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Pigments for sale at a market stall in Goa, India

A pigment is a chemical compound that gives a substance or organism color, or is used by humans to add or alter color or change visual appearance. Pigments are completely or nearly insoluble and chemically unreactive in water or another medium; in contrast, dyes are colored substances which are soluble or go into solution at some stage in their use.[1][2] Dyes are often organic compounds whereas pigments are often inorganic. Pigments of prehistoric and historic value include ochre, charcoal, and lapis lazuli. Biological pigments are compounds produced by living organisms that provide coloration.

Economic impact

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In 2006, around 7.4 million tons of inorganic, organic, and special pigments were marketed worldwide.[3] According to an April 2018 report by Bloomberg Businessweek, the estimated value of the pigment industry globally is $30 billion. The value of titanium dioxide – used to enhance the white brightness of many products – was placed at $13.2 billion per year, while the color Ferrari red is valued at $300 million each year.[4]

Physical principles

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Main article: Spectroscopy
A wide variety of wavelengths (colors) encounter a pigment. This pigment absorbs red and green light, but reflects blue—giving the substance a blue-colored appearance.

Like all materials, the color of pigments arises because they absorb only certain wavelengths of visible light. The bonding properties of the material determine the wavelength and efficiency of light absorption.[5] Light of other wavelengths are reflected or scattered. The reflected light spectrum defines the color that we observe.

The appearance of pigments is sensitive to the source light. Sunlight has a high color temperature and a fairly uniform spectrum. Sunlight is considered a standard for white light. Artificial light sources are less uniform.

Color spaces used to represent colors numerically must specify their light source. Lab color measurements, unless otherwise noted, assume that the measurement was recorded under a D65 light source, or "Daylight 6500 K", which is roughly the color temperature of sunlight.

Sunlight encounters Rosco R80 "Primary Blue" pigment. The product of the source spectrum and the reflectance spectrum of the pigment results in the final spectrum, and the appearance of blue.

Other properties of a color, such as its saturation or lightness, may be determined by the other substances that accompany pigments. Binders and fillers can affect the color.

History

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Minerals have been used as colorants since prehistoric times.[6] Early humans used paint for aesthetic purposes such as body decoration. Pigments and paint grinding equipment believed to be between 350,000 and 400,000 years old have been reported in a cave at Twin Rivers, near Lusaka, Zambia. Ochre, iron oxide, was the first color of paint.[7] A favored blue pigment was derived from lapis lazuli. Pigments based on minerals and clays often bear the name of the city or region where they were originally mined. Raw sienna and burnt sienna came from Siena, Italy, while raw umber and burnt umber came from Umbria. These pigments were among the easiest to synthesize, and chemists created modern colors based on the originals. These were more consistent than colors mined from the original ore bodies, but the place names remained. Also found in many Paleolithic and Neolithic cave paintings are Red Ochre, anhydrous Fe2O3, and the hydrated Yellow Ochre (Fe2O3.H2O).[8] Charcoal—or carbon black—has also been used as a black pigment since prehistoric times.[8]

The first known synthetic pigment was Egyptian blue, which is first attested on an alabaster bowl in Egypt dated to Naqada III (circa 3250 BC).[9][10] Egyptian blue (blue frit), calcium copper silicate CaCuSi4O10, made by heating a mixture of quartz sand, lime, a flux and a copper source, such as malachite.[11] Already invented in the Predynastic Period of Egypt, its use became widespread by the 4th Dynasty.[12] It was the blue pigment par excellence of Roman antiquity; its art technological traces vanished in the course of the Middle Ages until its rediscovery in the context of the Egyptian campaign and the excavations in Pompeii and Herculaneum.[13] Later premodern synthetic pigments include white lead (basic lead carbonate, (PbCO3)2Pb(OH)2),[14] vermilion, verdigris, and lead-tin yellow. Vermilion, a mercury sulfide, was originally made by grinding a powder of natural cinnabar. From the 17th century on, it was also synthesized from the elements.[15] It was favored by old masters such as Titian. Indian yellow was once produced by collecting the urine of cattle that had been fed only mango leaves.[16] Dutch and Flemish painters of the 17th and 18th centuries favored it for its luminescent qualities, and often used it to represent sunlight.[citation needed] Since mango leaves are nutritionally inadequate for cattle, the practice of harvesting Indian yellow was eventually declared to be inhumane.[16] Modern hues of Indian yellow are made from synthetic pigments. Vermillion has been partially replaced in by cadmium reds.

