Pigment

A pigment is a colored material that is completely or nearly insoluble in water, and or most solvents. In contrast, dyes are typically soluble, at least at some stage in their use. Generally dyes are often organic compounds whereas pigments are often inorganic compounds, though exceptions to this rule exist.

General

Like all materials, the color of pigments arises because they absorb only certain wavelengths of visible light, while reflecting or scattering the other wavelengths. The bonding properties of the material determine the wavelength and efficiency of light absorption. The reflected light spectrum defines the color that we observe.

Common pigments by color

• White: Barium sulfate, Titanium dioxide (titanium white), zinc oxide (zinc white);
• Red: Iron(III) oxide (red ochre), cadmium sulfoselenide (Red Cadmium), mercury sulfide (cinnabar, vermilion), tetraarsenic tetrasulfide (realgar), cerium(III) sulfide (α- and β-Ce₂S₃), Lead(II,IV) oxide (minium/red lead);
• Orange: Lead(II,IV) oxide (minium/orange lead), cadmium sulfoselenide (Pigment Orange 20), chrome orange (Pb2CrO5), molybdate orange (PbCrO4·PbMoO4·PbSO4), bismuth vanadate orange;
• Yellow: Cadmium sulfide (cadmium yellow), As₂S₃ (orpiment), Primrose yellow (PY184) (bismuth vanadate), yellow ochre (Fe2O3•H2O), Lead-tin-yellow (PbSnO4), zinc chromate (zinc yellow);
• Green: Chrome green (anhydrous chromium(III) oxide), viridian (hydrated chromium(III) oxide), cobalt green, malachite (cupric carbonate hydroxide), Scheele's Green (copper arsenite);
• Blue: Ultramarine, lapis lazuli/Persian blue, cobalt blue (cobalt(II) aluminate), Cerulean blue (cobalt(II) stannate), Egyptian blue (calcium copper silicate), Han blue (barium copper silicate), azurite (cupric carbonate hydroxide), Prussian blue, YInMn Blue;
• Purple: Cobalt violet (cobalt phosphate), Manganese violet (manganic ammonium pyrophosphate NH4MnP2O7), Han purple (BaCuSi2O6), Purple of Cassius (Gold nanoparticles suspended in tin(II) oxide);
• Black: Amorphous carbon/graphite, magnetite (Fe3O4), manganese dioxide, titanium(III) oxide (titanium black), elemental boron;

Availability

Pigments can be bought from various hardware or art stores. They can also be acquired online.

Preparation

Pigments can be prepared by chemical means or by grounding up bulk material.

Projects

• Make ceramic glazing
• Painting

Handling and safety

Pigments containing heavy metals (except barium) may be harmful, and should be handled with care.

Storage and disposal

Pigments in general are not volatile, thus can be kept in any clean bottle. Most pigments don't require special disposal, though heavy metal pigments should be taken to waste disposal facilities.

See also

• Charcoal
• Dye

References

Relevant Sciencemadness threads

• Paint creation thread
• Pigments in the art world, for love of brightly colored compounds
• pigments as a source for chemicals
• Synthesis of Pigments For Oil Paints
• Synthesizing YInMn Blue in my kitchen, and breaking antique equipment in the process
• Viridian pigments
• Fluorescent Pigment Powder and liquid
• UV pigment powder