The last lap is the final polishing lap mounted on a faceting machine, used to bring each facet to its finished, smear-free polish after rough cutting and pre-polishing have established the geometry. Choice of lap material and polishing agent at this stage determines the surface quality of the finished stone, and a well-chosen last lap is the difference between a stone that reads "commercial" under a loupe and one that reads "fine".

Common last-lap combinations vary by species. Tin or composite tin-alloy laps charged with diamond paste at 0.25 to 1 micron are the default for corundum, beryl and chrysoberyl. Solid copper or composite laps charged with cerium oxide or alumina are typical for quartz, tourmaline and garnet. For diamond itself, the last lap is invariably a cast-iron scaife, charged with diamond grit of decreasing micron size as the cut progresses. Wax laps and ceramic laps are used for soft species such as fluorite, where harder laps would tear out facet edges.

Operationally, the lap is run at a moderate speed, the stone is held against it with light pressure on the dop, and each facet is polished only as long as needed to clear the pre-polish lines. Overworking a facet on the last lap rounds the edges, softens the meet points, and degrades the overall make. The mark of a well-executed last lap is sharp meet points, crisp facet edges, and a polish so clean that it returns no orange-peel texture under 10x.