Because of the cost of lapis lazuli, substitutes were often used. Prussian blue, the oldest modern synthetic pigment, was discovered by accident in 1704.[17] By the early 19th century, synthetic and metallic blue pigments included French ultramarine, a synthetic form of lapis lazuli. Ultramarine was manufactured by treating aluminium silicate with sulfur. Various forms of cobalt blue and Cerulean blue were also introduced. In the early 20th century, Phthalo Blue, a synthetic metallo-organic pigment was prepared. At the same time, Royal Blue, another name once given to tints produced from lapis lazuli, has evolved to signify a much lighter and brighter color, and is usually mixed from Phthalo Blue and titanium dioxide, or from inexpensive synthetic blue dyes.

The discovery in 1856 of mauveine, the first aniline dyes, was a forerunner for the development of hundreds of synthetic dyes and pigments like azo and diazo compounds. These dyes ushered in the flourishing of organic chemistry, including systematic designs of colorants. The development of organic chemistry diminished the dependence on inorganic pigments.[18]

  • Paintings illustrating advances in pigments
  • The Milkmaid by Johannes Vermeer (c. 1658). Vermeer was lavish in his choice of expensive pigments, including lead-tin yellow, natural ultramarine, and madder lake, as shown in the vibrant painting.[19]
    The Milkmaid by Johannes Vermeer (c. 1658). Vermeer was lavish in his choice of expensive pigments, including lead-tin yellow, natural ultramarine, and madder lake, as shown in the vibrant painting.[19]
  • Titian used the historic pigment vermilion to create the reds in the oil painting of Assunta, completed c. 1518.
    Titian used the historic pigment vermilion to create the reds in the oil painting of Assunta, completed c. 1518.
  • Miracle of the Slave by Tintoretto (c. 1548). The son of a master dyer, Tintoretto used Carmine Red Lake pigment, derived from the cochineal insect, to achieve dramatic color effects.
    Miracle of the Slave by Tintoretto (c. 1548). The son of a master dyer, Tintoretto used Carmine Red Lake pigment, derived from the cochineal insect, to achieve dramatic color effects.
  • Self Portrait by Paul Cézanne. Working in the late 19th century, Cézanne had a much broader palette of colors than his predecessors.
    Self Portrait by Paul Cézanne. Working in the late 19th century, Cézanne had a much broader palette of colors than his predecessors.

Manufacturing and industrial standards

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Natural ultramarine pigment in powdered form
Synthetic ultramarine pigment is chemically identical to natural ultramarine

Before the development of synthetic pigments, and the refinement of techniques for extracting mineral pigments, batches of color were often inconsistent. With the development of a modern color industry, manufacturers and professionals have cooperated to create international standards for identifying, producing, measuring, and testing colors.

First published in 1905, the Munsell color system became the foundation for a series of color models, providing objective methods for the measurement of color. The Munsell system describes a color in three dimensions, hue, value (lightness), and chroma (color purity), where chroma is the difference from gray at a given hue and value.

By the middle 20th century, standardized methods for pigment chemistry were available, part of an international movement to create such standards in industry. The International Organization for Standardization (ISO) develops technical standards for the manufacture of pigments and dyes. ISO standards define various industrial and chemical properties, and how to test for them. The principal ISO standards that relate to all pigments are as follows:

  • ISO-787 General methods of test for pigments and extenders.
  • ISO-8780 Methods of dispersion for assessment of dispersion characteristics.

Other ISO standards pertain to particular classes or categories of pigments, based on their chemical composition, such as ultramarine pigments, titanium dioxide, iron oxide pigments, and so forth.

