The face of a plank may contain unlimited sound sapwood. Color variation is prominent. Small burls, light brown streaks, restored knots up to 25 mm, properly filled open checks and worm holes, slight imperfections in face work (torn grain) and burns are admitted. When stained in a dark color, surface appears uniform in shade and texture, making knots etc barely discernible. 1 Natur grade is used to classify wide plank flooring 190 mm.