Grading & Pricing

The splendid iridescence of shimmering colors, rippling over their surface, makes the opal a mysterious, elegant stone that can be as costly as a diamond’ – Cartier ‘Cartier Royal High Jewelry and Precious Objects’ 2014

     Lightning Ridge black opal is the rarest, most precious, and most valuable form of opal. Its unique play of varying colors, brilliance, and pattern also make it the most difficult gem to judge. It cannot be commoditized just as any one work of art cannot be, because its appreciation varies with every individual who views it.

     However, the 4 valuation factors of body background, colour, brilliance and pattern provide a base system built upon their rarity in nature and their beauty, which provides a guide to ascertain the quality and thus relative value of an opal.

     Each factor has a different weight on the final price. Body background constitutes 15%, Colour 35%, Brilliance 25%, and Pattern 25%.Body Background

  Colour

While Opal is unique from any other colored gemstone, it is still a colored gemstone and so color is the most important element. Do not let an Opals’ multicolored appearance confuse you while grading and buying, focus on the prominent colors and then break down the quality of the color focusing on three factors: Color Type, Saturation, and Tone.

a) Color Type

This applies to the predominant color as you examine the face of the opal. Red is the most valuable, then orange, gold, green, and blue. Red is the most valuable because it is the rarest found when mining and is always in high demand from buyers. Blue colored opals are the most commonly found in Lightning Ridge and thus have a lower price per carat. However, this does not subtract from their beauty as some can be stunning and more desirable to the consumer.

b) Color Saturation

Saturation is the term for the strength or luster of the color. If you look at the opal from a distance and the color is jumping out at you then it has a high saturation. Conversely, if you are holding it in your hand and the color appears dull or weak then it has a low saturation.

c) Color Tone

Tone refers to the relative lightness or darkness of the color type. Tone can be referred as light, medium-light, medium, medium-dark, and dark. Ideally you would like a tone that ranges from medium-light to medium-dark as they are the most favorable.

Body Background

The darkness of a black opal is determined by the tone of the background of the stone. Top rating for darkness might be the black of a midnight sky, and, as the background tone decreases until it is a light colour, so does the relative value of the stone.

Cut

A good cut in opal is one that lets the potential beauty of the gemstone be displayed optimally. Opal does not need to be faceted as its beauty is present without aid. the rough has traditionally lent it to be cut into cabochon ovals, although all types of shaped cuts are possible.

When examining the cut it is important to note several factors:

• that the color is faced towards you as well as possible
• the gemstone has balance. There is no disproportion in the width, length, or depth of the shape.
• the higher the cabochon or dome the higher the price per carat
• that there is no excessive weight in the back of the opal that results in a higher total price per carat
• the cut has resulted into a colorless window that allows you to see through the gemstone

A free-form sap cause a reduction in value because to the excess weight it gives the opal. the amount of value deducted depends on the added weight given in the cutting. Some free-form cuts can be very artistic and require high amounts of skill and imagination to execute, and can maintain a high value and provide an opportunity for a unique piece of jewelry.

Multipliers

Pattern

A multicolored pattern is unique to opal. If the pattern captivates you then it gets a higher valuation. The broader patterns generally attain higher values.

The rarest and most highly prized of the name patterns is the harlequin pattern. A true harlequin pattern on a gem quality opal is extremely rare, and so will multiply the price significantly.

Other noted patterns are chaff, chinese writing, floral, straw, mackerel, ribbon, rolling flash, flagstone, and broad flash. Each will result in a multiplication of the opals’ value depending on how fine the pattern.

All-Lighting

An opal will attain a higher value if it looks equally good in sunlight, as opposed to artificial light, and shade.

Deductions

Inclusions, fissures, fractures, and common opal

When an opal forms it can have additional elements within the rough that effect the visual purity of the gemstone. A typical inclusion might be a small piece of clay in the face of the opal

A small inclusion not visible to the naked eye may have little if any effect on the price per carat. A larger inclusion located in the center of the face of an opal can have a more significant effect on value. It is important to note that some inclusions do not detract from the value of an opal and are accepted as part the natural beauty of an opal, as well as providing a visual indicator of its long geological history.

Common opal with elements of carbon and manganese than silica can form lines in the opal that separate the color plates or move within the color plates. These are not inclusions, although they look like them, but can result in decreased value depending on their prominence.

Fissures and fractures are a natural part of opal just as they are any other gemstone. Noticeable fractures in an opal that effect the visual appeal of it will cause a deduction in value.

As a rough guide an opals value is reduced if certain factors exist:

• The flatter the surface of the stone the less value it will have.
• If it doesn’t look equally good in all lighting – sunlight, artificial light, and the shade.
• If it has intrusive potch lines that interfere with the pattern and play of colour.
• If it has excessive sand in the background
• If it has excessive potch on the back of the stone that adds to the carat weight
• If the stone has a window where no colour appears on the face of the stone.
• If it is an off shape or free form