OPAL SECTION Opal gemstone Grading.
Australian Opal body tone scale:BLACK OPAL .N1 JET BLACK & N2 VERY SIMILAR as black as the background of this website. N3 SIGNIFICANTLY LIGHTER BLACK in colour.N4 DARK OPAL N5 IS RECOGNISED AS DARK OPAL BUT WILL HAVE A GREY BACK TO THE OPAL STONE.N6 IS LOSING ITS DARK BACK. N7 LIGHT OPAL N8 very like grey N9 white background of the Opal gemstone.
The following grading criteria are described in Opal Identification & Value by Paul B. Downing, Ph.D. and are based on the grading system developed by the Lightning Ridge Miners Association in collaboration with several Australian gem industry organizations. I myself recommend this Australian formula as I have mined opals around lightning Ridge for for 35 years I have been a member of the lightning Ridge mining Association , and I remember Mr Dowling as a master Opal cutter and even in recent times his Opal jewelry business at Harvey Bay Queensland in 2008. In recent years I have been extensively involved in Opal gemstone Retail and wholesale marketing as well. Members of the lightning Ridge miners Association New South Wales Australia can have some loose Opal gemstones priced free of charge,I would highly recommend also becoming a member.
The term base color is a bit complicated because it actually includes three characteristics: color, tone andclarity. Color is the hue of the body plus the tone based on the Lightning Ridge Miners Association Tone Scale. Dark base colors are black, semi-black and grey. There are also red, orange, yellow, blue, green and brown base colors. Clarity refers to the degree of transparency, from transparent (crystal) through translucent (semi-crystal) to opaque.
Brightness of fire
The major factor in determining an opal’s value is its brightness of fire, which is graded as Faint, Dim, Somewhat Bright, Bright, Quite Bright, Extremely Bright or Brilliant. The higher the brightness level, the more valuable the opal will be.
An opal’s cut is important because it not only affects the beauty of opal, but its durability. Most opals are cuten cabochon, or without facets. Many are oval, but they can be cut to nearly any shape, or free-form. An opal should be cut thick enough to not be subject to breakage, but not excessively thick so as to be unattractive. Pay close attention to cut when purchasing loose opals. A stone that is too thick or too thin may be difficult to set properly. The surface should be smooth and all edges should be beveled or rounded to protect the stone from chipping during setting.
Inclusions in opals
Opal inclusions are graded differently than those in other gemstones. Inclusions that don’t detract from the beauty of the stone are frequently ignored. Cracks and crazing, however, severely affect value, because they affect both the beauty and durability of the stone.
Most opals are sold on a price per carat basis like other gemstones, but boulder opal is generally priced by the piece since the ironstone matrix is so heavy.
Just like base color, fire color has three components: hue, lightness or tone, and saturation. These terms have the same meanings as when applied to colored gemstones. Hue refers to the fire’s color There will always be a dominant color and usually a secondary color For example, a stone can have one fire color, say, blue. If a stone has a dominant blue and secondary green, it has a blue-green fire. If it has other strong fire colors, it is a blue-green multicolor. Red fire is generally the most valued color Lightness or tone refers to the degree of black cast in the hue, and saturation refers to the intensity of the fire. Saturation can be Dull, Average or Vivid.
Opals are natural materials and will never be perfectly consistent in color, brightness, or pattern of fire, or in density of background color. The higher the degree of consistency, the more valuable the opal.
An opal that is consistently bright when viewed from any angle is more valuable than one that appears brighter from some angles than others. However, an opal with such strong directionality that it is unsuitable for a ring stone may make a beautiful pendant.
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