A double cabochon is a gemstone cut in which both the crown (upper surface) and the pavilion (lower surface) are convex, producing a symmetrical or near-symmetrical lens profile. Unlike the standard, or single, cabochon — which presents a domed crown above a flat or only gently curved base — the double cabochon curves outward on both faces, giving the finished stone a shape broadly analogous to a biconvex optical lens. The style is employed principally for translucent and semi-transparent materials in which light passing through the stone, as well as light reflected from within it, contributes to the gem's visual character. It is particularly associated with phenomenal stones: those displaying asterism, chatoyancy, adularescence, or similar optical effects.

Geometry and Proportions

In a conventional single cabochon the pavilion is kept flat or only slightly rounded so that the stone sits securely in a bezel setting and presents a stable base to the setter. The double cabochon abandons that flat base in favour of a second dome, which may be shallower than the crown dome (an asymmetric double cabochon) or of approximately equal curvature (a symmetric, or true, double cabochon). The resulting cross-section is elliptical or lenticular. Girdle outline — the plan-view shape — remains as variable as in any cabochon: oval is by far the most common, but round, cushion, and occasionally pear or marquise outlines are encountered.

Because the pavilion dome adds depth to the stone, double cabochons are generally taller, relative to their width, than single cabochons cut from the same rough. Cutters must therefore select rough of sufficient thickness, and the finished stone will sit higher above the setting plane. Bezel settings are almost universal; prong settings are rarely practical because the curved pavilion offers no flat ledge against which prongs can bear.

Optical Rationale

The primary argument for the double cabochon form is photonic: a convex pavilion refracts and redirects light entering through the crown in a manner that a flat pavilion cannot. In translucent stones, light that penetrates the gem is scattered by internal inclusions, silk, or structural features; the curved pavilion acts as a diverging surface on exit, spreading that scattered light back upward through the crown and intensifying the luminous, three-dimensional quality that makes phenomenal gems desirable.

For stones exhibiting chatoyancy — the cat's-eye effect produced by parallel fibrous inclusions or hollow tubes oriented perpendicular to the stone's length — the double cabochon's additional depth ensures that the band of reflected light (the eye) is sharp and well-centred. A pavilion that is too flat can cause the eye to appear weak or to migrate toward the girdle. The convex pavilion helps concentrate reflected light toward the apex of the crown, where the eye is most vivid.

In stones displaying asterism — the star effect produced by two or more intersecting sets of oriented inclusions — the double cabochon similarly helps focus the star's rays. The dome height on both faces must be calibrated carefully: too steep a crown and the star's legs become short and stubby; too shallow a pavilion and the reflected silk is insufficiently gathered. Experienced lapidaries working with star sapphire or star ruby will adjust the pavilion curvature empirically, testing the stone under a point light source at each stage of grinding.

Adularescence in moonstone — the billowing, floating glow caused by light scattering between alternating layers of orthoclase and albite feldspar — is also enhanced by the double cabochon. The curved pavilion allows light to enter the stone from a wider range of angles, feeding the internal scattering layers more effectively than a flat base would. Fine moonstone from Meetiyagoda, Sri Lanka, and from the classical deposits of Adularmont in Switzerland, is frequently cut in this form to maximise the blue adularescent sheen.

Materials Commonly Cut as Double Cabochons

• Chrysoberyl cat's-eye — the benchmark phenomenal gem; the double cabochon is considered the standard cut for fine specimens from Thattekkad (Kerala, India) and Hematita (Minas Gerais, Brazil).
• Star sapphire and star ruby — corundum with oriented rutile silk; classic material from Mogok (Myanmar), Ratnapura (Sri Lanka), and Chanthaburi (Thailand).
• Moonstone — feldspar group; Sri Lankan and Indian material is routinely cut in this form when adularescence is strong.
• Star rose quartz — the diffuse asterism of this material benefits from the added depth a double pavilion provides.
• Alexandrite cat's-eye — rare chrysoberyl combining colour-change with chatoyancy; double cabochon cutting is standard.
• Aquamarine and tourmaline cat's-eyes — less common, but the same optical principles apply.

Cutting Considerations

Fashioning a double cabochon demands greater skill than producing a single cabochon, chiefly because the lapidary must maintain symmetry across two curved surfaces simultaneously while preserving the orientation of the optical phenomenon. For chatoyant stones, the fibrous inclusions must run precisely parallel to the girdle plane; any tilt displaces the eye from centre. For asterism, the crystallographic axis producing the star must be perpendicular to the table — or rather, to the apex of the crown dome — and this orientation must be established before grinding begins and maintained throughout.

The sequence of work typically proceeds as follows: the rough is first oriented under a point light source to locate the phenomenon's optimal position; a pre-form is sawn or ground to approximate the desired girdle outline; the crown dome is ground and polished first; the stone is then dopped (mounted on a dop stick) from the crown side, and the pavilion dome is ground and polished. Because the finished pavilion is convex, standard flat-lap dop techniques must be adapted — many cutters use a ball-and-socket dop or a curved grinding surface for the final pavilion work.

Weight retention from rough to finished stone is generally lower for double cabochons than for single cabochons of equivalent girdle dimensions, because material is removed from the pavilion that would otherwise remain as the flat base. This consideration is commercially significant for expensive rough such as fine alexandrite or high-quality star ruby.

Setting and Jewellery Use

The convex pavilion of a double cabochon creates a distinctive raised profile in a finished jewel. Bezel settings — whether plain, milgrain-edged, or split — are the conventional solution, as the metal wall of the bezel can be burnished against the curved girdle regardless of pavilion shape. Some contemporary designers exploit the lens-like form deliberately, setting double cabochons in open-back bezels or even suspending them in tension settings so that light can enter from below as well as above, fully realising the optical potential of the cut.

Historically, the double cabochon was well understood by Indian and Sinhalese lapidaries long before it was systematically described in Western gemmological literature. Many antique Mughal and Sri Lankan jewels feature moonstones and cat's-eye chrysoberyls cut in this form, their curved pavilions visible where settings have worn thin or been opened for examination.

Trade Nomenclature

In the trade the term double cab is the standard abbreviation. Some dealers and auction catalogues use the phrase lenticular cabochon when the two domes are of nearly equal curvature, though this usage is not universal. The GIA's gem identification and grading literature distinguishes the double cabochon from the single cabochon and from the hollow cabochon (in which the pavilion is concave rather than flat or convex), though the hollow cabochon is a rarity encountered mainly in lightweight assembled stones and certain antique hardstone carvings.

Further Reading

• GIA Gems & Gemology — Moonstone and the Feldspar Group
• GIA Gems & Gemology — Star Corundum
• International Gem Society — Cabochon Gem Cutting