Division of Radiooncology, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany
Before the era of haematoxylin and synthesized aniline dyes as histological stains, the method of choice to stain tissue sections was one of the natural dyes such as carmine. Carmine is obtained from the bodies (female) of the insect Dactylopius coccus cacti. The active coloring agent in carmine is carminic acid (C.I. 75470, Natural red 4). For nuclear staining it is invariably used in conjunction with a mordant such as alum solution. Carmine staining can be an alternative to haematoxylin counterstaining of immunostained tissue sections. A variety of carmine formulations exist for very clean and sharp nuclear staining. The most popular formulations are given here.