Modern gem cutting combines old principles with new machines. Cutters still grind and polish with abrasives harder than the stone, and diamond powder is still the main abrasive. What has changed is control. Faceting machines hold angles to a fraction of a degree, lasers saw diamonds along planned paths, 3D scanners map rough before the first cut, and software predicts which plan will give the most value.
Faceting machines for colored stones
A faceting machine has three main parts: a flat, spinning lap charged with abrasive, a mast that holds the stone, and a handpiece called the quill. The stone is glued to a metal rod (a dop) clamped in the quill. An angle protractor sets the facet angle, and an index gear sets the rotation around the stone, often divided into 96 or 120 steps. A depth stop tells the cutter when a facet reaches its target.
Laps are made in a range of grits. Coarse laps, often with sintered or plated diamond, shape the stone quickly. Finer laps refine the facets. Polishing laps of materials such as tin, ceramic, copper, zinc or composite, charged with very fine diamond, cerium oxide or aluminum oxide, bring the facets to a mirror finish. Different gems prefer different polishing laps and compounds, and cutters learn these pairings through experience.
With these machines a cutter can follow a faceting diagram, a printed plan giving each facet's angle and index setting, and reproduce a design closely. Many professional cutters in colored stone centers still use simpler jamb peg setups, where the angle is set by placing the dop stick into holes in a wooden block. Those cutters work fast and judge angles by eye and feel.
Planning and 3D scanning
Rough gems are expensive, so planning has a large effect on value. For diamonds, scanning systems photograph the rough from many angles or use lasers to build a 3D model. Some systems also map inclusions inside the stone. Planning software then tries many possible cuts, comparing shapes, sizes and clarity outcomes, and suggests the combination that should give the best mix of weight and quality.
A planner reviews these options and marks the chosen sawing and cutting lines. For colored stones, scanning helps too, but color, color zoning and pleochroism are harder to model, so the cutter's judgment carries more weight. Cutters orient a ruby or tourmaline to show its best color face-up, which software models only partly.
Laser sawing and shaping
Before lasers, diamonds were split along cleavage planes with a blade or sawn with a thin phosphor bronze blade charged with diamond powder, which could take hours or days per stone. Lasers changed this. Pulsed lasers vaporize a narrow path through a diamond, and green or infrared lasers are common. A laser can saw in any direction, including across grain directions that a blade would struggle with.
Lasers also shape rough into round blanks, a step called laser bruting or laser girdling, and cut fancy shapes with less waste. Laser sawing of very large rough is often done in stages with careful cooling. Lasers are used for laser inscription too, writing a report number or brand mark on a diamond's girdle in letters visible only under magnification.
Waterjet-guided lasers, which carry the laser beam inside a thin water stream, reduce heat damage and leave cleaner cuts. Some colored stone cutters use lasers for sawing, though wire and blade saws remain common for most colored rough.
Automated polishing
Small diamonds, called melee, are cut in very large numbers. Automated polishing machines hold many stones at once and polish facets with little human input. Mechanical arms and sensors keep the angles consistent. These machines made the mass production of small diamonds practical, especially in cutting centers in India such as Surat, as described on the diamond pipeline page.
Larger and better stones still pass through skilled hands for final polishing, but many cutters use machines that hold the stone at exact angles while the cutter controls pressure and timing.
Precision cutting and cut grading
Better tools and measuring devices allowed tighter proportions. Optical scanners measure a finished diamond's table size, crown and pavilion angles and girdle thickness to fine tolerances. These measurements feed the cut grades used by major labs for round brilliants. Cutters aiming for an "excellent" or "ideal" grade can check a stone during cutting and correct it. The round brilliant cut page explains these proportions.
For colored stones, precision cutting usually means sharp facet junctions, even facets, a well-shaped outline and good light return. Precision cutters often recut commercial stones from gem-producing countries, which may have been cut to save weight instead of for the brightest result.
CNC carving and ultrasonic drilling
Computer numerical control (CNC) machines follow digital designs. Carvers use CNC tools with diamond burrs to rough out cameos, figurines and beads in hardstone, and a human carver often finishes the detail. CNC cutting also makes it possible to repeat the same carved shape many times.
Ultrasonic drilling uses a tool that vibrates many thousands of times per second against the stone, with an abrasive slurry between them. It can drill round holes and cut shapes in hard, brittle materials like jade, agate and corundum without much pressure. Bead drilling also uses diamond-coated drill bits on fast rotary tools, cooled with water.
Concave and fantasy cutting
New tools have opened new styles. Concave faceting uses cylinder-shaped laps to grind curved, scooped facets that throw back extra light. Fantasy cuts, developed from the 1960s onward by German cutters such as Bernd Munsteiner, combine carved grooves and flat facets on the back of a stone. These styles appear on the gem cut shapes and styles page.
Workshop safety
Cutting raises dust, and some gem materials are harmful when inhaled. Malachite dust contains copper, and quartz dust can cause lung disease over time. Wet cutting, water-cooled laps and dust extraction reduce these risks. Lasers need shielding and eye protection.
Frequently asked questions
Do diamond cutters still cut by hand?
Many steps are now automated or laser-assisted, especially for small stones, but skilled cutters still plan, check and polish larger and higher-quality diamonds by hand.
What does a faceting machine do?
It holds the stone at a precise angle and rotation against a spinning abrasive lap, so a cutter can grind and polish each facet to a planned design.
How do lasers cut diamonds?
Pulsed lasers vaporize a narrow path of carbon through the diamond. They can saw in any direction and shape rough into round or fancy outlines.
What is laser inscription?
A laser writes a tiny report number or mark on the girdle of a diamond. It is visible only with magnification and helps match the stone to its grading report.