FACETCAM REFERENCE — GLOSSARY

The language of faceting.

45 terms, each with a plain definition and the detail behind it — the same glossary FacetCAM ships inside the workspace.

Barion

A cutting style combining a brilliant-style crown with a step-cut pavilion, or vice versa.Invented by Basil Watermeyer in 1971. Barion cuts often maximize brilliance while retaining weight from the rough stone.

Brilliance

White light returned to the viewer from within a gemstone.Brilliance depends on the refractive index of the material and the angles at which light enters and exits the stone. Higher RI materials can achieve greater brilliance.

Brilliant cut

A faceting style using triangular and kite-shaped facets radiating from the center, designed to maximize light return.The standard round brilliant (SRB) is the most common example, typically using 57 or 58 facets.

Cabochon

A gemstone shaped and polished into a smooth, rounded dome rather than faceted.Cabochons are often used for opaque or translucent stones, or those displaying optical phenomena like chatoyancy or asterism.

CAM (Computer Aided Meetpoint)

A faceting technique where facet positions are calculated so that edges meet precisely at planned points.CAM designs use mathematical precision to ensure all facet junctions align perfectly, producing clean meetpoints without trial and error.

Cheater

A fine adjustment mechanism on a faceting machine that allows small rotational corrections to achieve precise meetpoints after transfer.Its purpose is corrective, not creative: when a stone is transferred to a second dop it rarely lands in perfect register with the first, and the cheater dials out that residual error by rotating the whole index a fraction of a position. Because the offset is a fraction rather than a whole step, it also resolves tiers whose geometry falls between the gear's fixed positions — stepped crowns and elongated tables being the usual cases.

Checker crown

A crown cutting style using alternating angled facets that create a checkerboard-like pattern when viewed from above.Checker crowns add visual complexity with relatively few facets. The alternating angles catch light from different directions, producing lively scintillation.

Critical angle

The minimum angle at which light inside a gemstone is totally internally reflected rather than escaping.Measured from the facet normal, not from the girdle plane your machine protractor reads — the two conventions differ by about 17° for diamond. It is a floor, not a working angle: a pavilion main below it windows, but real designs sit well above it, because light must reflect twice and still exit through the crown. Diamond pavilion mains run around 41° on the protractor. Set by the refractive index: 24.4° for diamond, 40.4° for quartz.

Crown

The upper portion of a faceted gemstone, above the girdle.The crown contains the table facet, star facets, bezel (kite) facets, and upper girdle facets in a standard brilliant cut.

Culet

The bottom point or small facet at the base of the pavilion.In most modern cuts, the culet comes to a sharp point. Some older cuts feature a small polished facet at the culet to prevent chipping.

Depth ratio

The total depth of a finished stone expressed as a percentage of its girdle width.Depth ratio affects brilliance and appearance. Typical values range from 55% to 75% depending on the cut style and material.

Dispersion

The splitting of white light into spectral colors as it passes through a gemstone.Higher dispersion values produce more visible 'fire.' Diamond has a dispersion of 0.044, while materials like sphene (0.051) and demantoid garnet (0.057) show even more fire.

Dop

A holder that secures the gemstone to the faceting machine mast during cutting.Dops can use wax (for heat-sensitive stones), cyanoacrylate adhesive, or mechanical clamping. Accurate dopping is critical for symmetry.

Dopping

The process of attaching a gemstone to a dop stick for faceting, using wax, adhesive, or mechanical clamping.Everything downstream inherits the dop's alignment, so a stone seated even slightly off-axis will never cut symmetrically no matter how carefully the angles are dialled. Contact area governs how much shear the joint survives; any oil or polishing residue at the interface prevents the adhesive keying to the stone; and most adhesives need many hours to reach full strength, so a joint that feels solid can still creep under load. Dopping faults account for a large share of symmetry problems that get blamed on the machine.

Double refraction

A property of some gemstones where a single ray of light splits into two rays traveling at different speeds through the crystal.Measured as the difference between the highest and lowest refractive indices. High double refraction (e.g., zircon at 0.059) can cause visible facet doubling when viewed through the stone.

Facet

A flat, polished surface on a gemstone.Each facet is defined by its angle from the horizontal plane (mast angle) and its rotational position (index setting).

FCP (Final center point)

The permanent center point at the base of the pavilion, formed by the main pavilion facets converging at a single point.The FCP is the first feature cut on most designs and serves as the foundation for all subsequent facets. Take care to form it perfectly, as errors propagate through the entire stone.

Fire

Visible spectral colors produced by light dispersion within a gemstone.Fire is most visible in materials with high dispersion. Crown angles significantly affect fire; shallower crowns tend to show more fire.

Float-in

A faceting technique where a facet is positioned by visual judgment rather than meeting specific geometric points.The design gives no meetpoint target to cut to, so the cutter judges depth by eye against the drawn proportion and stops when it looks right. Tables and decorative tiers are the usual candidates, because there the eye reads proportion long before it reads a geometric error.

Frosting

The intentional textured finish of one or more facets on a faceted gemstone, used to create decorative patterns.Achieved using a worn coarse lap (e.g., 800 grit bronze sintered). The frosted finish contrasts with polished facets to create visual patterns. Cut frosted facets very slowly and check with a hand lens.

Girdle

The outer edge or band around the widest part of a faceted gemstone, separating the crown from the pavilion.Girdle thickness is typically expressed as a percentage of the stone's width. A girdle that is too thin risks chipping; too thick wastes material.

Index gear

A notched wheel on the faceting machine that controls the rotational position of the stone for each facet.Common gear sizes include 64, 72, 80, and 96 teeth. The number of teeth determines which rotational positions are available. A 96-index gear provides the finest control.

