Factor 1: brightness of play-of-colour
Brightness is the most immediately important quality factor in opal. A stone with vivid, brilliant colour play that is clearly visible across the room is more valuable than a stone that requires close examination or special lighting to show any colour. The Australian opal trade uses brightness grades from B1 (brilliant, visible at arm's length in normal light) through B5 (faint, only visible under directed light close to the stone). B1 brightness is the standard for fine quality (Wise, 2016; Australian Opal Centre; GIA).
Brightness assessment is done under standard diffuse daylight or daylight-equivalent illumination, not under concentrated spotlight. Many stones that appear brilliant under a strong spotlight reveal only moderate brightness in normal diffuse lighting. The diffuse lighting test is the relevant one for jewellery wear.
Factor 2: spectral colour range
The spectral range of colours visible in the play-of-colour determines a significant portion of value. The colour hierarchy from most to least valued: red is the rarest and most prized because it requires the largest silica sphere spacing and is produced by the highest-energy diffracted wavelength. A stone showing vivid red in its play-of-colour is immediately in a premium tier. Orange and yellow are the next rarest. Green is the most common play colour. Blue and violet are common (GIA; Wise, 2016, pp. 203–204).
Opal spectral colour value hierarchy. Red is the rarest play colour (requires the largest silica sphere spacing) and commands the highest premium. A stone showing red in its play-of-colour is immediately in a premium category. Violet and blue are the most common play colours. Source: GIA; Wise (2016).
Factor 3: body tone
Body tone is the background colour of the opal independent of the play-of-colour. The industry standard is the N-scale (Neutral scale) running from N1 (jet black) to N9 (white). Darker body tones (N1–N4) produce higher contrast for the play-of-colour, making the spectral colours appear more vivid and brilliant. This is why black opal commands premiums over white opal with equivalent quality play-of-colour: the dark background acts as a contrast enhancement (GIA; Australian Opal Centre grading).
N1 (black): the finest Lightning Ridge material; jet black body. N2–N3: very dark grey to dark grey; still qualifies as black opal under most grading standards. N4–N5: medium grey; boulder opal often in this range. N6–N7: light grey to light; white opal lower end. N8–N9: white; commercial white opal standard.
Factor 4: pattern types
The pattern of the play-of-colour refers to the spatial arrangement and movement of the colour flash. From highest to lowest commercial value:
Harlequin (or flagstone): Large, angular patches of colour arranged in a mosaic pattern resembling a harlequin diamond pattern or irregular flagstones. The rarest and most prized pattern; fine harlequin pattern Lightning Ridge black opal is among the most valuable opals in existence. True harlequin is uncommon even in Lightning Ridge material.
Rolling flash: A broad band of colour that "rolls" across the stone as the viewing angle changes. Vivid and dramatic in person; commands strong premiums.
Broad flash: Large areas of vivid colour that are relatively stable across moderate viewing angle changes. Very commercial appealing.
Peacock: Dominant blue-green with occasional red, resembling a peacock's plumage. Named for the colour combination rather than the pattern geometry.
Pinfire: Small, dot-like colour patches distributed across the surface. Common; less commercially valuable than broad flash or rolling flash because the small scale of the colour patches reduces visual impact.
Factor 5: directionality
Directionality refers to the range of viewing angles from which the play-of-colour is visible. A stone that shows vivid play from any direction is more valuable than a stone that only shows colour from one specific angle and goes dark when tilted. Highly directional opals (technically described as "dead" at off-angles) are a significant commercial concern because they may appear excellent in a dealer's fixed display position but disappoint when worn as jewellery (GIA; Wise, 2016).
Doublets and triplets: what they are and how to identify them
Assembled opals are composites that present a natural opal layer on a dark backing (doublet) or with an additional clear quartz or glass dome on top (triplet). They are commercially legitimate as long as they are properly disclosed, but they must not be sold as solid opals at solid opal prices.
Doublet: A thin slice of natural precious opal cemented to a dark backing material (usually black ironstone, black plastic, or potch). The dark backing gives the thin opal layer a black-opal appearance at a fraction of solid black opal cost. Legitimate when disclosed.
Triplet: A thin slice of natural opal sandwiched between a dark backing and a clear dome of quartz or glass. The dome magnifies and protects the thin opal layer. Even more affordable than doublets. Legitimate when disclosed.
How to identify assembled stones: View the stone from the side while immersing or wetting its base. A solid opal has consistent material throughout. A doublet shows a clearly visible join line at the junction between the opal layer and the backing. A triplet shows two join lines (opal layer, backing) and the dome material has a different lustre from natural opal. Under magnification, the join line is usually obvious. Any side view of a fine black opal suspected to be a doublet should be standard practice before purchase (GIA; Wise, 2016).
Price reference for opal (2024–25)
| Type and quality | Size | Approx. USD per carat |
|---|---|---|
| Black opal (N1–N2), vivid red play, harlequin/rolling flash | 3–10ct | USD 5,000–50,000+ |
| Black opal (N1–N3), vivid play, broad flash | 2–8ct | USD 1,000–10,000 |
| Black opal (N2–N4), good play, blue-green dominant | Any | USD 200–2,000 |
| Boulder opal, good play, dark ironstone | Any | USD 100–1,500 |
| White opal, vivid play | Any | USD 50–500 |
| Commercial white opal | Any | USD 5–80 |
| Doublet or triplet (disclosed) | Any | USD 5–50 |
Approximate ranges 2024–25. Lightning Ridge black opal with fine red harlequin pattern above 5 carats has achieved USD 50,000–150,000+ per carat at specialist auction. Sources: GIA; Wise (2016); Christie's; dealer benchmarks. Not price guarantees.
Frequently asked questions
Should I buy an opal doublet or triplet for everyday wear?
For everyday wear jewellery at a modest budget, a disclosed doublet or triplet provides the opal appearance at accessible cost, but with specific limitations: the cemented join can deteriorate if the stone is immersed in water or cleaning solvents, potentially separating the layers. Ultrasonic and steam cleaning are not appropriate. For a ring worn daily, the physical vulnerability of doublets and triplets is a meaningful concern. A solid commercial white opal, while less spectacular in appearance, is more durable for daily wear than an assembled stone of equivalent price. For the finest jewellery and investment, only solid opals should be considered.
Does red fire in an opal mean it is a fire opal?
No. "Fire" in the description of an opal's play-of-colour refers to the vivid red, orange, and yellow spectral colours in the play-of-colour display. This is different from "fire opal," which is a specific variety name for the Mexican orange-red transparent opal that may or may not show play-of-colour. When a dealer says a Lightning Ridge black opal "has fire" or "shows fire," they mean it displays red and orange in its play-of-colour, this is a desirable quality description. When a dealer says "fire opal," they mean a separate variety from Mexico.
How should I store fine opal?
Store fine opal in a soft cloth pouch or a padded box, away from other harder gems that can scratch the surface. Avoid very low humidity environments for extended periods, some collectors store opals wrapped in a slightly damp cloth in a sealed container if the climate is extremely arid. Do not use ultrasonic cleaners, steam cleaners, or solvents. Clean with warm water and a soft cloth only. For long-term storage, keep opal away from heat sources and direct sunlight.
Sources cited in this article
- GIA Gem Reference Guide. (2006). Gemological Institute of America. (pp. 62–69)
- Wise, R.W. (2016). Secrets of the Gem Trade (2nd ed.). Brunswick House Press. (pp. 201–215)
- Australian Opal Centre. Opal grading standards and education. australianopalcentre.com.
- GIA Colored Stone identification. gia.edu.