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- Title
Photographing Phenomenal Gemstones.
- Authors
Weldon, Robert
- Abstract
Phenomenal gemstones pose unique challenges to gemologists. Chief among them is how to best light the gems to reveal their optical characteristics, such as chatoyancy, asterism, play-of-color, color change, iridescence (see figure), schiller effect, and labradorescence. Lighting the gem for photography parallels the actions taken by a gemologist to observe such phenomena. Lighting is the most important aspect to consider when photographing phenomenal gems. With chatoyancy or asterism, the direction and intensity of the light source are crucial. Whether a light source is diffuse, or pinpointed and direct, also plays a role. A traditional three-point lighting system (in which gems are back- and side-lit) is not used for chatoyant or asteriated gems because the various light sources may cause phenomenal effects to appear in unintended parts of the gem. Even if side lighting is diffused, distracting reflections appear in cabochon-cut gemstones. Photographers prefer to rely on a single light source, aimed perpendicular to the convex top of the cabochon, to bring out asterism and chatoyancy. A light source's color temperature is also important to render the correct color balance in photographs of gems and minerals. With digital photography, this adjustment can be corrected "in-camera." Color-change phenomena in gems are observed under specific lighting color temperatures. However, in both digital and film photography, capturing accurate color change under various lighting conditions is not as straightforward; in many cases "corrections" are made with direct observation and photo-editing software. Not all phenomenal gemstones of a particular type require similar lighting. To observe play-of-color in opal, direct, pinpoint lighting is often thought to be ideal, but that is not always true. Some opals are successfully lit, and their play-of-color displayed, with diffused light---or with a combination of direct and diffused light. Phenomenal feldspars, such as moonstone, sunstone and labradorite, require diffused illumination to exhibit the phenomena. In moonstones, diffused lighting, as well as the physical orientation of the gem, allows the photographer to judge where the gem's adularescence appears strongest (i.e., its photogenic angle). Adularescence is most obvious when a moonstone is photographed against a dark background. Copper platelet inclusions in American sunstones, which cause the schiller effect, may reflect too strongly with direct lighting, creating hot spots. In such cases, the gem may need to be tilted, or the camera angle changed, so that a plane of inclusions is softly illuminated. The goal is to illuminate the inclusions to show moderate-to-strong relief and sharp detail.
- Subjects
GEMS &; precious stones; ASTERISM (Crystallography); COLOR; LIGHT sources; LIGHTING; FELDSPAR
- Publication
Gems & Gemology, 2006, Vol 42, Issue 3, p144
- ISSN
0016-626X
- Publication type
Article