Polish lines are fine parallel grooves and ridges left by polishing. They can occur on any facet but don't cross facet junctions, and they look transparent or white.
In more detail
A diamond's cutter works each facet in its own direction, because diamond is harder in some directions than in others. Polish lines that run the same way on facet after facet are a clue to moissanite, not proof.
On a grading report
A blemish; polish lines count in the polish grade and can stop a stone from being Flawless.
Related terms
- Polish: Polish is the grade for the smoothness of the facet surfaces, from Excellent to Poor. The grader looks at 10x for pits, nicks, polish lines, scratches, burn marks and rough patches.
- Flawless (FL): Flawless (FL) is the top clarity grade: a skilled grader finds no inclusions and no blemishes at 10x magnification.
- Burn mark: A burn mark is a hazy area on a facet surface, caused by too much heat during polishing. It is also called a burned facet.
- Facet doubling: Facet doubling is the double image of facet edges seen through a strongly doubly refractive stone. It shows clearly in moissanite under a 10× loupe.
- Blemish: A blemish is a clarity characteristic confined to the surface of a diamond.