A dop transfer jig is a mechanical fixture used in faceting to transfer a partially cut gemstone from one dop stick to another whilst maintaining exact, repeatable alignment of the stone's optical and geometric axis. Without such a device, the critical angular relationship between the crown facets already cut and the pavilion facets yet to be cut would be lost, resulting in misaligned girdle planes, asymmetrical meets, and wasted material. The transfer jig is therefore regarded as an essential precision instrument in any serious faceting workshop.

Purpose and Principle

Faceting a gemstone proceeds in two broad stages: the pavilion (lower half) is cut and polished first, then the stone is re-dopped — inverted and mounted on a new dop — so that the crown (upper half) can be worked. The challenge is that the new dop must grip the stone in precisely the same rotational and axial orientation as the original, or the crown facets will not align with the pavilion facets at the girdle. Even a deviation of one or two degrees produces visible asymmetry in the finished stone.

The transfer jig solves this by holding both the original dop and the receiving dop in a rigid, fixed-geometry cradle simultaneously. The two dop sticks are seated in opposing collets or V-blocks that share a common centreline. With both dops locked in place, fresh dopping wax or a two-part epoxy adhesive is applied to the receiving dop, which is then brought into contact with the stone while the assembly is held immobile. Once the adhesive cures, the original dop is released, and the stone is now mounted on the new dop in a geometrically defined orientation.

Construction and Variants

Transfer jigs are manufactured in several configurations, though all share the same functional principle. The most common form consists of a machined aluminium or brass body with two collet sockets bored on the same axis, facing one another. The sockets accept standard dop stick diameters — typically 3 mm, 4 mm, 6 mm, and occasionally metric equivalents — and are secured by set screws or spring-loaded clamps. Higher-end jigs incorporate a fine-thread adjustment on one socket to allow micro-correction of the axial gap, accommodating stones of varying depth.

A second variant, sometimes called a transfer block, uses a flat machined plate with two parallel channels rather than opposed collets. This design is particularly suited to transfer between dops of different diameters, as each channel can be sized independently. Some advanced jigs include a rotational index — a detented ring calibrated in degrees — allowing the cutter to introduce a deliberate, measured rotation between the two dops when the design calls for offset crown and pavilion facet rows, as in certain Portuguese or fantasy cuts.

Use with Dopping Wax and Epoxy

Traditional dopping wax, a shellac-based thermoplastic compound, requires the transfer jig to be used in conjunction with a heat source. The receiving dop is warmed, wax is applied, and the jig holds everything in alignment while the wax is pressed against the stone and then cooled. Because wax shrinks slightly on cooling, the jig must remain clamped until the wax is fully set; premature release can introduce the very runout the jig is designed to prevent.

Two-part epoxy adhesives — notably cyanoacrylate formulations and slower-curing structural epoxies — have become increasingly popular for transfer work because they do not require heat and exhibit minimal shrinkage. The jig's role is unchanged: it holds the geometry fixed during the cure period, which may range from a few minutes to several hours depending on the adhesive selected. Epoxy transfers are particularly favoured for heat-sensitive stones such as tanzanite, opal, and certain treated corundum where elevated temperatures risk damage or colour change.

Alignment Accuracy and Runout

The quality of a transfer jig is measured primarily by its runout — the degree to which the transferred stone deviates from true axial alignment when mounted in the faceting machine's quill. A well-machined jig held to close tolerances can achieve runout of less than 0.05 mm, which is imperceptible in the finished stone. Cheaper jigs with worn collets or poorly bored sockets may introduce runout of 0.2 mm or more, which manifests as a girdle that is not level and facets that do not meet cleanly at the culet or table.

Cutters working in competition faceting — where judging criteria include symmetry, meet-point precision, and girdle levelness — typically invest in jigs machined to tighter tolerances and inspect the transferred stone under magnification before proceeding to crown work.

In the Trade and Workshop

Dop transfer jigs are produced by a number of lapidary equipment manufacturers and are available as standalone accessories compatible with most faceting machine dop systems. They are not interchangeable across all machine brands without attention to dop diameter standards, and cutters should confirm compatibility before purchase. The jig is a relatively modest investment compared to the faceting machine itself, yet its contribution to finished stone quality is disproportionately significant — a point consistently emphasised in faceting instruction programmes at guild and society level.