About the chemical structure:
| Chemical name: | Iron(III)-oxide, partly hydrated + manganese oxide + aluminium oxide |
| Formula: | Fe2O3 (· H2O) + MnO2·(n H2O)+ Al2O3 |
| Refractive index: | n/a |
Color:
| Color Index (C.I.) | PBr 8 (Raw umber): PBr 7 (Burnt umber) |
How can you identify Umber?
Imaging:
UVF: no
IRFC: dark yellow
OM: generally particles are heterogeneous and characteristically rounded. Burnt umber particles are almost identical to that of the raw umbers. Burnt umber particles, however, do tend to be redder and sometimes appear more transparent. Particles size of all umbers is usually between 1-50μm.
Microscopic appearance at x500 mag
Analytics:
It's identified by means of FTIR and Raman.
Raman spectra: University College London;
FTIR spectra: IRUG
Usage and handling:
| Permanence: | Toxicity: |
|---|---|
Lightfast: excellent Degradation processes: grades and therefore permanence varies and poor grades, which contain humus matter are fugitive. Generally, however, all umbers are considered to have excellent permanence. All umbers are unaffected by alkalis and dilute acids. All have high oil absorption requiring around 18% oil to grind them in oil paints. As a result the latter oil films tend darken with age. |
non toxic. MSDS: Kremer |
Literature:
Fuller. Carl, Natural. Colored Iron Oxide Pigments pp. 281-6. Pigment Handbook, 2nd Edition. Lewis, P. (ed.). New York: John Wiley & Sons,1988.
Thomas, Anne Wall. Colors From the Earth, New York: Van Nostrand Reinhold, 1980.
Sections: