Eriochrome Blue Black R is widely used as a metallochromic indicator in complexometric titrations, particularly for determining metal ions such as calcium, magnesium, and zinc. It forms colored complexes with these metals, allowing for precise endpoint detection in titration processes. In water hardness testing, it is employed to measure the concentration of calcium and magnesium ions, providing critical data for water quality assessment. Additionally, it is utilized in dyeing textiles, where it acts as a mordant dye, forming stable complexes with metal ions to enhance color fastness on fabrics. Its ability to interact with metals also makes it useful in analytical chemistry for metal ion detection and quantification.