[Valeria101]

Looks like an intricate version of 'candling':


Method and apparatus for the positive identification of a natural pearl and for measuring the thickness of the nacre coating of cultured pearls.

Inventors: Russell; Kenneth M. (Bethesda, MD)
Appl. No.: 07/941,175
Filed: September 4, 1992


Abstract
An apparatus comprising a light source, a lens system, a reticle illuminated by the light source, a housing having a substantially dark viewing chamber and a pearl holder for holding the cultured pearl in the substantially dark viewing chamber, and a reticle device for providing a reticle image observable through the lens system. The substantially dark viewing chamber is optically connected to the light source so as to allow light from the light source to traverse an aperture in the pearl holder to illuminate the pearl. The substantially dark viewing chamber is also optically connected to the lens system. In order to provide maximum contrast between light and darkness in the substantially dark viewing chamber, the housing is arranged to prevent entry of extraneous light into the substantially dark viewing chamber. A preferred method according to the present invention includes the following steps. A pearl is placed in the substantially dark viewing chamber. The pearl is illuminated by irradiating a relatively small portion of a side of the pearl with light from the light source, so that luminescence is stimulated throughout the pearl only when the pearl is a natural pearl, and so that the thickness of the nacre coating is observable through the lens system when the pearl is a cultured pearl. The thickness of the nacre coating of the illuminated pearl is measured by comparison with the reticle image observed through the lens system.