Many manufacturers of paints, inks, textiles, plastics, and colors have voluntarily adopted the Colour Index International (CII) as a standard for identifying the pigments that they use in manufacturing particular colors. First published in 1925—and now published jointly on the web by the Society of Dyers and Colourists (United Kingdom) and the American Association of Textile Chemists and Colorists (US)—this index is recognized internationally as the authoritative reference on colorants. It encompasses more than 27,000 products under more than 13,000 generic color index names.

In the CII schema, each pigment has a generic index number that identifies it chemically, regardless of proprietary and historic names. For example, Phthalocyanine Blue BN has been known by a variety of generic and proprietary names since its discovery in the 1930s. In much of Europe, phthalocyanine blue is better known as Helio Blue, or by a proprietary name such as Winsor Blue. An American paint manufacturer, Grumbacher, registered an alternate spelling (Thanos Blue) as a trademark. Colour Index International resolves all these conflicting historic, generic, and proprietary names so that manufacturers and consumers can identify the pigment (or dye) used in a particular color product. In the CII, all phthalocyanine blue pigments are designated by a generic color index number as either PB15 or PB16, short for pigment blue 15 and pigment blue 16; these two numbers reflect slight variations in molecular structure, which produce a slightly more greenish or reddish blue.

Figures of merit

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The following are some of the attributes of pigments that determine their suitability for particular manufacturing processes and applications:

Swatches

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Swatches are used to communicate colors accurately. The types of swatches are dictated by the media, i.e., printing, computers, plastics, and textiles. Generally, the medium that offers the broadest gamut of color shades is widely used across diverse media.

Printed swatches

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Reference standards are provided by printed swatches of color shades. PANTONE, RAL, Munsell, etc. are widely used standards of color communication across diverse media like printing, plastics, and textiles.

Plastic swatches

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Companies manufacturing color masterbatches and pigments for plastics offer plastic swatches in injection molded color chips. These color chips are supplied to the designer or customer to choose and select the color for their specific plastic products.

Plastic swatches are available in various special effects like pearl, metallic, fluorescent, sparkle, mosaic etc. However, these effects are difficult to replicate on other media like print and computer display. Plastic swatches have been created by 3D modelling to including various special effects.

Computer swatches

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The appearance of pigments in natural light is difficult to replicate on a computer display. Approximations are required. The Munsell Color System provides an objective measure of color in three dimensions: hue, value (or lightness), and chroma. Computer displays in general fail to show the true chroma of many pigments, but the hue and lightness can be reproduced with relative accuracy. However, when the gamma of a computer display deviates from the reference value, the hue is also systematically biased.

The following approximations assume a display device at gamma 2.2, using the sRGB color space. The further a display device deviates from these standards, the less accurate these swatches will be.[20] Swatches are based on the average measurements of several lots of single-pigment watercolor paints, converted from Lab color space to sRGB color space for viewing on a computer display. The appearance of a pigment may depend on the brand and even the batch. Furthermore, pigments have inherently complex reflectance spectra that will render their color appearance[21][better source needed] greatly different depending on the spectrum of the source illumination, a property called metamerism. Averaged measurements of pigment samples will only yield approximations of their true appearance under a specific source of illumination. Computer display systems use a technique called chromatic adaptation transforms[22] to emulate the correlated color temperature of illumination sources, and cannot perfectly reproduce the intricate spectral combinations originally seen. In many cases, the perceived color of a pigment falls outside of the gamut of computer displays and a method called gamut mapping is used to approximate the true appearance. Gamut mapping trades off any one of lightness, hue, or saturation accuracy to render the color on screen, depending on the priority chosen in the conversion's ICC rendering intent.

#990024
Tyrian red
PR106 – #E34234
Vermilion (genuine)
#FFB02E
Indian yellow
PB29 – #003BAF
Ultramarine blue
PB27 – #0B3E66
Prussian blue

Biological pigments

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Main article: Biological pigment

In biology, a pigment is any colored material of plant or animal cells. Many biological structures, such as skin, eyes, fur, and hair contain pigments (such as melanin). Animal skin coloration often comes about through specialized cells called chromatophores, which animals such as the octopus and chameleon can control to vary the animal's color. Many conditions affect the levels or nature of pigments in plant, animal, some protista, or fungus cells. For instance, the disorder called albinism affects the level of melanin production in animals.

