In diamond grading, a knot is a transparent or translucent diamond crystal inclusion that reaches the polished surface of a finished stone, typically appearing on the table or on a crown or pavilion facet as a slightly raised or differently oriented patch of diamond material. Knots are one of the standard inclusion types recognised in the GIA grading nomenclature and are reported on the inclusion plot of a GIA Diamond Grading Report when present.

Identification

A knot is distinguished from other surface-reaching diamond inclusions by its character as an embedded crystal of diamond rather than a fracture or feather. Under loupe inspection at ten power, a knot appears as an outlined area within a facet, often with a faint boundary line where the crystal inclusion meets the host crystal, and sometimes with a slight difference in surface polish where the two crystals took the polishing lap at slightly different rates. In tilt views, a knot can show subtle differences in transparency or, more rarely, a faint cloudy or coloured appearance.

Effect on grading and durability

A knot is a clarity feature reportable on the inclusion plot. Its effect on the clarity grade depends on size, position and visibility under ten-power magnification, in the same way as any other inclusion. The principal additional concern with knots, beyond their clarity impact, is durability and finish. Because the inclusion is itself diamond, polishing forces during recutting can cause the knot to chip out of the host facet, leaving a polish defect that requires further work. Setters should avoid heavy pressure on facets containing knots when bezel-setting or pressure-fitting, since the boundary between the host and the knot can be a stress riser under mechanical load.