Open-Back Setting — Light From Below the Stone
Open-Back Setting — Light From Below the Stone
A setting in which the pavilion of the gemstone is exposed through a pierced or open metal backing, the standard practice since the 18th century
An open-back setting is a setting in which the pavilion of the gemstone is exposed through a pierced or fully open metal backing, allowing ambient light to enter the stone from below. The design became standard in fine jewellery from the late eighteenth century onward as gem-cutting improved and the optical importance of light transmission through the pavilion of a faceted stone became understood. The contrast is with closed-back settings, common in earlier periods, in which the pavilion sat against a foiled metal backing and the stone's apparent colour and brightness were enhanced by the foil rather than by transmitted light. Open-back settings are now the default for virtually all transparent faceted stones in modern fine jewellery, with the principal exceptions being antique-style work and specific design choices for which a closed back is preferred.
Why open-back replaced closed-back
Pre-eighteenth-century cutting techniques produced stones — table cut, rose cut, and earlier brilliant variants — that did not depend on transmitted light from the pavilion for their appearance. The cutting was shallower, the proportions less optimised for total internal reflection, and the stones often displayed surface character rather than internal brilliance. Closed-back settings with foil backing made sense in this context: the foil reflected light back through the stone and could be coloured to enhance or correct the apparent body colour.
The development of the brilliant cut through the eighteenth and nineteenth centuries — culminating in Marcel Tolkowsky's mathematical analysis of ideal proportions in 1919 — demonstrated that the brilliance and fire of a well-cut diamond depend on light entering through the table and crown, refracting within the pavilion, and returning to the eye through the table. Allowing additional light to enter from below the pavilion enhances the overall light return; closing the pavilion against a foil back at best contributes nothing and at worst introduces colour or absorbs light.
The same logic applies, with adjustments for the species' specific optical properties, to coloured stones. Sapphires, rubies, emeralds, tourmalines, and most other transparent coloured stones look better with light entering from the pavilion than against a foil back. By the late nineteenth century, the open-back setting had become the standard for fine work, with closed-back settings retained for specific traditional applications.
Design and construction
The simplest open-back setting is a bezel with the back fully removed, leaving the pavilion exposed through a circular or shaped opening. More elaborate open-back constructions use pierced gallery work, where decorative metal patterns frame the open back without fully blocking light. The choice between fully open and partially pierced depends on design considerations, the strength required of the setting, and the aesthetic relationship between the back of the piece and the front.
Open-back settings also permit cleaning of the pavilion, inspection of the stone for damage, and removal and resetting more easily than closed-back constructions. For ring settings particularly, the ability to clean accumulated dirt from the pavilion is a practical benefit that closed-back settings sacrifice.
When closed-back is appropriate
Closed-back settings remain appropriate for several specific applications. Antique-style restoration work requires closed backs to match the period idiom, and some restored eighteenth-century pieces are deliberately reset with closed backs and modern metallic-foil substitutes for authenticity. Foil-backed Georgian paste, garnet, and topaz jewellery represents a category in its own right, and any modern restoration of such pieces should preserve the closed-back foil construction.
Some opaque or translucent stones are appropriately set in closed-back constructions: turquoise, lapis lazuli, malachite, and similar materials do not benefit from transmitted light and may be served better by a closed back that supports the cabochon and presents a clean line at the back of the piece. Cabochon-cut transparent stones — moonstone, star sapphire, star ruby — are sometimes closed-back set for similar reasons.
In the trade
Open-back is the default specification for any modern fine jewellery setting transparent faceted stones. Customers presented with a closed-back setting on a transparent stone in modern work should ask why; in most cases the answer is either antique restoration, deliberate aesthetic choice, or a low-end manufacturing economy. For working jewellers, the standard goldsmithing manuals — Oppi Untracht, Tim McCreight, and the broader bench-jewellery literature — treat open-back as the default for transparent faceted-stone settings. See also closed-back setting, bezel setting, and foil-backed jewellery for related entries.