How Pigments Work

Pigments selectively absorb wavelengths of light. When white light strikes a pigment molecule, there are different processes that can lead to absorption. Conjugated systems of double bonds absorb light in some organic pigments. Inorganic pigments may absorb light by electron transfer. For example, vermilion absorbs light, transferring an electron from the sulfur anion (S^2-) to a metal cation (Hg²⁺). The charge-transfer complexes remove most colors of white light, reflecting or scattering back the remainder to appear as a certain color. Pigments absorb or subtract wavelengths and do not add to them like luminescent materials do.

The spectrum of the incident light affects the appearance of a pigment. So, for example, a pigment won’t appear quite the same color under sunlight as it would under fluorescent lighting because a different range of wavelengths are left to be reflected or scattered. When the color of a pigment is represented, the lab light color used to take the measurement must be stated. Usually this is 6500 K (D65), which corresponds to the color temperature of sunlight.

The hue, saturation, and other properties of a pigment depend on other compounds that accompany it in products, such as binders or fillers. For example, if you purchase a color of paint, it will appear different depending on the formulation of the mixture. A pigment will look different depending on whether its final surface is glossy, matte, etc.

List of Significant Pigments

Pigments may be classified according to whether they are organic or inorganic. Inorganic pigments may or may not be metal-based. Here is a list of some key pigments:

Metallic Pigments

• Cadmium pigments: cadmium red, cadmium yellow, cadmium orange, cadmium green, cadmium sulfoselenide
• Chromium pigments: chrome yellow, viridian (chrome green)
• Cobalt pigments: cobalt blue, cobalt violet, cerulean blue, aureolin (cobalt yellow)
• Copper pigments: azurite, Egyptian blue, malachite, Paris green, Han purple, Han blue, verdigris, phthalocyanine green G, phthalocyanine blue BN
• Iron oxide pigments: red ochre, Venetian red, Prussian blue, sanguine, caput mortuum, oxide red
• Lead pigments: red lead, lead white, cremnitz white, Naples yellow, lead-tin yellow
• Manganese pigment: manganese violet
• Mercury pigment: vermillion
• Titanium pigments: titanium white, titanium black, titanium yellow, titanium beige
• Zinc pigments: zinc white, zinc ferrite

Other Inorganic Pigments

• Carbon pigments: carbon black, ivory black
• Clay earths (iron oxides)
• Ultramarine pigments (lapis lazuli): ultramarine, ultramarine green

Organic Pigments

• Biological pigments: alizarin, alizarin crimson, gamboge, cochineal red, rose madder, indigo, Indian yellow, Tyrian purple
• Non-biological organic pigments: quinacridone, magenta, diarylide yellow, phthalo blue, phthalo green, red 170