A method for evaluation of a gemstone

An apparatus for determining location of at least one inclusion in a gemstone having a first refractive index, comprising: a container adapted for containing a material having a second refractive index, a holder operative to support a gemstone in the material when the container contains the material; an illuminator positioned and adapted to illuminate said gemstone when disposed within said material in said container, with illumination at which said gemstone and said material have their respective first and second indices; a detector that detects illumination from the illuminated gemstone and said material and produces signals responsive thereto; a controller that receives the signals and is operative to determine a location of an inclusion in the gemstone based on the signals; and a system, operative to reduce the presence within said material, at least when the gemstone is disposed therein, of any substance other than inclusions, having a third refractive index.