Indigo

About the chemical structure:

Chemical name:	Indigotin (2,2'-Biindolinyliden-3,3'-dion)
Formula:	C16H10 N2O2
3D model:	grey = carbon, red = oxygen, white = hydrogen, blue = nitrogen
Crystal system:	rhombic
Refractive index:	n/a

Color:

Color Index (C.I.)

NB 1

How can you identify Indigo?

Imaging:

UVF: no

FCIR: red

Maestro della Maddalena, XIII century, Italy

Left, visible image. Middle, IRFC image. Right, restoration mapping: blue, original XIII century, red XVIII restoration, blue XIX restoration.

The blue bonnet of the Virgin shows up in red (left side) and black (right side) in the IRFC. Indeed, the left was restored with indago in the XVIII century, while the right side was repainted in prussian blue.

OM: Deep blue, regular and slightly rounded particles. All particles are very fine. Some deep blue needle shaped particles often seen.
Particles are difficult to analyze and almost no distinct particles can be seen at magnification. Particles are usually between 1-10μm in size.

Microscopic appearance at x500 mag

Analytics:

It's identified by means of FTIR and Raman.

Raman spectra: ColoRaman

FTIR spectra: IRUG

 

Usage and handling:

Permanence:	Toxicity:
Lighfast: poor. Degradation processes: it has high tinting strength but may fade rapidly when exposed to strong sunlight. It is best used full strength and protected from ultraviolet light beneath a UV-protecting varnish or glass.	non toxic. MSDS: Kremer

Literature:

Seefelder, M., Indigo - Kultur, Wissenschaft und Technik, Ecomed Verlag, Landsberg 1994

Artists’ Pigments. A Handbook of Their History and Characteristics, Vol. 3: E.W. Fitzhugh (Ed.) Oxford University Press 1997, p.81-107.

Indigo (at Pigmentlexikon by Th. Seilnacht)