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Opal Industry Nomenclature
Over the past few years the Gemmological Association of Australia (GAA) has worked at developing a defining nomenclature (that is descriptive naming system) for Opal through a specialised subcommittee chaired by Anthony Smallwood FGAA, GG. After broad industry wide consultations, the following Opal nomenclature system has been developed and is reproduced here with the kind permission of the GAA. The Opal Association strongly endorses the use of these definitions with the aim of standardising nomenclature across the opal industry worldwide.
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OPAL CATEGORIES
Opals can be broadly categorized into several types, with the most common being precious opal and common opal. Precious opal is characterized by its ability to diffract light, resulting in a spectrum of colors that can shift and change depending on the angle of view. Common opal, on the other hand, lacks this play-of-color and is typically opaque or translucent.
precious opal
Within the category of precious opal, there are further classifications based on body tone. Body tone refers to the overall color of the opal when viewed in transmitted light. The body tone is graded on a scale from N1 to N9, where N1 represents a black opal and N9 represents a white opal. Black opals are highly sought after due to their dark background, which enhances the vibrancy of the colors displayed. In contrast, white opals, while still beautiful, tend to have a lighter appearance and may exhibit less intense color play.
transparency
Another important classification is based on the opal's transparency. Opals can be categorized as transparent, translucent, or opaque. Transparent opals allow light to pass through, showcasing their internal structure and colors. Translucent opals permit some light to pass through but are not completely clear, while opaque opals do not allow light to penetrate, resulting in a solid color appearance.
Opalescence is another characteristic that can influence classification. This phenomenon occurs when the opal exhibits a shifting play of color, often described as a "fire" effect. Opals with strong opalescence are typically more valuable, as they display a broader range of colors and a more dynamic visual experience.
In addition to these classifications, opals can also be categorized based on their origin. Australian opals are among the most famous, particularly those from regions such as Coober Pedy and Lightning Ridge. Other notable sources include Ethiopian opals, which are known for their unique color patterns and clarity, and Mexican opals, which often exhibit a distinctive orange or red hue.
In conclusion, the classification of opals is a multifaceted process that considers various physical attributes, including body tone, transparency, opalescence, and origin. Understanding these classifications not only enhances appreciation for these gemstones but also aids in making informed decisions for collectors and buyers in the market.
