Every opal is a unique and unrepeatable gem. Starting from this premise, it's not easy to create a precise order for classifying and valuing opals. Many factors contribute to classifying, evaluating, and pricing opal, an extremely diverse and elusive gem whose saturation, play of color, and pattern, as well as brilliance, transparency, and tone, can confuse even the most expert observer. Over time, many miners have developed a local terminology, which, however, has prevented gemologists from formulating a precise classification. Even following these guidelines, one finds oneself tangled in a tangle of unclear rules. Over the years, however, at least a partial cataloging of precious opals has been achieved, classifying them based on the following certain characteristics that contribute to determining the opal's value:
1. Type of opal
2. Body tone
3. Transparency
4. Play of colors
5. Brilliance
6. Patterns or drawings
7. Cutting
After careful consideration, in order to provide consistent and clear information to its customers, Opalemio has decided to consider only these parameters commonly accepted by Anglo-Saxon opal experts in the opal world in its store's opal descriptions, avoiding the entire chain of local and individual interpretations that only lead to confusion. We are confident that this information will help you better understand and appreciate the opals you are interested in and the reasons for their value.
TYPE OF OPAL
Solid opal is basically divided into three types:
Solid Type 1 - The entire gem is composed homogeneously of opal, which can be either precious opal with play-of-color or common opal without color (potch).
Solid type 2 - A layer of precious or common opal adheres to host rock of a different chemical composition. This type of opal is commonly called boulder opal.
Solid type 3 - Precious opal that is found in fractures and pores of the host rock and appears as flakes and veins that sometimes create striking patterns (Koroit or Yowah Nut). This type of opal is called Matrix opal.
BODY TONE
The body tone of an opal refers to the relative darkness of the opal's background. Simply put, to determine the tone, the observer focuses not so much on the colors or the pattern as on the gem's background, which can be white (N9) or, through various shades of gray, all the way to black (N1).
From N1 to N4 - Black Opal - (Black opal) Category of opals that shows a play of colors on a background that goes from black (the rarest and most valuable N1) to dark gray (N4).
N5 to N6 - Gray or Dark Opal - (Dark Opal) A type of opal that displays a play of color on a dark or gray background. This category is sometimes also called semi-black.
N7 to N8 - Light Opals A category of opals that shows a play of color on a light or pale gray background.
N9 - White Opals Opals showing a play of color on a milky white background.
TRANSPARENCY
Precious opal can present all shades of transparency, from transparent to semi-transparent (translucent) to opaque. The tone scale applies only to opaque opals; crystal opals, which are transparent or semi-transparent, do not fall into any of these categories, as their background tone is influenced by the surface on which they are placed.
GAME OF COLORS
The unique characteristic of opal is the presence of different colors within the gem. Starting from the primary hues of the color wheel, opal can range across thousands of shades and hues from the infinite list of colors. The general rule is that the more colors, the higher the value of the stone. Furthermore, the presence of rarer colors, such as red in Australian opal and blue in Ethiopian opal, increases its value exponentially. So, for example, given the same tone, carat weight, brilliance, and cut, an Australian opal with various shades of blue will be less valuable than an opal with blue and green, which in turn will be less valuable than a gem with a play of blue, green, and yellow, and so on. If red is also present, then the quality is top-notch.
BRILLIANCE
The brightness or brilliance of the colors is a fundamental factor that helps determine the value of opal. A very bright opal, however small, has a significantly higher value than a very large one with low brightness. Opalemio currently uses the commonly accepted brilliance scale in Australia, which consists of seven levels from B1 to B7.
B 7 - Very faint - The opal shows hints of color only in sunlight.
B 6 - Weak - The opal shows a faint play of color under both sunlight and artificial lamplight.
B 5 - Low brightness - Opal shows a certain play of colors both under sunlight and under artificial lamplight.
B 4 - Bright - Opal displays a beautiful play of color in both sunlight and artificial light. It displays no color when placed in the shade away from the light.
B 3 - Very bright - The opal displays a beautiful play of colors under dim artificial light and very good sunlight. When placed in the shade, the colors become more noticeable.
B 2 - Brilliant - Opal has an intense play of color under both artificial and sunlight and remains very bright when viewed in dim light.
B 1 - Exceptionally Brilliant - Opal has a vivid play of color and electric highlights in any light and is even brighter when viewed in dim light.
Which of these brilliance levels does my opal fall into?
Pick up your opal around noon on a clear day with a beautiful blue sky and bring it into the shade of your home, facing north. You can then determine the brilliance of your gem by measuring the play of color you observe with the seven levels of brilliance. Simple, right?
PATTERNS OR DRAWINGS
This English term applied to opal indicates the ornamental design of its surface, the geometric repetition of a motif. Patterns are a very important aspect in evaluation and in nature they are found in such variety only in opals. Below is a list of the most well-known patterns: (taken from the book "Rediscovering Opals in Australia" by Stephen Aracic):
Harlequin : This is certainly at the top of the list and is the most valuable of all the luminous opal patterns. This rarity features shimmering patches of varying shapes, from rounded to slightly square, a colorful, ever-changing array of colors reminiscent of the patches on the Harlequin mask's costume. See more
Ribbon : A play of colors resembling ribbons, both wavy and in straight lines.
Pinfire : features a surface dotted with pinhead-sized dots, the most obvious visible from a single direction, which vary in color from different angles.
Stardust : It features a myriad of dots in a thousand shades, similar to stardust.
Flag : The colors are arranged to form a triangular-shaped flagstone, some resembling fish scales.
Chinese writing : rare and valuable design where the colors form a pattern similar to Chinese writing characters.
Chaff : features colors in segments resembling chopped straw or in multiple lines placed parallel to each other.
Mackarel sunset : features a whole range of colors in moving streaks, similar to clouds at sunset.
Butterfly : The colors are arranged to form patterns similar to the patterns on butterfly wings.
Mossy : coloured, moss-effect flecked shine.
Floral : A showy effect similar to flowers in a bouquet, very common in Queensland opals.
Rolling flash : Bright colors oscillate from one side of the opal's surface to the other, sometimes with chatoyancy.
Star : Six-pointed star effect waving on the surface, very rare.
Rainbow : the colors are arranged in a rainbow.
CUT
The shape or cut also determines an opal's final valuation. For example, a regular and symmetrical shape, such as oval, teardrop, or cushion, is more valuable than a prolate or irregular and asymmetrical shape. Furthermore, a cabochon opal, that is, a thick oval shape, is more valuable the thicker it is and the more regular its curvature from base to tip.
