The durability of Akoya pearls is closely related to the mechanical strength of the nacre. Therefore, obtaining information about the mechanical strength of the nacre is very important in the quality control of pearls. The nacre of Akoya pearls is composed of aragonite contained within an organic matrix. The presence of the organic matrix provides mechanical strength and fracture toughness much higher than that of monolithic aragonite. In this study, we investigated the hardness and delamination strength of Akoya cultured pearls classified into four levels by "Gray Value (GV)", a score given by a non-destructive inspection method based on UV fluorescence intensity that provides an indication of the condition of the nacre's organic components. Pearl hardness decreased significantly with decreasing GV. Furthermore, delamination strength of the pearl surface layer was very low when the GV was very low. These results suggest that the GV indirectly represents the mechanical strength of the nacre and could be used as a non-destructive quality-control method to maintain the quality of pearls used as jewelry.
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