Sudan IV is a lysochrome (fat soluble dye) predominantly used for demonstrating triglycerides in frozen sections, but which may also stain some protein bound lipids in paraffin sections. It is less popular than oil red O as it has a more orange shade.
Gurr notes that a purified form of this dye has the name "Biebrich scarlet R". It should not be confused with the water soluble dye which is much more commonly referred to as Biebrich scarlet. This latter dye is not a lysochrome, but is used as a plasma stain in trichrome techniques.
R. D. Lillie.
Conn's Biological Stains
Williams & Wilkins, Baltimore, MD., U.S.A.
Edward Gurr, (1971)
Synthetic dyes in biology, medicine and chemistry
Academic Press, London, England.
Aldrich chemical catalogue, 1992
Aldrich Chemical Company, Milwaukee, WI, USA.