Teated synthetic moissanite by coating 

The French gemmological laboratory (Laboratoire Français de Gemmologie – LFG) has recently received a 0.41 carat pink stone for identification. The first observations brought up doubts about the natural origin of its colour. The surface of the stone contains numerous patches (photos 1 and 2)

Photo 2: metallic punctuations on the surface of the studied stone (field of view: 1.8 mm approx., by A. Delaunay)

Photo 3: doubling of the edges observed by the crown in this synthetic moissanite (field of view: 3.4 mm approx., by A. Delaunay)

Under microscope, these punctuations have metallic reflects, sometimes along oxidation parts. Furthermore, the pink colour seems concentrated at the surface. Some unevenness in the colour can be observed due to scratches of this film. When the gem is observed through the crown, the gem shows a clear doubling of its edges indicating that the material is anisotropic. These elements clear up the client’s doubt of the gem being a pink diamond (photo 3).

The stone has been analysed with several scientific instruments such as infrared, UV-Visible and Raman spectrometers. All the spectra collected indicate that it is a synthetic moissanite treated by coating with coloured film. The chemical study of this film revealed elements responsible for the colour of the calcium rich film: iron and titanium.

This is the first example of synthetic moissanite treated by coating with a thin coloured film identified at the LFG. This type of treatment is not rare on topaz, quartz, or even diamond or tanzanite. Therefore, gemmologists must remain vigilant because this treatment can be done to all gems natural or synthetic.