A reflectance spectroscopy study of one commercially available dye based on carminic acid found that it reflects mostly red light with wavelengths longer than about 603 nm,[7] which provides its saturated red color.
Carmine can be used as a staining agent in histology, as a Best's carmine to stain glycogen, mucicarmine to stain acidic mucopolysaccharides, and carmalum to stain cell nuclei. In these applications, it is applied together with a mordant, usually an Al(III) salt.
Carmine was used in dyeing textiles and in painting since antiquity.[8] It is not very stable in oil paint, and its use ceased after new and better red pigments became available. Jacopo Tintoretto used carmine in several of his paintings, including Portrait of Vincenzo Morosini[9] and Christ Washing the Feet of the Disciples.[10]