When sourcing crystal beads, the primary distinction lies between K9 optical glass (lead-free) and lead crystal (containing 24% to 30% lead oxide). Lead crystal offers a higher refractive index and superior brilliance, while K9 glass is more cost-effective and eco-friendly. You should request high-resolution photos or videos under natural light and spotlight to check for internal bubbles, scratches, or cloudiness. High-quality beads should have sharp, precise facets that maximize light dispersion.