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Sirius Red F3B

Sirius Red F3B

Class: Azo
Ionisation: Acid

Chemical structure of Sirius Red F3B

Common Name: Sirius red F3B
Suggested Name: Sirius red F3B
Other Names:

C.I. Number: 35780
C.I. Name: Direct red 80
Color: Red
Solubility Aqueous: Moderate
Solubility Ethanol: Moderate
Absorption Maximum:
Empirical Formula: C45H26N10O21S6Na6
Formula Weight: 1373.1


Sirius red F3B has been recommended as a substitute for acid fuchsin in van Gieson type procedures. It is also used for the demonstration of amyloid in techniques similar to those using congo red, depending on hydrogen bonding and formation of a "pseudocrystal." Like congo red it shows green birefringence, but it is a little darker.

Do not confuse this dye with sirius red 4B, which is not used for the demonstration of amyloid.

Compare this dye to other direct cotton dyes for amyloid.


  1. R. D. Lillie.
    Conn’s Biological Stains
    Williams & Wilkins, Baltimore, MD., U.S.A.