A faceting jig — sometimes called a hand jig or, in historical lapidary literature, a jamb-peg jig — is a simple mechanical device used to hold a dopped stone at a controlled angle against a rotating lap, enabling the cutter to grind and polish flat facets without the precision mechanisms of a dedicated faceting machine. Jigs occupy the practical space between entirely freehand cutting and fully engineered faceting equipment, and they remain relevant for training purposes, field use, and budget-conscious lapidary work.

Construction and Mechanics

In its most common form, a faceting jig consists of three functional elements: a dop holder that grips the metal dop stick to which the rough stone is cemented; an adjustable arm or shaft that sets the height and therefore the angle at which the stone meets the lap surface; and some form of angle reference — typically a graduated protractor arc or a series of fixed notches — that allows the cutter to approximate a desired facet angle. The assembly may be entirely hand-held, with the cutter resting the jig against a peg or pin fixed to the lap surround (the defining feature of the classical jamb-peg arrangement), or it may be bench-mounted with a pivot point that constrains the arc of movement.

The jamb-peg variant, documented extensively in John Sinkankas's foundational lapidary texts, relies on a wooden or metal peg set into the splash pan or table at a fixed distance from the lap centre. The cutter hooks the dop stick or jig arm over this peg, using body pressure and hand position to control the cutting angle. Indexing — the rotation of the stone to present successive facets in their correct azimuthal positions — is managed by the cutter's judgement rather than by a mechanical index wheel, which is the principal source of imprecision compared with modern faceting machines.

Capabilities and Limitations

A faceting jig can produce recognisable faceted stones, including standard rounds, ovals, and simple step cuts, in the hands of a practised operator. For softer, lower-value materials — calcite, fluorite, or practice glass — the lack of mechanical repeatability is an acceptable trade-off against cost and portability. However, several limitations are inherent to the design:

• Angle repeatability is dependent on the cutter's consistency of hand pressure and positioning; small variations produce facets that do not meet cleanly at their junctions, resulting in visible ridges or uneven meets.
• Index accuracy is approximate; without a mechanical index wheel, achieving the precise azimuthal spacing required for a well-proportioned brilliant cut demands considerable experience.
• Cheater adjustment — the fine lateral shift used on precision machines to correct a slightly misaligned facet — is absent or rudimentary, making corrections difficult once a facet is partially cut.
• Polishing of hard materials (corundum, spinel, chrysoberyl) is particularly challenging, as the consistent pressure and angle control required for a high polish are difficult to sustain manually over many facets.

Historical and Educational Context

Before the widespread availability of affordable cam-arm and mast-type faceting machines in the latter half of the twentieth century, jig-based and jamb-peg cutting represented the accessible entry point into faceting for amateur lapidaries across Europe, North America, and parts of Asia. Traditional cutting centres in Sri Lanka and parts of South and South-East Asia have long employed variants of the jamb-peg principle, with skilled cutters producing commercially acceptable stones through accumulated tactile expertise rather than mechanical precision. Sinkankas's Gem Cutting: A Lapidary's Manual remains the most cited English-language reference for jig construction and technique.

In a contemporary educational setting, the faceting jig retains value as a teaching instrument precisely because it demands that the student develop an intuitive understanding of angle, pressure, and lap behaviour before relying on the mechanical assists of a full machine. Some lapidary programmes introduce jig work early in the curriculum for this reason.

Relationship to the Jamb Peg

The terms faceting jig and jamb-peg jig are sometimes used interchangeably, though strictly the jamb peg refers specifically to the fixed fulcrum peg arrangement rather than to all hand-held faceting aids. The jamb peg is the older and more geographically widespread form; the term faceting jig tends to appear in mid-to-late twentieth-century North American lapidary literature to describe bench-mounted or more engineered variants that retain manual angle-setting but add a degree of structural rigidity absent from the bare jamb-peg method.