Buyers must prioritize particle size distribution (PSD), as it determines the visual effect: 10-60μm provides a classic pearlescent luster, while smaller sizes (<15μm) offer a silky matte finish and larger sizes (>100μm) create a sparkling, glitter-like effect. Additionally, verify the substrate material, typically natural mica, synthetic mica (fluorphlogopite), or glass (borosilicate). Synthetic mica is preferred for high-end applications due to its superior whiteness, higher transparency, and lack of impurities compared to natural mica.