World Of Gems Conference 2017 Proceedings Book

WORLD OF GEMS CONFERENCE V - 14 - SEPTEMBER 2017 nificantly the behavior of the light path through the stone and the resulting effects (Figure 2). Jadeite can often be differentiated from other jade-like gem materials by the presence of the “cui” (Cantonese) or “tsui” (Mandarin) effect. The “tsui” is produced by diffraction of light in a shallow area below the stone’s surface; if clearly visible, it is part of the characteristic crispy luster of jadeite. But, the finest qualities, especially the best “imperial jade” additionally produce an internal shine known as “ying” (Figures 2 and 3). This internal glow, which considerably increases beauty and value of jadeite is produced by light that penetrates deeper into the translucent to sub-transparent jadeite, where it is scattered by the fine granular texture. “Ying” means hero, outstanding, or outstanding person in Chinese; in this context, it stands for outstanding qualities in jadeite. The ying-effect is best observed perpendicu- lar to the light source, in peripheral areas of well- shaped cabochons with good proportions and convex bottom part, or in beads. Thus, the prerequi- sites for this highly desirable effect are a high quality fine-grained base with a compact and even texture, a high degree of diaphaneity, and a very good polish. The ying-effect and the color intensity are the main reasons why very high-quality jadeite should not ex- ceed a certain size; this size corresponds to the max- imum size the material being cut is still able to show the ying-effect without having its center darkened by a color that is so intense that it hinders translucency. In “imperial jade” beads of exceptional qual- ity, this size is approximately 18 mm. In jadeite items of high value, the transparency has a significantly stronger influence on the value than color. When assessing the “purity” of jadeite, it should be differentiated between “clarity” and “cracks.” Clarity accounts for the pres- ence or absence of inclusions such as “pol- lens,” dark mineral grains, and visible micro-shear zones. Note that blemishes that have been attributed to the texture quality should be disregarded during the clarity as- sessment. If fissures or fractures are pres- ent, whether open or healed, they should be judged separately because they can dramat- ically reduce the value of a jadeite item, and worse, making it factually unsellable. Blem- ishes that have been attributed to the texture quality should be disregarded during the clar- ity assessment. In jadeite, ductile micro-shear zones or micro- shear bands are internal textural features that were caused at comparatively great depth during the stone’s formation by shear stress, a lateral stress which caused tear- ing and smearing in the stone’s body. Shearing is part of the gemstone-quality jadeite’s formation where plasticity pre- vents fracturing; the material experiences high degree of de- formation, reducing its grain size and interstitial spaces, and imposing a distinct preferred orientation. Despite micro-shear zones in jadeite generally resemble healed fissures or healed JADES OF BURMA FIGURE 2. FIGuRE 3. Ying-effect in a jadeite bead.