Abstract: A method of determining the composition of a polished gemstone comprises passing an excitation beam through the gemstone from a table facet substantially to a culet of the gemstone, an axis of the excitation beam being substantially perpendicular to the table facet; and capturing luminescence emitted by the gemstone from an angle oblique to the axis of the excitation beam.

Abstract: A method of characterising a composition of a gemstone comprises irradiating an upper portion and a lower portion of the gemstone with one or more pulses of ultraviolet radiation at a wavelength of substantially 225 nm or less; capturing luminescence emitted by the upper portion of the gemstone and luminescence emitted by the lower portion of the gemstone in one or more time windows having a predetermined relationship with the or each pulse; and comparing properties of the captured luminescence from the upper and lower portions. A composition of the gemstone is characterised, based upon the comparison.