Eriochrome Blue Black R also known as Calcon Mordant Black 17. It is an azo dye that is commonly used as a metal indicator in complexometric titrations, particularly for determining the presence of aluminum, iron, and zirconium. It’s an organic compound primarily used as a complexometric indicator for the determination of metals like aluminum, iron, and zirconium. It’s also used as a dye, particularly in textiles and leather, and requires a mordant to fix the dye onto the material.