Pigmentation in organisms serves many biological purposes, including camouflage, mimicry, aposematism (warning), sexual selection and other forms of signalling, photosynthesis (in plants), and basic physical purposes such as protection from sunburn.

Pigment color differs from structural color in that pigment color is the same for all viewing angles, whereas structural color is the result of selective reflection or iridescence, usually because of multilayer structures. For example, butterfly wings typically contain structural color, although many butterflies have cells that contain pigment as well.

Pigments by chemical composition

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Phthalo Blue
Main article: List of inorganic pigments

Biological and organic

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See also

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Notes

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

Pigment

View on Grokipedia
from Grokipedia
A pigment is a colored , typically insoluble in water and common solvents, that imparts color to materials by selectively absorbing specific wavelengths of visible while reflecting or transmitting others. This property arises from the pigment's molecular structure, which determines its interaction with , distinguishing pigments from luminescent processes like . Pigments are dispersed as fine particles in a medium, such as binders in paints or polymers in plastics, to provide opacity, tint, or hue without dissolving. Unlike dyes, which are soluble and penetrate substrates to color them molecularly, pigments function through surface or incorporation, offering greater resistance to fading and washing in applications like coatings and textiles. They are classified primarily as organic or inorganic based on composition. Inorganic pigments, often metal-based compounds like oxides or sulfides (e.g., for whites or for greens), are prized for their , heat resistance, and opacity, making them suitable for industrial uses such as automotive paints and construction materials. Organic pigments, composed mainly of carbon, , , and oxygen, provide vibrant colors and transparency but can be less durable to light or chemicals; examples include azo compounds for yellows and reds, and they dominate in printing inks and artists' colors. Within these categories, pigments may be natural—sourced from minerals, , or animals (e.g., from )—or synthetic, engineered for consistency and performance. The history of pigments reflects innovation in color technology, beginning with natural inorganic varieties like red ochre and black manganese used in cave art dating back over 40,000 years. Ancient civilizations advanced extraction and grinding techniques, employing for blue in Egyptian and Mesopotamian works around 2500 BCE. The era of synthetic pigments dawned in 1704 with the accidental discovery of (ferric ), the first modern inorganic synthetic, revolutionizing accessibility and affordability for artists and industry. The saw explosive growth in organic colorants, such as the first synthetic dye in 1856, driven by the dye industry, enabling brighter, more stable colors for . In contemporary applications, pigments extend beyond aesthetics to functional roles, including UV protection in sunscreens, corrosion inhibition in coatings, and conductivity in electronics. Global production emphasizes sustainability, with research focusing on bio-based organics and low-toxicity inorganics to replace heavy metal variants like lead chromate. This evolution underscores pigments' indispensable role in art, manufacturing, and science, continually shaped by advances in chemical synthesis and environmental considerations.

Fundamentals

Definition and Classification

A pigment is a that imparts color, opacity, or other visual properties to a medium by absorbing specific wavelengths of visible , characterized as a that is insoluble in the application medium, such as , , or polymers, forming suspensions rather than solutions. Unlike dyes, which are soluble colorants that dissolve molecularly in the medium to produce transparent coloration, pigments remain dispersed as fine particles, providing greater opacity and durability in applications like paints, inks, plastics, and textiles. Pigments are primarily classified by origin into natural and synthetic categories. Natural pigments are derived directly from mineral, vegetable, or animal sources without chemical alteration, such as , a -based composed of iron oxides that has been used since for its red-yellow hues. Synthetic pigments, developed through industrial processes, offer consistent purity and vibrancy; for instance, charcoal black represents a carbon-based natural pigment obtained by charring wood, while modern synthetics expand this to controlled carbon variants. Another key classification is by chemical nature, distinguishing organic from inorganic pigments. Inorganic pigments typically contain metal ions or compounds, often sourced from minerals, providing stability and opacity; examples include iron oxide-based for earth tones. Organic pigments, composed primarily of carbon, , oxygen, and and often featuring conjugated systems, may include coordination complexes with metals; they yield brighter colors and are frequently synthetic, such as phthalocyanine blue, a copper-phthalocyanine complex used in high-performance coatings and inks for its intense blue shade and . Pigments are also categorized by function, encompassing colorants that primarily provide hue, fillers (or extenders) that enhance volume and mechanical properties without strong coloration, and functional additives that offer specialized effects like UV absorption to protect materials from degradation. For example, serves as both a white colorant and UV absorber in coatings, while inert fillers like reduce costs in plastics. The classification of pigments has evolved from early intuitive groupings based on source—such as , , or origins in ancient texts—to more systematic schemes incorporating and synthetic methods by the 19th and 20th centuries. This progression, driven by industrial advancements, shifted from utilitarian source-based lists to standardized taxonomies like those in the Colour Index, emphasizing reproducibility and performance.

