A bearing — also termed a seat — is the engraved ledge or recess cut into the interior wall of a gemstone setting to receive and support the pavilion of a stone. It is one of the most consequential preparatory steps in the stone-setter's craft: a correctly cut bearing holds the gem at the intended depth and angle, prevents rocking or lateral shift, and distributes the mechanical pressure of setting evenly around the girdle. An imprecise bearing, by contrast, can crack a brittle pavilion, tilt the table out of plane, or cause a prong or bezel to seat unevenly, compromising both the security and the appearance of the finished mount.

Function and Geometry

The bearing must correspond closely to two measurements: the girdle diameter (or, in fancy-cut stones, the girdle outline) and the pavilion angle. When a round brilliant is to be set, the setter cuts a circular groove at the precise depth at which the girdle will sit flush with or just below the top of the setting wall. The groove's inner face is angled to match the pavilion's cone, so that contact is made along a continuous ring rather than at isolated points. This ring of contact is what prevents the stone from rocking under pressure and from shifting when the mount is worn.

For fancy shapes — ovals, pears, marquises, cushions — the bearing must follow the corresponding outline, which demands freehand work with a graver rather than the rotary burs that suffice for round stones. Asymmetric cuts such as the pear require particular care at the curved end and at the two wing points, where the girdle thickness often varies and the risk of chipping is highest.

Cutting Techniques

Bearings are cut with two principal tools: hart burs (also called bearing burs), which are cone-shaped rotary cutting heads used in a flex-shaft or pendant drill, and gravers — hand-held steel chisels of various profiles. Hart burs are efficient for round and near-round outlines; gravers give the setter fine control for corners, points, and corrections. The setter tests the fit repeatedly, lowering the stone into the setting and examining the girdle level and table plane before removing material further. The axiom in the trade is that metal removed cannot be replaced: cutting proceeds incrementally.

In channel settings, the bearing takes the form of a continuous groove running along two parallel walls, and every stone in the row must seat at precisely the same depth to keep the table surfaces level. In bezel settings, the bearing is cut around the full circumference of the bezel wall. In prong (claw) settings, a small notch is cut into the inner face of each prong; these individual notches collectively form the bearing, and their alignment is critical — if one notch is cut deeper than the others, the stone will tilt toward that prong when pressure is applied during setting.

Relation to Stone Hardness and Fragility

The bearing is of heightened importance when setting stones of low toughness or pronounced cleavage. Diamonds, despite their extreme hardness, cleave readily along octahedral planes; a bearing that concentrates pressure at a cleavage-parallel point on the girdle can initiate a fracture. Emeralds, which are typically heavily included and possess moderate toughness, demand a bearing that spreads load as broadly as possible. Tanzanite, with its pronounced cleavage in three directions, and opals, which are sensitive to both mechanical shock and thermal stress, require bearings that are particularly smooth and continuous. In each case, the setter may also line the bearing with a thin layer of jeweller's shellac or a modern adhesive to cushion the stone further, though this is supplementary to, not a substitute for, accurate mechanical fit.

In the Trade

Experienced setters assess a bearing by feel as much as by sight, lowering the stone and feeling for the slight resistance that indicates correct contact. A stone that drops too freely suggests the bearing is too deep or too wide; one that sits high and rocks indicates insufficient material has been removed. The quality of bearing preparation is one of the clearest markers distinguishing bench-trained setters from those with limited experience, and in high-end ateliers the preparation of bearings for important stones — particularly large coloured gems or old-cut diamonds with non-standard pavilion angles — may be entrusted only to senior craftspeople.