• A diamond coating may contain minute particles of some foreign material, striaes, and air bubbles, which are usually located at the interface between the diamond and the coating, but can be sometimes found in the coating material itself.
• The coating material may be unevenly colored, which is revealed by carefully examining the diamond. When viewing the stone "from the side", one may notice that the colors of the pavilion and crown differ in saturation.
• There may be mechanical defects, such as scratches and worn areas, on the coating material. This feature is easiest to notice when illuminating the diamond with a fiber-optic light source.
• The luster of the coating material may be slightly nonuniform. This feature is easiest to notice when illuminating the diamond with a fiber-optic light source: some portions of the coated surface look turbid.

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- Carefully clean the sample under study before starting the diagnostics.
- Examine the sample under a gemological binocular microscope. Attentively search for features of diamonds treated by coating.
- When looking for the diagnostic features of diamond coating, focus your attention on the surface of the studied sample. For this purpose, alternate between "dark field" illumination and direct light emitted by the fiber-optic light source, which is reflected by diamond facets.