The more you look at them, the more they have to offer-the more you will see. Additionally, the flow structures give rise to unusual patterns that can resemble blades of grass, sections of ribbon, branches, or sharp blades. When cut properly, often paralleling the flow structure in the glass, the optical effect is both sudden and stunning. 551–557)-which means that stones must not be polished to such an extent that the color spectrum is removed. Ma et al., “The origin of color in ‘fire’ obsidian,” Canadian Mineralogist, Vol. There must be two overlying layers that have a different refractive index, which produces this remarkable iridescence.”ĭodge also noted that the flow bands of obsidian that exhibit color are very thin-between 300 and 700 nm (C. And if you move the stone or change the angle of the light, some areas of that stone will reveal or change the perceived colors. So when those two reflected portions of light come back to your eye, you’ll see red, you’ll see green. “This phenomenon resembles the color effect you see in soap bubbles, oil on water, or windshield wiper fluid in contact with the windshield. This contact zone interacts with light as light reflects from the surface, enters the material, and is in part bent due to the optical characteristics of glass-its angle of refraction,” said Dodge. “This is caused by a thin-film interference, when one type of the obsidian is in contact with another type of obsidian, such as an iron-rich obsidian. Impurities in the glass such as magnetite (an iron oxide) or manganese give the material its natural bodycolor.īeyond the bodycolor, though, it is the sudden flashes of vivid iridescent colors that give fire obsidian its distinctive appeal. Obsidian typically appears black or brown and is generally translucent in smaller pieces. Ma et al., “Micro-analytical study of the optical properties of rainbow and sheen obsidian,” Canadian Mineralogist, Vol. Much of that material comes from the Mexican state of Jalisco and from northern California (C. But only a tiny percentage of it is suitable for fire obsidian.ĭodge differentiates fire obsidian from so-called rainbow (or sheen) obsidian, which exhibits broad, mostly even bands of pastel colors. A rhyolitic dome field, Glass Buttes has vast quantities of obsidian in various patterns and varieties. In North America, Mexico, and South America, there is an abundance.”įire obsidian, so named for its vivid spectrum of colors, is rare and so far has been found in only one site within the Glass Buttes region of central Oregon. Most of it comes from the Western United States, but anywhere there are volcanic terrains. “The material is widespread across the world. “Obsidian, a natural volcanic glass, is not particularly rare,” Dodge said, demonstrating how to shine a light on samples of his most vibrant cabochons. While the exterior shapes he produces are large oval cabochons or tablets, the patterns and colors experienced in any piece, with proper lighting and orientation, are never replicated. He uses diamond abrasive cabochon-cutting equipment and optical-grade cerium oxide polishing powder to reveal vivid spectrums of undulating color and depth. Others contain reflective layers that are not flat-when fashioned, they appear to billow and ripple like a wind-blown flag.ĭue to these nuances, which change from sample to sample, he takes time to carefully trim, fashion, and polish the pieces. Interviewed at his lapidary studio in Phoenix in 2022, Dodge noted that even among his carefully selected chunks of glass, there are countless samples that simply do not show the effect, even after lapidary work. Although it is challenging to visualize where the colors may lie in the rough, he has developed an affinity for locating iridescence in the raw material (figure 3). Photo by Pedro Padua.ĭodge has spent years learning how to best fashion the material, first forming and then delicately polishing the glass at his lapidary workshop in Phoenix, Arizona. The flow bands give rise to the phenomenal colors, and provide guidance in his lapidary work. This provides a “window” into the stone so he can spot flow bands in the glass. Dodge describes taking a chip off of the rough. Applied Jewelry Professional ™ Online Diplomaįigure 3.
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