Surface Graining (6.43)
Surface graining, like internal graining, is an irregularity of the crystal structure of the diamond. It appears as a line traveling across one or more facets. Grain lines are more obvious than polishing lines, although they can be mistaken as polishing lines, especially when occurring in a multiple pattern. Polishing lines will be in larger numbers running tightly together. A single grain line can run across several facets continuously, whereas polishing lines will at least change direction slightly from one facet to the next.
Removing a grain line from the surface is largely a futile attempt at improving clarity. Since the line itself is part of the diamond crystal, it will generally run deep into the stone even though, under magnification, it is not apparent below the surface.