Polishing Compound — Graded Abrasives for Bench and Lap
Polishing Compound — Graded Abrasives for Bench and Lap
The pastes and bars that take metals and gemstones from cut to mirror finish
Polishing compound is the abrasive paste, bar, or pellet applied to a buffing wheel, mop, lap, or pad to refine a metal or gemstone surface. Compounds are graded by abrasive particle size and chemistry, and the choice of compound at each finishing stage is what separates a working surface from a presentation finish. The bench jeweller, the silversmith, and the lapidary each carry their own short list of compounds, sequenced from coarse cut-down to final polish.
Composition and grading
Most polishing compounds are mixtures of an abrasive powder and a wax or grease binder pressed into a bar or worked into a paste. The abrasive does the work; the binder carries it onto the wheel and controls the rate at which it transfers to the work. Common bench-jeweller abrasives include tripoli, a coarse silica earth used for initial smoothing of cast or fabricated gold and silver; rouge, a fine ferric-oxide compound used for the final lustre on precious metal; and chromium oxide, a green compound used on harder alloys and on stainless steel. Diamond compounds, supplied in graded micron sizes from roughly 50 µm down to 0.25 µm, are used where the work demands hardness or precision beyond conventional oxides — platinum, hardened steel, ceramic, and gemstone material.
Lapidary compounds are dominated by cerium oxide for quartz, beryl, and feldspar, aluminium oxide for harder species, tin oxide for selected softer materials, and diamond for corundum, spinel, and other hard stones. Each is matched to a lap material — copper, tin, zinc, ceramic, phenolic — chosen for its ability to retain the abrasive and present it to the facet at the correct firmness.
Sequencing
Bench finishing typically runs tripoli on one spindle for cut-down, then rouge on a separate spindle for the final pass, with the wheels kept apart so coarse abrasive does not contaminate the final-stage mop. A common third stage uses a clean dry mop or a hand cloth charged with a clean rouge or with no compound at all. Lapidary finishing, on a faceting machine, runs through pre-polish on a fine ceramic or copper-tin lap, then a polishing lap charged with the species-appropriate compound, with each stage requiring its own dedicated lap to avoid contamination of finer abrasives by coarser residues.
In the trade
Polishing compounds are consumables and are matched to the work at hand. A bench jeweller with five customer rings on the board may switch between three or four compounds in a single session. Substituting a coarser compound at the final stage will not save time — it will leave a fine network of scratches that the customer will see, and the work will have to be cut down and refinished. The discipline of compound sequencing, more than any other skill, distinguishes a polishing operator who can produce a saleable finish from one who cannot.