in Gem Quality Diamonds,” gave the reader an overview of the causes of graining, illustrated the range of appearances associated with it, and generally outlined its relationship to clarity grading at the GIA Laboratory (see also Kane, 1982). The present article looks at this subject 25 years—and literally millions of diamonds— later. For the purposes of diamond grading, graining refers to optical discontinuities that are observable with a 10× loupe or a standard gemological microscope. The overall transparency of a diamond can be affected by these discontinuities to varying extent. While fractures and cleavages are also discontinuities, an important difference is that with graining no open space (i.e., air/diamond interface) is present. Whitish graining can be classified into banded, tatami, and overall haziness, whereas reflective graining typically consists of internal reflective planes. Many of the forms graining takes (e.g., surface lines or colored bands) are readily observed, and their relationship to clarity can be understood with standard diamond grading conditions and criteria (i.e., ease of visibility at 10× magnification and location). But whitish graining and reflective graining are often more difficult to distinguish and relate to clarity, since their visibility is influenced more by optical factors such as the type of lighting and the angles of observation in relation to the lighting.