Pigments

Today, there are hundreds of different inorganic pigments known, which can be distinguished by colour and chemical composition. Let’s look at some of the important inorganic pigments, both natural and synthetic:

• WHITE – Earth pigments: kaolinite, chalk (CaCO₃), diatomite (SiO₂); synthetic: lead white (2PbCO₃·Pb(OH)₂), barium white, BaSO₄, titanium white, TiO₂ 
• YELLOW – Earth pigments: yellow ochre and yellow umber (clay, limonite, goethite); orpiment (As₂S₃); synthetic: lead chromate (PbCrO₄xPbSO₄), lead-tin yellow (Pb₂SnO₄, PbSn₂SiO₇), zinc yellow (Zn₂CrO₄), Naples yellow (Pb(SbO₃)₂) 
• RED – Earth pigments: red ochre (α-Fe₂O₃), terra di Siena (α-Fe₂O₃), bauxite, terra rossa; hematite (Fe₂O₃), cinnabar (HgS), realgar (AsS); synthetic: vermilion (HgS), lead red (Pb₃O₄), chrome red (PbCrO₄xPbO) 
• GREEN – Earth pigments: green earth (terra verde, Fe-silicates), terra viridis (Cu-silicates); malachite (CuCO₃·Cu(OH)₂); synthetic: Paris green (Schweinfurt green, C₄H₆As₆Cu₄O₁₆), verdigris (Cu-acetate) 
• BLUE – Ultramarine (from lapis lazuli stone), azurite (2CuCO₃·Cu(OH)₂); synthetic: ultramarine, Egyptian blue (CaCuSi₄O₁₀), cobalt blue (CoAl₂O₄), smalt (Co-glass) 
• BROWN – Earth pigments: brown ochre (α-Fe₂O₃+Mn-oxides), roasted umber (Fe₂O₃·xMnO₂), limonite (a mixture of various Fe-oxides) 
• BLACK – Manganite (γ-MnOOH), hausmannite (Mn₃O₄), iron black (magnetite, Fe₃O₄), graphite, charcoal, soot 
• METALLIC decorative pigments: aluminium (Al), copper (Cu), and brass (Cu+Zn) flakes 
• Earth pigments are not pure mineral pigments but various mixtures of clay, carbonates, and/or silica and several colour-carrying minerals, most commonly iron and manganese oxides.