Dop
Dop
The foundational holding device of the gem-cutter's art
A dop — also called a dop stick — is the small cylindrical or conical holder used to secure a rough or partially cut gemstone during faceting and polishing. Without a reliable means of holding the stone at a precisely repeatable angle, the geometry of a faceted gem could not be controlled; the dop is therefore as fundamental to the lapidary's practice as the grinding lap itself. Dops are manufactured in brass, aluminium, and occasionally hardwood, and are dimensioned to fit the quill or hand-piece of a faceting machine. They are available in a range of head diameters — typically from about 3 mm to 25 mm or more — so that stones of different girdle sizes can each be held with appropriate support.
Construction and Types
The working end of a dop, the part that contacts the stone, is shaped to suit the geometry of the cut being executed. The most common forms are:
- Flat dops — a plain, flat face used to hold the table of a stone while the pavilion facets are cut. The flat surface distributes adhesive evenly and is the standard choice for the first stage of cutting.
- Cone dops (also called V-dops) — a conical recess machined into the head, designed to cradle the pavilion of a partially cut stone when the cutter transfers to work the crown. The cone centres the stone automatically and provides mechanical support in addition to adhesive bonding.
- Wax dops — older or hand-made dops in which a collar of shellac-based wax forms the entire contact surface, shaped by the cutter to conform to the stone's geometry. These remain in use among traditionalists and for irregular or fragile material.
- Combination or step dops — machined with a stepped profile to accommodate stones with a pronounced girdle, common in step and emerald cuts.
Precision-machined dops intended for transfer operations are sometimes sold as matched pairs, with tolerances held tightly enough that the rotational and axial position of the stone is reproduced within a fraction of a degree when moved from one dop to its partner.
Adhesives: Wax and Epoxy
Two adhesive systems dominate modern lapidary practice. Dopping wax — a shellac-based thermoplastic compound, traditionally coloured dark brown or black — has been used for centuries. It is softened over a spirit lamp or small alcohol flame, pressed around the stone, and allowed to cool. Its principal advantage is reversibility: gentle reheating releases the stone without chemical solvents. Its limitation is sensitivity to heat generated during grinding; aggressive cutting on a dry lap can soften the wax and allow the stone to shift, ruining the geometry of a facet meet.
Epoxy adhesive, typically a two-part system with a working time of five to thirty minutes, offers a stronger and more heat-resistant bond. It is the preferred choice for stones that require prolonged polishing on harder laps, and for cutters working in warm climates where ambient temperature alone can compromise wax bonds. Release is achieved with acetone or other appropriate solvents, or by brief immersion in a freezer, which causes differential thermal contraction and breaks the bond cleanly. Some cutters apply a thin release layer — petroleum jelly or a proprietary parting agent — to the dop face before epoxying, making subsequent removal easier without compromising bond strength during cutting.
The Transfer Operation
Because a faceted stone has both a crown (upper half) and a pavilion (lower half), it must be held from two different directions at different stages of cutting. The transfer is the operation by which the stone is moved from the first dop — which held it during pavilion cutting — to a second dop that will hold the pavilion while the crown is cut. Accurate transfer is critical: any shift in the stone's orientation between the two dops will cause the crown and pavilion facets to be misaligned, producing a stone with poor light return and visible asymmetry.
A transfer block (or transfer jig) is the device used to accomplish this. It holds both dops in precise axial alignment while the adhesive on the new dop cures. The stone, still bonded to the first dop, is seated into the cone or flat of the second dop, which has been charged with fresh wax or epoxy. Once the new bond has set, the original dop is released — by heat if wax was used, or by solvent if epoxy — and cutting continues from the new orientation. Experienced cutters regard a clean, accurate transfer as one of the more demanding skills in the craft, particularly for small stones where the tolerances are unforgiving.
Dops in the Faceting Machine
The dop is inserted into the quill of a faceting machine — a precision-bored collet that holds the dop at a fixed height above the lap surface and allows it to rotate to indexed angular positions. The quill is mounted on an arm whose elevation angle (the cheater or angle adjustment) can be set to fractions of a degree, controlling the angle at which each facet meets the lap. The combination of angle setting, index gear position, and dop diameter determines the exact geometry of every facet cut. Because the dop must be removed and reinserted repeatedly — to change index positions, to inspect the stone, or to perform a transfer — the fit between dop and quill must be snug but not binding, and the dop's shank must be machined to a consistent diameter. Most modern faceting machines use a standardised shank diameter, commonly 6.35 mm (one quarter inch) or 8 mm, though this varies by manufacturer and national market.
Historical Context
The word dop derives from the Dutch dop, meaning a shell or cup — a reference to the small cup-shaped wax holders used by early Flemish and Dutch gem-cutters in Antwerp and Amsterdam from at least the sixteenth century. The great cutting centres of the Low Countries established the vocabulary of the lapidary's workshop, and many of those terms — dop, bruting, kerf — passed into English as the trade spread. Early dops were entirely of wood or bone, with the wax forming the entire functional head; the machined metal dop with its precisely formed cone or flat is a product of the industrial era, refined through the twentieth century alongside the development of purpose-built faceting machines.
Practical Considerations in the Trade
For professional cutters working with valuable rough, dop choice and adhesive selection are not trivial decisions. Stones with perfect cleavage — topaz, kunzite, fluorite — are vulnerable to cleavage fracture if thermal shock is applied during wax release; epoxy and solvent release are strongly preferred for such material. Heat-sensitive stones — ammolite, some treated opals, certain dyed or resin-impregnated material — may be damaged by the temperatures needed to soften dopping wax, again favouring cold-cure epoxy. Conversely, stones that must be oriented precisely to a crystallographic axis — star sapphires cut to centre the asterism, or alexandrite oriented to display the strongest colour change — require the cutter to position the stone carefully in the wax before it sets, a process more easily accomplished with the slower-cooling wax than with fast-setting epoxy.
The quality of a cutter's dops — their concentricity, the accuracy of their cone angles, the smoothness of their shanks — has a measurable effect on the precision of the finished stone. Among serious amateur and professional facetors, well-made dops from specialist suppliers are regarded as a worthwhile investment, and worn or damaged dops are replaced rather than tolerated.