The cushion modified brilliant (CMB) is a cushion-shaped gemstone cut distinguished from the standard cushion brilliant by the addition of extra rows of pavilion facets beyond the conventional four mains per quadrant. Where a cushion brilliant produces broad, distinct flashes of light reminiscent of the old mine cuts from which it descends, the cushion modified brilliant subdivides those reflections into a denser, more fragmented pattern — commonly described in the trade as a crushed ice or broken glass effect. The style is now among the most prevalent cutting approaches for both diamonds and coloured stones, particularly sapphires, in the contemporary market.

Definition and GIA Classification

The Gemological Institute of America formally distinguishes the cushion modified brilliant from the cushion brilliant on its grading reports, and the distinction rests specifically on pavilion facet architecture. A standard cushion brilliant typically carries four pavilion main facets per quadrant, arranged in a pattern that echoes the round brilliant's pavilion geometry within a rounded-square or rectangular outline. The cushion modified brilliant introduces additional facet rows — most commonly producing six or eight pavilion mains per side — that break the larger reflective surfaces into smaller, more numerous mirrors. This structural difference is sufficiently significant that GIA treats the two as separate cut categories, each receiving its own designation on a diamond grading report.

The outline itself — a square or rectangular shape with softly rounded corners and gently curved sides — remains consistent between the two categories. The differentiation is therefore invisible from the face-up profile and can only be confirmed by examining the pavilion directly or by reference to a laboratory report.

Optical Character: Crushed Ice vs. Chunky Flash

The practical consequence of the additional pavilion facets is a fundamental shift in how the stone handles light. In a cushion brilliant, each pavilion main is large enough to return a coherent, identifiable flash of white or spectral light. The eye resolves individual reflections, and the stone displays what cutters and dealers call a chunky or bold pattern — broad, well-defined scintillation units that move dramatically as the stone or the light source shifts.

In the cushion modified brilliant, the subdivided pavilion facets each subtend a smaller solid angle to the observer's eye. The result is that no single reflection dominates; instead, the stone presents a continuous shimmer of smaller, rapidly alternating bright and dark zones. This is the crushed ice appearance — a term that has passed from trade slang into near-universal usage. The effect is particularly pronounced in stones with higher refractive indices, such as sapphire and spinel, where the greater bending of light amplifies the contrast between adjacent micro-reflections.

Neither pattern is objectively superior; preference is largely aesthetic and contextual. The crushed ice character of the CMB tends to mask inclusions effectively, since the fragmented light pattern draws the eye away from internal features. It can also make a stone appear slightly larger face-up relative to its carat weight, because the even distribution of brightness across the table gives an impression of greater spread. Conversely, the bold flash of a cushion brilliant may be preferred when the stone's colour saturation is the primary selling point, as larger reflective surfaces return more saturated colour to the eye in a single glance.

Facet Geometry and Cutting Considerations

The additional pavilion rows of a cushion modified brilliant are typically achieved by introducing an extra tier of break facets or by splitting the pavilion mains themselves, depending on the cutter's chosen approach. The crown geometry may mirror that of a standard cushion brilliant — star facets, upper girdle facets, and a table — or may itself be modified with additional upper girdle rows to complement the pavilion's increased complexity. When both crown and pavilion carry extra facet tiers, the result is sometimes described informally as a super ideal or high-performance cushion modified brilliant, though these designations are trade terms rather than laboratory classifications.

Proportions vary considerably across the CMB category. Table percentages typically range from approximately 55 to 70 per cent of the girdle diameter, with total depth commonly falling between 60 and 70 per cent. Because GIA does not assign a cut grade to cushion cuts (as it does to round brilliants), there is no standardised ideal range, and cutters exercise considerable latitude. The absence of a formal cut-grade system means that two stones both graded as cushion modified brilliants on a GIA report may differ substantially in their optical performance.

Prevalence in Diamonds and Coloured Stones

In the diamond trade, the cushion modified brilliant became the dominant cushion-cut style during the early decades of the twenty-first century, driven partly by consumer preference for the crushed ice aesthetic and partly by the efficiency with which the style can be cut from certain rough crystal shapes. Many mass-market cushion diamonds sold today are CMBs, and the designation appears routinely on GIA Diamond Grading Reports.

Among coloured stones, the cushion modified brilliant is particularly common in sapphires from Sri Lanka, Madagascar, and Australia, where the cutting is frequently performed in Bangkok or other Thai cutting centres. The style suits sapphire well: the stone's refractive index of approximately 1.762–1.770 generates strong internal reflections, and the fragmented pavilion pattern distributes colour evenly across the face-up view, reducing the risk of colour zoning or windowing that can afflict poorly cut cushions. Heat-treated sapphires destined for the commercial and fine commercial market are very frequently cut as CMBs for precisely these reasons.

Ruby, spinel, and alexandrite are also encountered in cushion modified brilliant cuts, though the style is less universal in those species. For alexandrite in particular, some cutters prefer the larger pavilion facets of a cushion brilliant, arguing that the broader reflective surfaces better display the colour-change phenomenon by returning more saturated colour in each flash.

Laboratory Identification and Grading Reports

GIA grading reports for diamonds specify the cut style as either Cushion Brilliant or Cushion Modified Brilliant in the shape and cutting style field. This distinction is determined by the laboratory's gemologists examining the pavilion facet arrangement, either directly under magnification or through digital imaging. The CMB designation does not carry an associated cut-quality grade on GIA reports, unlike the round brilliant, which receives Excellent through Poor grades.

Other major laboratories — including the American Gem Society Laboratories (AGSL), the International Gemological Institute (IGI), and Gübelin — may use slightly different terminology or classification criteria, and it is not uncommon for a stone graded as a cushion modified brilliant by one laboratory to be described simply as a cushion brilliant by another. Buyers relying on laboratory reports for precise cut-style identification should confirm the issuing laboratory's classification methodology.

For coloured stones, most laboratories do not distinguish between cushion brilliant and cushion modified brilliant on their reports, recording the shape simply as cushion or cushion mixed cut. The CMB designation is therefore primarily a diamond-trade and diamond-laboratory concept, though gemmologists working with coloured stones increasingly apply the same vocabulary informally.

In the Trade

The cushion modified brilliant occupies a curious position in the market: it is simultaneously the most commercially prevalent cushion cut and, among certain connoisseur buyers, the less favoured of the two cushion categories. Collectors who prize the antique character of the cushion outline — its historical association with the old mine cuts of the eighteenth and nineteenth centuries — often prefer the bold, chunky flash of a cushion brilliant, which more closely approximates the optical behaviour of those earlier stones. The crushed ice pattern of the CMB, by contrast, is perceived by some as a modern, somewhat anonymous aesthetic that sacrifices individuality for even brightness.

That said, the CMB's practical advantages — effective inclusion masking, strong face-up spread, and broad availability across a wide price range — ensure its continued dominance in the commercial market. For buyers seeking a cushion-cut diamond or sapphire at a given budget, the cushion modified brilliant will almost invariably represent the majority of available options.

Further Reading

• GIA — The 4Cs: Cut
• Gems & Gemology — Cushion-Cut Diamonds
• GIA Gem Encyclopedia