A diamond charging stick is a solid bar or rod of bonded diamond abrasive used in faceting and lapidary polishing to embed — or charge — diamond particles into the surface of a metal or composite lap. By pressing the stick against a rotating lap, the operator transfers a controlled layer of diamond grit that then performs the actual cutting or polishing of the gemstone. The charging stick is a traditional and widely trusted method for maintaining the cutting efficiency of laps that do not carry a factory-applied abrasive coating.

How Charging Works

Metal laps — most commonly cast iron, copper, or tin — are inherently soft enough to accept and retain abrasive particles within their surface. When a charging stick is held against the rotating lap under moderate pressure, the diamond grains are progressively pressed into the lap matrix, creating a fine, evenly distributed cutting surface. The process is sometimes supplemented with a small quantity of lubricant, such as a light oil or a dedicated lap extender fluid, to help distribute the grit uniformly and prevent the stick from glazing the lap surface rather than charging it.

Charging is typically performed at the start of a polishing session and repeated as the lap's cutting action diminishes. An experienced facetor can judge when recharging is needed by the feel of the lap against the stone and by the rate at which material is being removed.

Grit Range and Applications

Diamond charging sticks are manufactured across a wide spectrum of grits, from coarser grades around 600 mesh — used for pre-polishing and shaping on softer materials — through to very fine grades of 50,000 mesh or finer (approaching 0.1 micron), used for final polishing of hard gemstones such as corundum, spinel, and chrysoberyl. The selection of grit is matched to the stage of the cutting sequence and to the hardness of the material being worked:

• 600–3,000 mesh: Pre-polish and scratch removal on hard stones; general cutting on softer materials.
• 8,000–14,000 mesh: Pre-polish on corundum and other species above Mohs 8; polish on softer stones.
• 50,000–100,000 mesh: Final polish on corundum, spinel, and other hard gemstones where a mirror finish is required.

Lap Compatibility

Not every lap type is suited to charging with a stick. The method is most effective with:

• Cast-iron laps: The traditional choice, particularly for corundum polishing; the relatively soft iron matrix holds diamond grit tenaciously.
• Copper laps: Widely used for intermediate polishing stages; copper's malleability allows good grit retention.
• Tin laps: Preferred by many facetors for final polishing of very hard stones; tin yields an exceptionally fine, consistent charged surface.
• Composite and alloy laps: Some proprietary blended-metal laps are also designed to accept charging.

Resin-bond, ceramic, and pre-plated diamond laps are generally not charged with a stick, as their surfaces are either too hard to accept embedded grit or already carry a fixed abrasive layer.

In the Trade and Among Facetors

The United States Faceters Guild and standard lapidary references treat the charging stick as an established consumable in the serious facetor's toolkit. Its appeal lies in economy and control: a single stick of a given grit can charge a lap many times over, and the facetor can vary the density of the charge by adjusting pressure and the number of passes. This degree of control is valued when polishing difficult or inclusion-prone stones where an overly aggressive surface could cause chipping along facet junctions.

Charging sticks are available from specialist lapidary suppliers in various diameters and lengths; smaller-diameter sticks allow more precise placement of grit on a specific zone of the lap, which is occasionally useful when only part of a lap's surface requires refreshing. Storage is straightforward — the sticks are robust and do not degrade if kept dry and free of contamination from coarser abrasives.