gems, corundum, color.4, treatments.6, irradiation, irradiation paper on ruby, yellow sapphire

Yellow sapphire is one of the most obvious color instability reported. Color instability of gemstones refers to the phenomenon that gemstones are exposed to ultraviolet or sunlight to produce color changes visible to the naked eye. The color instability of gemstones has attracted attention as early as 1981. Schiffmann[1] reported that a yellow sapphire from Sri Lanka faded significantly to light yellow after 36 hours of irradiation under 365 nm ultraviolet light. In recent years, Cara Williams et al. [2] reported in 2016 that the color of a yellow sapphire of unknown origin changed from yellow to colorless after being heated at low temperature, and returned to yellow when exposed to long-wave ultraviolet or sunlight for a period of time. In 2018, Michael S Krzemnicki et al. [3] found that this color instability also appeared in the color Papalacha sapphire. This phenomenon of color instability greatly affects the commercial value of gemstones and is not conducive to market stability. How to effectively identify this color unstable gemstone and what will lead to the emergence of gemstone color instability is an important topic in current gemology research.