A diamond pellet — also known as a diamond charging pellet — is a small, compressed tablet of bonded diamond abrasive used to charge the surface of metal faceting laps, most commonly those made from cast iron or copper. Rather than applying loose diamond powder or spray directly to a rotating lap, the operator presses a pellet of the appropriate grit against the lap surface under light, controlled pressure; the rotation of the lap causes the diamond particles to embed uniformly into the softer metal matrix, creating a charged cutting or polishing surface. Diamond pellets occupy an important place in the modern lapidary workshop as a cleaner and more repeatable alternative to traditional loose-grit charging methods.

Construction and Grit Grades

Pellets are manufactured by compressing micron-graded synthetic diamond powder, typically together with a binder that holds the tablet together during storage and handling but releases the abrasive progressively under the friction of charging. They are produced across a wide range of mesh sizes to suit every stage of the faceting sequence. Coarser grades — commonly 260 to 600 mesh — are used for rough shaping and pre-forming; mid-range grades such as 1,200 and 1,800 mesh serve the pre-polish stage; and fine grades of 3,000 mesh and above, including 8,000 and 14,000 mesh, are employed for final polish on laps intended for hard gem materials such as corundum, chrysoberyl, and diamond itself. Suppliers including Crystalite and the United States Faceters Guild (USFG) have offered pellets in standardised grit increments, allowing faceters to build a consistent, step-by-step progression through the cutting and polishing sequence.

Charging Procedure

To charge a lap, the faceter starts the lap spinning at a moderate speed and holds the pellet flat against the surface, applying gentle downward pressure and moving the pellet in a slow, overlapping spiral from the inner radius toward the outer edge. The pellet wears away as diamond particles transfer into the metal. A single pellet is typically sufficient to charge one lap for a working session, though heavily grooved or worn laps may require additional passes. Once charging is complete, a small amount of lubricant — water, a water-soluble cutting fluid, or a dedicated lap lubricant — is applied before cutting begins. The charged lap can be re-used across multiple sessions; the surface is recharged as the embedded diamond becomes depleted, indicated by a reduction in cutting speed or an increase in scratching on the stone.

Advantages Over Loose Diamond

The principal advantage of the pellet format is contamination control. In a faceting workshop where several laps of different grit sizes may be in use, accidental cross-contamination — coarser particles migrating onto a fine-polish lap — is a persistent risk with loose powders and sprays. Because a pellet delivers its diamond charge in a single, contained operation and is then fully consumed or set aside, the risk of transferring abrasive between laps is substantially reduced. Pellets also eliminate the need for precise measurement of loose powder, reduce waste, and simplify storage, since each pellet is individually packaged or stored in a labelled vial corresponding to its grit grade. For travelling faceters or those working in limited bench space, the compact format is a practical convenience.

Limitations and Considerations

Diamond pellets are a consumable: each charging session depletes the pellet, and a stock of multiple grit grades must be maintained. The cost per session is generally higher than an equivalent quantity of loose diamond powder, though the reduction in waste and contamination often offsets this for serious hobbyists and professional faceters alike. Pellets are most effective on laps with a relatively smooth, flat surface; heavily scored or pitted laps may charge unevenly, leaving areas of the surface under-loaded with abrasive. Some faceters also note that very fine-grit pellets (above 8,000 mesh) can be more difficult to charge evenly than their coarser counterparts, and may benefit from a slower lap speed and lighter pressure during application.

In the Trade

Diamond pellets are stocked by specialist lapidary suppliers and are a standard consumable in the inventories of faceting clubs and guild suppliers. They are sold individually or in sets covering a complete grit progression. When selecting pellets, faceters should match the grit grade to the specific lap material: cast-iron laps accept diamond charging readily and are the most common substrate, while copper laps, used for certain ultra-fine polishing applications, may require a lighter charging pressure to avoid over-embedding coarser particles. Tin and typemetal laps, occasionally used for oxide polishing, are generally not charged with diamond pellets and fall outside the intended application of this product.