Fuchsin acid calcium salt is primarily used in biological staining techniques, particularly in histology and microbiology. It is a key component in various staining protocols, such as the Gram stain, where it helps differentiate bacterial species based on cell wall properties. The compound is also employed in the Ziehl-Neelsen stain for identifying acid-fast bacteria like Mycobacterium tuberculosis. Additionally, it is utilized in textile dyeing processes, where it imparts vibrant colors to fabrics. Its application extends to the preparation of certain inks and as a pH indicator in laboratory settings. The compound's staining properties make it valuable in research and diagnostic laboratories for visualizing cellular structures and microorganisms.