Function

An inclusion plot, sometimes called a clarity plot or simply a plot, is a schematic diagram of a gemstone showing the location and approximate appearance of internal inclusions and external blemishes. It appears on most diamond grading reports issued by the GIA, AGS, IGI, HRD and similar laboratories, and on some coloured-stone reports. The plot enables an examiner to verify the identity of a stone by comparing the plotted inclusions against the actual stone under magnification.

Construction

The plot is conventionally drawn from two views: the crown view (looking at the stone face-up) and the pavilion view (looking at the stone face-down). For round brilliant diamonds, both views show the eight-fold symmetry of the standard cut. For fancy shapes, the views reflect the specific cut. Inclusions are marked at their actual locations using standardised symbols and colours. Internal inclusions are typically marked in red; external blemishes are marked in green. The symbol shape conveys the inclusion type: a small circle for a crystal, a line for a feather, a dot for a pinpoint, and so on.

Use

The plot serves three functions. First, it documents the clarity assessment, showing why the stone received its grade. Second, it provides a unique fingerprint for the specific stone, since the inclusion pattern is unique and reproducible across examinations. Third, it allows independent verification by a third-party examiner who can compare the plot against the stone's actual inclusions.

For the working trade, the plot is the principal evidence that a graded stone matches its certificate. A buyer receiving a stone with its certificate should verify the plot under magnification before accepting delivery. Mismatches between plot and stone, whether by error or by substitution, are detected this way.

Limitations

Inclusion plots are not exhaustive. The plot shows the inclusions that determined the clarity grade, not necessarily every visible feature. Very small pinpoints, surface graining and other features that did not affect the grade may not be plotted. The plot is also schematic rather than photographic; the actual visual appearance under magnification may differ in detail from the plot's representation.

For coloured stones, plot precision varies more than for diamonds. Coloured stone reports from major laboratories generally include plots only for higher-value stones or on request, and the inclusion patterns can be complex enough that a schematic plot conveys less information than a clarity description in text.