Sometimes by reason of weight retention, the cutter is forced to leave an indented natural. Naturals are very common on diamonds since they are a cutter's guideline for getting the maximum potential weight out of a piece of rough. By leaving opposite naturals, the cutter knows the maximum possible diameter of the stone has been achieved. Such naturals lie across the narrowest diameter of the original rough. When they form small canyons or indentations, the cutter may choose to leave these characteristics instead of losing additional weight by removing them.
An indented natural is more serious than a level natural since, like a cavity, it has a tendency to collect dirt and oil, acquiring a dark appearance. This can easily be cleaned up, leaving no traces of dirt. Cavities can be more fragile, whereas naturals, indented or not, are much more rugged, having already survived nature's punishments during the past ages.
The ideal natural is one that does not take away the roundness or symmetry of the diamond and cannot be detected looking downward on the crown. It will be fully enclosed in the girdle, or there will be at least a small amount of girdle between the crown and the natural. Some naturals are left creeping slightly into the crown or pavilion under magnification, these can be just detectable when viewed through the crown. Naturals that are left just traveling into the pavilion are more easily hidden than crown naturals. An indented natural is considered an inclusion since it does extend below the surface of the finished stone.