Property Data
Common name
Suggested name
Other names
C.I. number
C.I. name
Solubility aqueous
Solubility ethanol
Absorption maximum
Empirical formula
Formula weight

None (1st ed. 1242)
Natural red 28
579 (Aldrich)
Reddish brown

Orcein was originally obtained from lichens, but is now made from orcinol by hydrogen peroxide oxidation with ammonia present. It is a standard dye to use for the demonstration of elastic fibres, when it is applied in an acid, alcoholic solution. This same solution has also been shown to stain the rough endoplasmic reticulum of hepatitis B infected liver cells (ground glass cells).


Compound R1 R2 R3 %
α-Aminoorcein H O NH2 10
α-Hydroxyorcein H O OH 10
β-Aminoorcein Orcinol O NH2 6
γ-Aminoorcein Orcinol O NH2 12
β-Hydroxyorcein Orcinol O OH 15
γ-Hydroxyorcein Orcinol O OH 10
β-Aminoorceimine Orcinol NH NH2 1-2
γ-Aminoorceimine Orcinol NH NH2 1-2

Orcein is a variable mixture of several compounds. These compounds differ at the points marked R1, R2 and R3 in the structural formula. The chart to the left gives the commonest eight of these compounds, with the groups at each of the three points. The % column is the approximate percentage of each compound in synthetic orcein.

Compare the formulas of these eight compounds.


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

Aldrich chemical catalogue, 1992
Aldrich Chemical Company, Milwaukee, WI, USA.

Susan Budavari, Editor, (1996)
The Merck Index, Ed. 12
Merck & Co., Inc., Whitehouse Station, NJ, USA

Musso H, (1960)
Orcein and litmus pigments: constitutional elucidation and constitutional proof by synthesis.
Planta Medica, v. 8, p. 431-446




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