Amplex diamond compound is a range of graded diamond polishing pastes manufactured under the Amplex brand, a product line of Saint-Gobain Abrasives, one of the world's principal producers of synthetic abrasive and superabrasive materials. The compound suspends synthetic diamond particles of controlled size within a carrier medium — typically a wax or oil-based paste — and is applied to laps, polishing wheels, or felt buffs to achieve high-polish finishes on gemstones, ceramics, carbides, and other hard or precision-ground materials. In lapidary practice, Amplex is regarded as a consistent and reliable choice for the final polishing stages of faceted stones and cabochons.

Composition and Grading

The defining characteristic of any diamond compound is the nominal particle size of its abrasive fraction, expressed in microns (µm). Amplex compounds are available across a broad spectrum of grades, from relatively coarse formulations used for stock removal or pre-polishing through to ultra-fine grades intended for final mirror finishes. Common grades encountered in lapidary supply catalogues include 14 µm, 8 µm, 3 µm, 1 µm, and sub-micron preparations. The lower the micron value, the finer the scratch pattern left on the workpiece and, consequently, the higher the resulting surface lustre.

The carrier medium serves several functions: it keeps the diamond particles in suspension, provides lubrication between the lap and the stone, and controls the rate at which compound is delivered to the working surface. Amplex pastes are formulated to remain stable across the temperature ranges typical of lapidary work, resisting separation of the diamond fraction from the carrier during use.

Application in Lapidary Practice

In gemstone polishing, Amplex compound is most commonly applied to a charged lap — a flat or domed disc of metal, wood, leather, or felt — by spreading a small quantity of paste across the surface before or during the polishing run. The choice of lap material interacts closely with the compound grade: a tin or typemetal lap charged with a fine diamond compound is a standard approach for polishing faceted quartz, topaz, and many other species, while felt or leather buffs charged with sub-micron compound are preferred for the final stages on softer or more sensitive materials.

Grade selection is critical. Using too coarse a compound at the final polishing stage will leave visible scratches, particularly on stones with a Mohs hardness below 7 or on cleavage-prone species such as topaz and fluorite. Conversely, beginning the polishing sequence with an excessively fine grade on a stone that still carries pre-polish scratches will be inefficient and may produce a hazy rather than a sharp polish. Standard lapidary practice calls for a progressive sequence: pre-polish with a medium grade, then final polish with a fine or ultra-fine grade, cleaning the lap and the stone thoroughly between stages to prevent cross-contamination of grit sizes.

Industrial and Precision-Optical Context

Beyond the lapidary workshop, Amplex and comparable diamond compounds from Saint-Gobain are used extensively in precision optical grinding, semiconductor wafer preparation, and the finishing of cemented carbide tooling. The same principles of particle-size control and carrier chemistry apply in these industrial contexts, though the tolerances demanded are often considerably tighter than those required for decorative gemstone work. This industrial heritage underpins the consistency that lapidary users value: Amplex compounds are manufactured to engineering standards, with particle-size distributions that are tightly controlled by sieving or centrifugal classification.

Practical Considerations

• Contamination control: Diamond compound must be kept scrupulously free of coarser abrasive particles. Dedicated laps, separate containers, and careful workshop hygiene are essential when working through a polishing sequence.
• Economy of use: Diamond compound is effective in very small quantities. Overloading a lap wastes material and can produce uneven results as excess paste accumulates at the edges of the workpiece.
• Storage: Pastes should be stored with caps tightly closed to prevent the carrier from drying out or oxidising, which can alter the consistency and performance of the compound.
• Compatibility: While diamond is the hardest abrasive available and is in principle suitable for any gemstone material, the choice of carrier and lap must be matched to the stone species; some carriers may stain porous or included stones.

Amplex diamond compound occupies a well-established position in the lapidary supply trade as a dependable, professionally manufactured product. Its availability in a logical progression of micron grades makes it straightforward to build a coherent polishing sequence, and its provenance within a major industrial abrasives group provides a degree of quality assurance not always present in smaller or less standardised diamond paste products.