A natural is the original surface or skin of a rough diamond. Naturals can be located anywhere on a polished diamond, but for the most part, they are on or around the girdle. The size of a natural determines whether it is either a blemish or an acceptable characteristic.
When a cutter is not concerned with clarity, it is likely that a large natural (or naturals) will be left on the crown or pavilion. On imperfect diamonds, large naturals will not affect clarity; hence weight retention is the highest priority. (The more the stone weighs, the more valuable it will be.)
The ideal natural will be enclosed in the girdle, not protruding into the crown or pavilion. A natural protruding into the crown is more negative than into the pavilion, because, upon looking down on the stone, a natural that just breaks into the pavilion will probably not be detected. Obviously when the natural strays into the crown, it is more easily seen and taken into account in clarity grading.
On higher clarity stones, the cutter must be very aware of how large the natural will appear after completing the polishing process. The goal of the cutter should be to locate two opposite naturals of the same size, leaving them small enough to be hidden when viewed from the crown. This also means that the naturals must not interrupt the outline shape of the stone.
Naturals are an excellent reference for identifying authenticity in diamonds. Some naturals can look almost like a polished facet, whereas others are rough and can be mistaken for a chip. Indented naturals look like cavities; again these would fall into the inclusion category since they occur below the surface. Trigons are triangular-shaped impressions on the natural that also indicate grain orientation to the cutter. Naturals have a very distinct appearance unlike chips and facets, so it is important to familiarize yourself with this common characteristic. On the diamonds that you have available to look at, focus on the girdle area and when you’ve located the first natural, turn the stone 180° to see if the cutter did a good job in obtaining maximum weight retention. Of course, many times the opposite natural will not occur due to other issues, such as inclusion removal.