When sourcing master alloys, the chemical composition accuracy is paramount. You must verify the percentage of alloying elements (e.g., AlTi5B1, AlSr10, AlMn10) and ensure impurity levels (like Fe, Si, or Ca) are within the strict tolerances required for your final melt. Additionally, consider the physical form (waffle ingot, coil, or rod) to ensure compatibility with your furnace feeding systems. High-quality alloys should feature a fine and uniform microstructure to ensure rapid dissolution and consistent grain refinement.