Cellini has its own gem testing facility on the premises and a gemologist is on hand six days a week to assess and identify any type of gemstone. There may be a charge for this service.

Synthetic gemstones were first created in the late nineteenth century and have proliferated since, created by ever more sophisticated processes. The most commonly synthesized gemstones are ruby, sapphire, and alexandrite. The number of laboratory grown, synthetic gemstones have become widely used during the last decade, with stones such as "Synthetic Moissanite", having been developed as a difficult to detect diamond substitute.

Additionally, unregulated manipulation and treatments of natural gemstones has now become common place. Also the laser treatment and subsequent re-filling of fractures in diamonds, and other gemstones, with glass is widespread, particularly in the Far East and USA. Other problems include natural sapphire colours being altered by surface treatments, and natural jade being dyed to enhance the colour.

Cellini uses its gem testing facilities as part of the in-house valuation service, as well as providing an examination, identification, and verification service.