Ammonium oxalate is widely used in analytical chemistry as a reagent for the determination of calcium ions in various samples. It forms a precipitate with calcium, allowing for accurate quantification in water, biological fluids, and other materials. In histology, it serves as a decalcifying agent to soften hard tissues like bone, making them easier to section for microscopic examination. Additionally, it is employed in the textile industry as a mordant to fix dyes onto fabrics, ensuring colorfastness. In photography, it acts as a component in certain developers and toners to enhance image quality. It also finds use in metal cleaning and polishing processes, particularly for removing rust and stains from metal surfaces.