Cutting Techniques

The most common cutting style for opaque and translucent gems: What is a Cabochon: A gem cut with a smooth, rounded, convex top and usually a flat bottom. The name comes from the French "caboche" meaning "head," referring to the rounded shape. Best Materials: Cabochons are ideal for opaque gems (jasper, agate, turquoise), gems with phenomena (star sapphire, cat's eye), or materials with inclusions that would show in faceted cuts. They showcase color, patterns, and optical effects. Cutting Process: 1. Select and mark the rough to determine the best orientation 2. Saw to approximate size and shape 3. Grind the bottom flat 4. Shape the top using progressively finer wheels 5. Sand to remove scratches 6. Polish to mirror finish Shapes: Common cabochon shapes include oval (most popular), round, square, rectangular, and freeform. The shape should complement the material's natural patterns. Proportions: Standard cabochons have a dome height of about 50-60% of the width. Higher domes (tall cabs) create more depth but may be harder to set in jewelry. Specialty Cabs: Double cabs (domed on both sides), flat cabs (minimal dome), and carved cabs (with additional decorative carving) offer variety.

Creating flat surfaces (facets) that reflect and refract light: Purpose: Faceting maximizes a gem's brilliance, fire (color dispersion), and scintillation (sparkle). It's used primarily for transparent gems. Facet Types: - Crown Facets: The top portion above the girdle. Includes table (large top facet), star facets, bezel facets, and upper girdle facets. - Pavilion Facets: The bottom portion below the girdle. Includes main pavilion facets, lower girdle facets, and culet (bottom point). - Girdle: The widest part, separating crown and pavilion. Cutting Process: 1. Preform the rough into approximate shape 2. Cut the pavilion facets first (working from bottom up) 3. Flip and cut the crown facets 4. Polish all facets to mirror finish 5. Final inspection and adjustments Precision Required: Faceting demands extreme precision. Angles must be exact (within 0.1-0.2 degrees) for optimal light performance. Modern faceting machines provide this precision. Popular Faceted Cuts: Round brilliant (most popular for diamonds), princess (square), emerald cut (rectangular with step facets), oval, pear, marquise, and many others. Each has unique characteristics. Light Performance: Well-cut faceted gems return maximum light to the viewer's eye. Poor cuts leak light out the bottom, making gems appear dark.

Initial shaping of rough material: Slabbing: Cutting large rough into thin slices using a diamond saw. Essential for materials like agate, jasper, and petrified wood. Allows you to see internal patterns and plan cuts. Trimming: Removing unwanted material and rough edges. Can be done with a trim saw (small saw) or by grinding. Creates a manageable size for further work. Preforming: Shaping the rough into a form close to the final shape. For cabochons, this means creating the basic oval or round shape. For faceted gems, creating a cone or other basic form. Equipment: Various saws are used: - Slab Saw: Large saw with diamond blade for cutting thick slabs - Trim Saw: Smaller saw for precise cuts and trimming - Band Saw: For freeform cutting and irregular shapes Coolant: Water or specialized cutting fluid keeps the blade cool and removes debris. Essential for preventing blade damage and material cracking. Safety: Always use eye protection, keep hands away from blades, and ensure proper machine guards. Diamond saws can cause serious injury if mishandled.

Advanced and specialized cutting methods: Inlay Work: Cutting pieces to fit precisely into recessed areas. Used in jewelry, decorative objects, and artistic pieces. Requires extreme precision and patience. Intarsia: Creating pictures or patterns by cutting and fitting together different colored stones. Like a jigsaw puzzle in stone. Requires careful planning and precise cutting. Carving: Three-dimensional sculpting of gems. Creates figurines, cameos (raised design), intaglios (recessed design), and decorative objects. Requires artistic skill and specialized tools. Freeform Cutting: Following the natural shape of rough to minimize waste. Creates unique, organic shapes. Popular for one-of-a-kind pieces and artistic expression. Calibrated Sizing: Cutting gems to standard sizes that fit common jewelry settings. Makes replacement and setting easier. Requires precision and knowledge of standard sizes. Recutting: Improving poorly cut gems by recutting them. Can significantly improve appearance and value, though some weight is lost. Requires identifying the best new cut for the material.

Different materials require different approaches: Hardness: Harder materials (like sapphire, 9 on Mohs scale) require diamond tools and more time. Softer materials (like opal, 5.5-6.5) cut faster but require more care to avoid damage. Fracture and Cleavage: Materials with perfect cleavage (like topaz) can split along cleavage planes if not handled carefully. Must orient cuts to avoid these planes. Heat Sensitivity: Some materials (like opal) can crack if they get too hot during cutting. Must use plenty of coolant and avoid excessive pressure. Inclusions: Materials with many inclusions may be better suited for cabochons than faceting. Inclusions can weaken faceted gems and create weak points. Color Zoning: Materials with uneven color distribution require careful orientation to maximize color in the finished piece. Size and Shape: The natural shape of rough determines what cuts are possible. Large, well-shaped pieces allow more options. Small or irregular pieces may be limited to specific cuts. Value Considerations: For valuable materials, maximizing yield (finished weight) is important. Sometimes accepting a less-than-ideal cut preserves more material value.

Essential equipment for cutting: Faceting Machine: Precision machine for cutting facets. Consists of a mast (vertical post), dop (holder for gem), and lap (cutting/polishing surface). Allows precise angle and index control. Cabochon Machine: Vertical or horizontal grinding/polishing machine. Has multiple wheels of different grits for shaping and polishing. Some have expandable drums for different sizes. Diamond Saws: Various sizes for different tasks. Blades are embedded with diamond particles for cutting hard materials. Require water cooling. Laps: Flat disks used for cutting and polishing. Different materials (diamond, silicon carbide, cerium oxide) for different stages and materials. Dops: Holders that secure gems during cutting. Can be mechanical (screws) or wax-based. Must hold securely without damaging the gem. Measuring Tools: Calipers for measuring dimensions, protractors for angles, and loupes for inspection. Precision is essential for quality work. Safety Equipment: Eye protection, dust masks, and proper ventilation. Some materials create harmful dust when cut.