Kerf

The width of material removed by a saw blade when cutting rough gemstone material.Minimizing kerf is important for maximizing yield from expensive rough. Diamond saws produce narrower kerfs than other types.

L/W ratio

The length-to-width ratio of a gemstone, describing its outline shape.A 1.0 ratio indicates a round or square stone. Ovals typically range from 1.3 to 1.5, while marquises range from 1.75 to 2.25.

Lap

A flat rotating disc used to grind and polish facets on a gemstone.Laps come in various materials: copper or cast iron for cutting, tin or ceramic for pre-polishing, and specially charged laps for final polishing. Never skip laps in the grit progression -- each lap removes scratches from the previous one.

Lap progression

The sequence of increasingly fine laps used to take a facet from rough cutting to final polish.A typical progression: 260 grit (shaping) -> 600 grit (smoothing) -> 1200 grit (pre-polish) -> 3000+ grit (polish). Skipping grits can wear out laps faster and make polishing much harder.

Mast angle

The angle between the lap surface and the facet being cut, set on the faceting machine's protractor.Mast angles are measured from 0 (horizontal/parallel to lap) to 90 degrees (perpendicular to lap). The table facet is always at 0 degrees.

Meetpoint

A point where three or more facet edges converge precisely.A meet that misses tells you the angle, the index or the depth was off, so meetpoints double as the cutter's error signal — they are how a fault is caught while it can still be corrected. Visually, a missed meet leaves a sliver facet or a rounded junction that catches light differently from its neighbours, which is why poor meets read as untidy long before anyone measures them.

Pavilion

The lower portion of a faceted gemstone, below the girdle.Pavilion angles are critical for light return. Angles below the critical angle cause light to leak through the bottom (windowing).

Portuguese cut

A faceting style with multiple tiers of facets, producing exceptional brilliance and fire.Portuguese cuts typically have 3-5 rows of facets on both the crown and pavilion. They yield excellent light performance but require more cutting time.

Preform

A rough gemstone that has been shaped to approximate the final design before precision faceting begins.Bulk material comes off far faster on a coarse lap than it does during faceting proper, so roughing the outline first keeps the slow, precise work confined to the last fraction of a millimetre. It also exposes the stone's inclusions and colour zoning early, while there is still freedom to shift the design.

Refractive index

A measure of how much light slows and bends when entering a gemstone material.Higher RI materials bend light more and have a LOWER critical angle, which widens the range of pavilion angles that return light instead of leaking it. Quartz has an RI of 1.544 (critical angle 40.4°), while diamond is 2.417 (24.4°).

RI optimization

The practice of adjusting cutting angles for a design based on the refractive index of the specific material being cut.Many designs provide multiple angle sets (A, B, C) optimized for different RI ranges. Using the correct set maximizes brightness and prevents light leakage. For example, Set A might cover quartz (RI 1.54), while Set B covers sapphire (RI 1.77).

Rose cut

A historic faceting style with a flat base and a domed top covered in triangular facets.Rose cuts date to the 16th century and have seen a revival in modern jewelry. They lack a pavilion, producing a different light performance than brilliant cuts.

Rough

Uncut, natural gemstone material as it comes from the mine or source.Evaluating rough involves assessing clarity, color distribution, crystal shape, and potential yield for different cutting designs.

Scintillation

The pattern of light and dark areas visible when a gemstone, the light source, or the viewer moves.Good scintillation produces a lively, sparkling appearance. It depends on facet size, symmetry, and the number of virtual facets created by internal reflections.

Step cut

A faceting style using rectangular facets arranged in parallel rows, like stair steps.The emerald cut is the most well-known step cut. Step cuts emphasize clarity and color over brilliance, producing broad flashes of light ('hall of mirrors' effect).

Symmetry

The precision with which corresponding facets are uniformly shaped, sized, and positioned.Symmetry is graded in gem cutting competitions and commercial grading. Poor symmetry degrades light performance even when angles are correct.

Table

The large, flat facet on top of a faceted gemstone.Table size is expressed as a percentage of the girdle width. For brilliant cuts, typical table percentages range from 50% to 65%.

Table percentage

The width of the table facet expressed as a percentage of the total girdle width.Larger tables increase brilliance but reduce fire. Smaller tables enhance fire and scintillation. The optimal percentage varies by material and design.

TCP (Temporary center point)

A temporary convergence point formed during preforming that gets cut away as the final pavilion facets are added.TCPs are used in preform-based cutting sequences to establish a rough girdle outline. Unlike the FCP, the TCP is deliberately removed -- you cut away the TCP, not meet it.

Tier

A row or level of facets on the crown or pavilion of a gemstone.Standard brilliant cuts have 2-3 tiers per section. More complex designs like Portuguese cuts may have 5 or more tiers.

Transfer

The process of removing a stone from one dop and re-mounting it on another to cut the opposite side (typically switching from pavilion to crown).Accurate transfer is critical. If the transfer is off, crown facets won't align properly with the pavilion. Use the cheater (fine adjustment) after transfer to correct any misalignment before cutting crown facets.

Windowing

A transparency defect where light passes straight through the pavilion instead of reflecting back to the viewer, creating a see-through area.Caused by pavilion angles cut below the critical angle for the material. Higher RI materials have lower critical angles and are less prone to windowing. Always check that your pavilion main angle exceeds the critical angle.

Yield

The percentage of the original rough stone weight retained in the finished faceted gem.Typical yields range from 25% to 50%. Maximizing yield while maintaining optical performance is a key consideration in design selection.