The buff-top is a mixed cutting style in which the crown of a gemstone is shaped as a smooth, convex dome — identical in profile to a cabochon — while the pavilion is faceted in the manner of a step cut or brilliant cut. The result is a stone that presents two distinct optical personalities simultaneously: the silky, uninterrupted surface of a cabochon above the girdle, and the light-returning geometry of a faceted base beneath it. This combination makes the buff-top one of the most practically useful cuts in the lapidary's repertoire, particularly for materials that are too dark, too included, or too optically complex to perform well in either a purely faceted or a purely cabochon form.

Optical Rationale

The fundamental problem the buff-top solves is one of tonal balance. A deeply saturated corundum — a dark blue sapphire or a richly coloured ruby — cut as a full cabochon will often appear nearly opaque in the centre, a phenomenon sometimes called extinction or, informally, a "black window." The same rough cut as a standard faceted oval or cushion may, conversely, appear washed-out and pale, because the faceted crown disperses light before it has had time to interact fully with the body colour. The buff-top navigates between these extremes: the domed crown slows and diffuses incoming light, allowing it to saturate through the body of the stone, while the faceted pavilion reflects that light back toward the observer with directional brilliance. The net effect is a stone that appears richer in colour than a faceted equivalent and livelier than a plain cabochon.

The smooth crown also serves a secondary optical function for phenomenal stones. In star sapphires and star rubies, the asterism produced by intersecting needle-like inclusions of rutile — the silk — is displayed only across a curved, polished surface. A faceted crown would fracture the star into disconnected glints. The buff-top therefore preserves the star on the crown while the faceted pavilion adds the depth and luminosity that a flat-bottomed or uncut base cannot provide. Similarly, cat's-eye chrysoberyl and other chatoyant materials benefit from the same logic: the dome focuses the chatoyant band, while the pavilion contributes reflected light that prevents the stone from appearing dull or lifeless.

Construction and Proportions

In practice, the buff-top is most commonly executed with a step-cut pavilion — rows of elongated, parallel facets running parallel to the girdle — though brilliant-cut pavilions are not unknown, particularly in smaller stones where the step arrangement would produce facets too narrow to be optically effective. The girdle itself is typically left as a narrow, polished band, and the transition between the curved crown and the upper row of pavilion facets is usually clean and abrupt rather than graduated.

The height of the dome is a critical variable. A low, flat dome reduces the cabochon effect and allows more light to enter at oblique angles, brightening the stone but weakening any optical phenomenon. A high, steeply curved dome intensifies asterism or chatoyancy and deepens apparent colour but can make the stone appear glassy or "soapy" if the material is very transparent. Skilled cutters calibrate dome height to the specific optical character of each piece of rough, and this judgement — essentially invisible in the finished stone — is a significant part of the craft value of a well-executed buff-top.

Outline shapes most commonly used are oval and round, both of which suit the symmetrical curvature of the dome, though cushion and pear buff-tops are produced for certain markets. The oval is by far the most prevalent, as it allows the cutter to orient the stone's optical axis correctly — vertical in a star stone, perpendicular to the fibre direction in a cat's-eye — while retaining maximum weight from the original rough crystal.

Historical Context

The buff-top gained widespread recognition in the early twentieth century, a period during which the trade in phenomenal corundum from Burma (present-day Myanmar) was expanding rapidly and cutters were seeking ways to maximise the commercial appeal of star stones without sacrificing the brilliance that buyers accustomed to faceted gems had come to expect. The style was not an invention of that era — hybrid cuts combining polished and faceted elements have existed since at least the Renaissance — but the early 1900s saw the buff-top codified as a distinct, named cutting style with recognised commercial applications.

The term "buff-top" itself derives from the buffing or polishing action applied to the crown surface, distinguishing it from the grinding and faceting operations applied to the pavilion. "Buffy top" appears occasionally in older trade literature as a variant spelling, though "buff-top" and "buff top" are the forms most consistently used in contemporary gemmological writing.

Applications in the Trade

The buff-top is most closely associated with the following categories of material:

• Star sapphires and star rubies: The classic application. Fine six-rayed stars from Sri Lanka, Burma, and Thailand are routinely cut as buff-tops to display asterism while maximising the apparent depth and colour of the stone.
• Cat's-eye chrysoberyl and other chatoyant stones: The curved crown focuses the chatoyant band; the faceted pavilion provides the reflective backdrop that makes the eye appear to float above a luminous interior.
• Translucent to semi-transparent corundum: Sapphires and rubies of moderate transparency that are too included for a high-quality faceted stone but too fine in colour to be reduced to a plain cabochon are frequently buff-topped as a practical compromise.
• Colour-zoned rough: When colour is concentrated near the base of a crystal, a faceted pavilion can be oriented to reflect that zone back through the dome, producing a more evenly saturated appearance than a cabochon would achieve.
• Spinel and tourmaline: Deeply saturated specimens of these species are occasionally buff-topped for the same tonal-balance reasons that apply to corundum.

In the auction and retail market, buff-top stones occupy a distinct position. They are not regarded as equivalent to fully faceted stones of comparable weight and colour — the absence of a faceted crown is generally reflected in price — but a well-cut buff-top displaying a sharp, centred star or a crisp chatoyant eye commands significant premiums over a plain cabochon of the same material. Gemmological laboratory reports from institutions such as the GIA and Gübelin routinely note the cutting style as "buff-top" or "cabochon crown, step-cut pavilion" in their descriptions, and this notation is considered material information for auction purposes.

Gemmological Identification

Identifying a buff-top in hand is straightforward: examination of the profile reveals the characteristic dome above the girdle and the stepped or faceted geometry below. Under magnification, the crown surface shows the smooth, uninterrupted polish of a cabochon, while the pavilion facets display the flat, reflective planes of conventional lapidary work. This distinction is relevant when assessing treatments: fracture-filling or surface coating on the crown of a buff-top may be more difficult to detect than on a faceted stone, because the curved surface scatters reflected light in a way that can mask surface irregularities. Careful examination under fibre-optic illumination at oblique angles is recommended when treatment disclosure is in question.

Further Reading

• GIA Gems & Gemology — Corundum and Asterism
• GIA Gem Encyclopedia — Sapphire
• International Gem Society — Cabochon vs. Faceted Gems