Abrasion (6.34)
The most probable cause of abraded facets is the cutter’s error in polishing off-grain, or failing to keep the scaife properly charged with the oil-and-diamond-powder mixture. As discussed previously, the cutter must polish each facet on the diamond perpendicular to the dominant individual grain that runs through the area being cut. As with a carpenter’s crosscut saw, it is much more effective to saw perpendicular to the grain, making it easier and faster. In diamond, the same principle applies. By cutting off-grain, the facet cuts much more slowly, leaving obvious polishing lines and abraded facet edges and surfaces. Sometimes, especially on the pavilion (bottom) of the stone, the cutter may allow his cutting wheel to get too dry, which can cause graying (slight abrading). The off-white or grayish cast can be very apparent or it can be so faint that it takes time to locate.
The storage of diamonds together in a paper parcel can also cause abrasions and/or scratches on a diamond’s surfaces. This is usually the case with lower quality stones or smaller stones, since the value woud not be affected as dramatically as it would with larger, more valuable stones.
Diamonds can also be abraded through everyday wear. Tiny nicks show up on the crown of a mounted diamond after many years of abrupt contact against hard surfaces. Again, since diamond is so hard, it does have a slight tendency to be brittle. Usually abrasions can be removed with very little weight loss. The facets are re-polished, producing those sharp, clean edges that only occur in diamond.
