Overblue

Refers to a diamond that glows (fluoresces) strong blue under long wave ultraviolet light; in the past the term was used misleadingly to imply a diamond with superior colour. In fact, some diamonds with a high colour grade that have very strong fluorescence can look oily or milky under daylight.

Nick

Type of diamond blemish that that appears as a tiny break out of the edge of a diamond, not large enough to be a called a chip and usually confined to the girdle. Nicks affect the polish grade of a diamond.

Needle

Type of diamond crystal inclusion where a mineral deposit, or sometimes another diamond, is trapped inside the diamond. Needles look like elongated bubbles of various shapes and sizes.