Alizarin red S is sometimes used to demonstrate calcium in sections. Unlike the more commonly used method for calcium, the von Kossa, it combines with the calcium ions forming a bright red lake. It is commonly used to stain embryo skeletons in cleared whole mounts, usually of small mammals. Although sometimes simply called alizarin, it should be noted that another dye, from which it is derived by sulphonation, is more properly called by that name.