When sourcing recycled glass, the primary quality metric is purity and the absence of contaminants. You must ensure the supplier provides color-sorted cullet (flint, amber, or green) to prevent batch discoloration in manufacturing. Key technical specs include particle size distribution (mesh size), which affects melting efficiency, and a contamination limit of <50 grams per ton for non-glass materials like ceramics, stones, and porcelain (CSP). Always request a chemical composition analysis to verify the absence of heavy metals like lead or cadmium, especially for food-grade packaging applications.