Compound classes
Polishing compounds used in lapidary practice fall into four principal classes: metal-oxide compounds, metallic alloys, diamond pastes and slurries, and adhesive sheets.
Metal-oxide compounds
Cerium oxide is the dominant final-polish compound for quartz-family material and many softer silicates. It is supplied as a fine powder, prepared as an aqueous slurry, and applied to a felt or leather buff or to a master lap.
Aluminum oxide and tin oxide are alternatives positioned for specific species. Tin oxide produces a slightly different surface finish on tourmaline and is preferred by some cutters for the transition between pre-polish and final polish.
Oxide compounds are inert under normal shop conditions; a material safety data sheet accompanies each compound at time of purchase.
Metallic alloys
Tin-lead alloys, applied to a master lap, produce a soft polishing surface that retains diamond charging. The compound is melted onto the master lap and worked into the surface; the charged plate is then used as a polish lap. Tin-lead master plates are commonly used at 50,000 mesh and finer.
Diamond pastes and slurries
Diamond pastes are supplied in graduated grits from 14,000 mesh through 100,000 mesh and finer. The carrier is typically water-soluble; a 5-gram syringe is the standard format. Diamond slurries — looser preparations — are used in the same grit range and are applied with a brush or dropper.
Diamond compounds are applied to phenolic, ceramic, or composite polishing buffs. The grit position of the compound on the manufacturer's grit ladder establishes its place in the polishing workflow.
Adhesive sheets
Adhesive PET sheets — the Spectra Ultralap product family — are diamond-coated single-use polishing sheets. They are applied to a master lap and replaced periodically as their cutting effectiveness diminishes. Common grits in this format are 8,000, 14,000, 50,000, and 100,000 mesh.
Choice of compound
The choice of compound is species-dependent and is documented in the faceting literature for each gem species. Cerium oxide is general-purpose; tin oxide is a tourmaline-specific alternative; tin-lead alloy with diamond charging is a connoisseur-tier finish for corundum and topaz.