Cup-and-Peg Setting

The standard mounting method for half-drilled pearls in fine jewellery

The cup-and-peg setting is the principal technique used to mount half-drilled pearls — most commonly in earring studs, solitaire pendants, and ring centres — in which a small metal component comprising a shallow concave cup and a short projecting peg is adhesively secured into the pearl's drilled cavity. The method is considered standard practice in quality pearl jewellery because it preserves nacre integrity, presents a clean aesthetic with no visible post or wire, and distributes mechanical stress across the pearl's base rather than concentrating it at a single drill point.

Construction and Components

The setting itself is a two-part unit cast or fabricated in the mounting metal — typically 18-carat yellow, white, or rose gold, platinum, or sterling silver. The cup is a shallow, slightly domed or flat-bottomed disc whose diameter is matched closely to the pearl's girdle, so that the pearl sits flush and centred without gaps. The peg — also called a pin or post — rises perpendicularly from the centre of the cup's upper face. Its diameter is engineered to fit snugly within the half-drilled cavity without forcing the nacre walls apart; standard peg diameters range from approximately 0.7 mm to 1.2 mm depending on pearl size and drill-hole gauge.

The cup's underside connects to the jewellery finding: an earring post, a bail loop, a ring shank, or a pendant connector. In high-end manufacture these are cast as a single unit; in commercial production the cup-and-peg component is often a separate finding soldered or fused to the base setting after the main piece is fabricated.

The Adhesive Bond

Securing the peg within the drill hole relies entirely on adhesive rather than mechanical clamping. Two-part epoxy resin is the most widely used bonding agent in the trade, valued for its high shear strength, gap-filling properties, and resistance to the mild acids present in perspiration. Jeweller's cyanoacrylate adhesives are sometimes employed for rapid assembly in commercial settings, though they are generally considered less durable than epoxy for long-term wear. Some specialist workshops use UV-curing adhesives that allow precise repositioning before the bond is set.

Correct adhesive application is critical. The peg and the interior of the drill hole are cleaned of oils and polishing compounds before bonding; a thin, even coat of adhesive is applied to the peg rather than flooding the cavity, which could cause hydraulic pressure to crack the nacre during insertion. The pearl is pressed firmly onto the peg and rotated slightly to distribute the adhesive, then held or jigged in position until the bond cures. Properly executed, the join is effectively invisible: the cup's rim meets the pearl's base in a continuous, unbroken line.

Why Half-Drilling Rather Than Full Drilling

The choice to half-drill a pearl rather than drill it through entirely is driven by both structural and aesthetic considerations. A full-drilled pearl — standard for strung necklaces and bracelets — has a channel running from one pole to the other, which weakens the nacre and, in smaller pearls, can compromise the roundness of the surface at the drill exits. For a stud earring or pendant solitaire, where only one point of attachment is needed, half-drilling removes far less material, leaving the pearl's opposite hemisphere entirely intact and preserving the full visual impact of its surface lustre and orient.

The cup-and-peg method also allows the jeweller to orient the pearl's finest face outward. Because the pearl is not threaded onto a fixed wire, the craftsperson can rotate it freely during assembly to present the most lustrous, blemish-free surface to the viewer before the adhesive sets — a degree of control unavailable when knotting or stringing through a full-drilled hole.

Cup Profile and Pearl Fit

The geometry of the cup is not incidental. A cup whose diameter is too small leaves a visible gap between the pearl's base and the metal, creating a shadow line that diminishes the setting's refinement. A cup that is too large crowds the pearl's girdle and can cause chipping of the nacre edge. In bespoke and high-end production, cups are selected or custom-fabricated to match the specific pearl being mounted, with the cup diameter typically set at approximately 40–50 per cent of the pearl's diameter for round and near-round specimens.

For baroque or drop-shaped pearls, the cup may be slightly domed or contoured to follow the pearl's base profile. Keshi pearls and other irregular forms sometimes require custom-shaped cups or a bed of bezel-style metalwork in place of a standard cup, though the peg-and-adhesive principle remains the same.

Durability and Maintenance Considerations

The principal vulnerability of a cup-and-peg setting is adhesive failure. Prolonged exposure to heat — from ultrasonic cleaners, steam cleaners, or even extended direct sunlight — can soften or embrittle the epoxy bond, eventually allowing the pearl to work loose. For this reason, pearl jewellery mounted by the cup-and-peg method should never be cleaned ultrasonically or with steam, and should be the last item applied when dressing (after perfume, hairspray, and cosmetics) and the first removed. These precautions are standard advice from pearl dealers, gemmological laboratories, and jewellery care guidelines.

When adhesive failure does occur, re-pegging is straightforward: the old adhesive is dissolved with acetone or a dedicated epoxy solvent, the peg and cavity are cleaned, and the pearl is re-bonded. Provided the nacre walls of the drill hole have not been damaged, a pearl can be re-set multiple times without structural compromise.

Use Across Pearl Types

The cup-and-peg setting is employed across the full range of pearl types used in fine jewellery. Akoya pearls, whose relatively modest size (typically 6–9 mm) and high lustre make them the dominant choice for classic stud earrings, are perhaps most commonly encountered in this setting. South Sea and Tahitian pearls, which command higher prices and are frequently set as single-stone pendants or earring drops, benefit particularly from the method's ability to showcase the pearl's surface without the distraction of a visible wire or post. Freshwater pearls, increasingly used in contemporary fine jewellery, are similarly mounted when used as solitaires.

In the Trade

Cup-and-peg findings are manufactured in standardised sizes and sold as components to jewellers worldwide. Major findings suppliers offer them in a range of cup diameters (commonly 4 mm through 12 mm), peg lengths, and metal types. In Japan — historically the centre of Akoya pearl cultivation and pearl jewellery manufacture — the cup-and-peg assembly is known colloquially as a pin setting, and its correct execution is considered a basic competency of pearl jewellery craftsmanship. Quality control in reputable pearl houses includes a pull-test of the adhesive bond before pieces leave the workshop.

When purchasing pearl stud earrings or pendants, the cup profile and metal quality are indicators of overall production standard. A well-fitted cup in solid gold or platinum, with a clean solder join to the earring post and a pearl that sits level and flush, signals careful manufacture. A loose pearl, a visible gap at the cup rim, or a pearl that can be rotated after setting are signs of poor adhesive application or mismatched component sizing.