No diamond can be referred to be really clean. In all diamonds inclusions or in general internal characteristics will occur. These are crystalline inclusions, fractures, cleavages (feathers) and some kinds of structure phenomena. In addition there are the external characteristics like naturals and extra facets, polishing faults and bearding. These characteristics belong to the essential character of the precious stone. In particular, the definition generally accepted in the diamond business assumes that:

A diamond is called “loupe-clean” if, after an examination by an experienced grader with a loupe 10x (corrected for spherical and chromatic aberration), it has been found free of internal characteristics. It is recommended that the characteristics of the artificial light source used, approximate the C.I.E.-standard illuminant D65.