The key to a successful polish lies in meticulous preparation—you must completely remove the scratches left by each coarser abrasive before moving to the next.
The Lapidary Process: Step-by-Step
The complete journey from rough stone to finished gem typically involves six core stages.
1. Preparation and Planning (The Rough)
The first step is a critical evaluation of the rough stone. A gem cutter (or lapidist) must plan the cut to maximize the stone’s beauty and weight retention while eliminating or hiding internal flaws.
Determine Orientation: Examine the stone to find its most appealing color, identify any color banding or zoning, and locate large inclusions (flaws) or fractures that must be cut away.
Select Cut Type: Decide whether the stone will be a Faceted Gem (precise, flat surfaces for brilliance, ideal for transparent stones like sapphire) or a Cabochon (a smooth, domed surface, often used for opaque or patterned stones like turquoise).
Sawing: Use a diamond-tipped saw blade (lubricated with water or oil to prevent overheating) to slice the rough material. This removes waste, eliminates large flaws, and creates a manageable preform (basic shape).
2. Preshaping and Grinding
This stage creates the foundational shape of the gem.
Grinding: Using coarse-grit diamond wheels or laps (flat, rotating discs), the cutter grinds the preform to its approximate final dimensions.
For cabochons, the rough corners are removed, and the dome and base shapes begin to take form.
For faceted stones, the cutter establishes the initial angles for the pavilion (the bottom cone) and crown (the top).
Dopping: The preformed stone is affixed to a metal rod called a dop using specialized dopping wax or glue. The dop acts as a handle, allowing the cutter to hold and manipulate the stone precisely during the intricate faceting and polishing steps.
3. Faceting (For Brilliant Cuts)
Faceting is the highly skilled process of cutting precise, flat surfaces, or facets, onto the gem to maximize light return.
Machine Setup: A faceting machine is used, allowing the cutter to set and control three crucial variables for each facet:
Index Gear: Controls the rotation of the stone, determining the position of the facet around the stone’s edge.
Angle Setting: Controls the angle at which the facet is cut relative to the table (the top surface). This angle is crucial for the stone’s brilliance; if the pavilion is cut too deep or too shallow, light will leak out, creating a dull “window”.
Depth Control: Determines how deep each facet is cut.
Cutting: The cutter systematically applies the dopped stone to progressively finer diamond-impregnated laps, working through the pavilion, girdle (edge), and crown facets.
4. Sanding and Pre-Polishing
This stage focuses on removing the deep scratches left by the coarse grinding tools.
Finer Grits: The gem is subjected to progressively finer abrasives, moving from around 220 grit up to 600 or 1200 grit.
The Goal: The goal is to create a perfectly smooth, uniform surface that appears matte or “fuzzy-polished,” but is free of any scratches visible to the naked eye. Pre-polishing is the most critical step; any deep scratches remaining at this stage will prevent the final mirror-like finish.
5. Final Polishing
The final stage is where the gem’s true luster is revealed.
Polishing Agents: The stone is worked against a polishing lap (which may be tin, ceramic, or a fabric/felt wheel) loaded with an ultra-fine abrasive, such as diamond paste (e.g., 50,000 to 100,000 grit) or an oxide polish (like cerium oxide or alumina).
Technique: The cutter uses very light pressure and a continuous supply of lubricant (water or oil). The chemical and mechanical action of the polishing agent removes the microscopic scratches from the pre-polish stage, giving the gem its signature mirror-like shine and maximizing its optical performance.
6. Clean and De-Dop
Once the polish is complete, the stone is carefully removed from the dop stick (often by gently heating the wax) and cleaned thoroughly to remove all traces of wax, oil, and polishing compound, leaving a finished, sparkling gemstone.