Pigments through the Ages - Technical Information

About the chemical structure:

Chemical name:	complex aluminosilicate minerals
Formula:	K[(Al,Fe^III),(Fe^II,Mg](AlSi₃,Si₄)O₁₀(OH)₂
Crystal system:	Monoclinic - Prismatic (at Mineralogy Database)
Refractive index:	alpha =1.59-1.612, beta =1.609-1.643, gamma =1.61-1.644

Color:

Color Index (C.I.)

PG 23

How can you identify Green earth?

Imaging:

UVF: no

FCIR: pink

Perugino, Chapel of Saint Severo, 1520, Perugia, Italy

Restoration of the green gown of the right side saint was made in green earth, indeed the green pigment shows up pink in IRFC. The original green pigment is malachite which is blue in the IRFC.

OM: it can often appear as a confusing mixture of particles. Crystals are course and rounded. Most appear a grayish-green but many characteristic translucent, angular silica particles are usually apparent. Some distinctive yellow or brown crystals may also be seen.
Polycrystalline aggregates, particles are usually 1-30μm in size.

Microscopic appearance at x500 mag

Analytics:

It's identified by means of FTIR and Raman. Confirm with microchemical tests for ferric and ferrous iron as long as the ions are put into solution by the treatment with acid.The organic base reacts ferrous salts in acid solutions to give a stable, deep red cation.

Raman spectra: University College London;

FTIR spectra: IRUG;

Usage and handling:

Permanence:	Toxicity:
lightfast: excellent Degradation processes: no one. Earth pigments, and green earths in particular, are often described as the most permanent of colors. Earths are not affected by sunlight or by atmospheric conditions. They do not react with solvents, but according to Feller, green earth is partially soluble in acids and alkalis.	non toxic. The pigment is considered non-toxic, but care should always be exercised when handling the dry powder pigment so as not to inhale the dust. MSDS: Kremer

Permanence:

Toxicity:

lightfast: excellent

Degradation processes: no one. Earth pigments, and green earths in particular, are often described as the most permanent of colors. Earths are not affected by sunlight or by atmospheric conditions. They do not react with solvents, but according to Feller, green earth is partially soluble in acids and alkalis.

non toxic. The pigment is considered non-toxic, but care should always be exercised when handling the dry powder pigment so as not to inhale the dust.

MSDS: Kremer