Von Kossa stain is widely used in histology to detect the presence of abnormal calcium deposits in the body. The principle of this coloration is based on the transformation of calcium salts into silver salts: calcium ions, bound to phosphates, are replaced by silver ions brought by a solution of silver nitrate. Placed under a light source, the silver phosphates undergo a photochemical degradation, leading to the observation of metallic silver deposits. Counterstaining with nuclear red allows to stain the nuclei of the cells in red and their cytoplasm in pink.

This stain is useful for the diagnosis of calcinosis (eg chondrocalcinosis, nephrocalcinosis, cutaneous calcinosis ...). It can also be used to detect calcifications in tumors.

Von Kossa stain can be used on all types of tissue that may have abnormal calcium deposits. The joints, blood vessels and kidneys are most often affected.