A quality diamond necklace should include GIA or AGS certification for significant stones, documenting color, clarity, cut precision, and confirming natural origin. For vintage pieces, authentication certificates from recognized appraisers establish provenance and confirm period-appropriate craftsmanship techniques. Conflict-free verification documentation increasingly accompanies luxury diamond pieces, confirming ethical sourcing practices throughout the supply chain. Additionally, designer diamond necklaces should include brand certificates of authenticity, particularly for bespoke or limited-edition creations that represent significant investment value.