Calcium is the most abundant mineral in the human body, and is the main component of bones and teeth. Under normal conditions, calcium should not form calcium salt in other tissues except bones or teeth. However, under pathological conditions, calcium forms carbonate or phosphate and is deposited in tissues.

2% Alizarin Red S Staining Solution, pH4.2 is widely used for staining calcium deposits for decades. Alizarin Red S can chelate with calcium salts to form a purple-red or orange-red complex. This staining solution is acidic, which is very suitable for staining extracellular matrix calcium deposition such as bone and cartilage.