When sourcing aluminium scrap, quality is determined by the purity levels and the presence of contaminants. Buyers should categorize scrap based on ISRI (Institute of Scrap Recycling Industries) codes, such as 'Tense' (mixed cast), 'Taint/Tabor' (clean sheet), or '6063 Extrusions'. It is critical to verify the chemical composition using XRF (X-ray fluorescence) analyzers to ensure the silicon, iron, and copper content meets your smelting or manufacturing specifications. High-quality scrap should have minimal attachments (plastic, rubber, or steel) and be free of excessive oxidation or moisture, which can lead to significant melt loss.