Introduction Turquoise, best known for its splendid blue colour, has been used for adornment since antiquity. Chemically a hydrous copper aluminium phosphate, it has a cryptocrystalline structure composed of fine, randomly oriented groups of triclinic crystals (Webster, 1994). This cryptocrystalline structure gives rise to the gem’s porosity, making it susceptible to body oils, ordinary solvents, or even dirt, which can alter its colour. For decades, turquoise has been impregnated with wax, plastics, or polymers—a process known as stabilization, which enhances not only the material’s durability but also its colour and surface lustre (Nassau, 1994). Another established treatment is the dyeing of pale-coloured turquoise to give it a rich blue colour (see, e.g., Kammerling, 1994). In recent years, a few other proprietary treatments have been developed for turquoise. The most prominent is Zachery treatment, which decreases the porosity of the original material, so it takes a better polish; the blue colour may also be enhanced through an additional step in the process (Fritsch et al., 1999). Another form of treatment seen on the market, developed by Eljen Stones, involves polymer impregnation (Owens and Eaton-Magana, 2009).