Physical Principles

Pigments produce color through the selective absorption and reflection of wavelengths within the , typically ranging from 400 to 700 nm. When white interacts with a pigment particle, specific wavelengths are absorbed by the material's electronic structure, while others are reflected or transmitted, determining the perceived hue. For instance, a pigment appearing absorbs shorter wavelengths like and , reflecting longer wavelengths back to the observer. The key molecular features responsible for this absorption are , which are functional groups of atoms within the pigment that facilitate electronic transitions upon light exposure. In organic pigments, color arises from conjugated systems—alternating single and double bonds that delocalize pi electrons, lowering the energy gap required for visible light absorption and shifting the absorption from to visible regions. In contrast, inorganic pigments derive their color from various electronic transitions, including d–d ( field) transitions in compounds, charge-transfer transitions between metal and or between metals, and band-to-band transitions across the bandgap in semiconductors where the bandgap energy falls in the (typically producing colors from to red as the bandgap narrows). The intensity of absorption in pigment dispersions follows the Beer-Lambert law, which quantifies how light attenuation relates to pigment concentration and path , contributing to the material's opacity. The law is expressed as: A=ϵlcA = \epsilon l c where AA is the , ϵ\epsilon is the molar absorptivity (specific to the pigment and ), ll is the path through the medium, and cc is the concentration of the pigment particles. In pigment applications, such as coatings, this relationship models the cumulative absorption across multiple particle layers, predicting opacity buildup without light transmission. Beyond absorption, pigments exhibit including light and , which influence color perception and . occurs when light waves interact with pigment particles, redirecting them in various directions; the specifically describes the of shorter blue wavelengths by colloidal-sized particles (typically 10-1000 nm), enhancing perceived blueness in dilute suspensions. at particle surfaces can bend light paths, altering hue saturation. plays a critical role: larger particles (>500 nm) primarily scatter via reflection, yielding matte opacity, while smaller ones (<200 nm) promote diffraction, shifting colors toward shorter wavelengths and increasing transparency or iridescence due to wave interference. Unlike dyes, which dissolve molecularly in a medium to produce transparent solutions where light passes through with selective absorption, pigments remain insoluble particulates that scatter light extensively, resulting in inherent opacity even at low concentrations. This particulate nature prevents full light transmission, creating a suspended dispersion that masks underlying substrates.

Historical Development

Ancient and Traditional Pigments

The use of pigments dates back to prehistoric times, with evidence of pigment application dating back to approximately 100,000 years ago at in South Africa, where an ochre-based mixture was used for symbolic or artistic purposes. In Europe, cave paintings provide further examples, such as those in , France, dating to around 17,000 years ago, where red ochre derived from iron oxides was applied to depict animals and hand stencils. These early pigments were typically sourced from naturally occurring minerals, mixed with binders like animal fat or water to create rudimentary paints for wall decorations in protected caves. Among the key natural pigments employed in ancient and traditional art were earth colors, which originated from iron and manganese oxides found in clay deposits. Sienna, a yellowish-brown pigment in its raw form, was derived from iron oxide-rich soils in regions like Tuscany, while umber, darker and greener due to higher manganese content, was similarly extracted from natural earths and used for shading and depth in paintings. Lapis lazuli, ground into the vivid ultramarine blue, was primarily sourced from mines in Afghanistan's Badakhshan region dating back to the 7th millennium BCE, and its scarcity made it highly prized, especially during the Renaissance when it was reserved for depictions of the Virgin Mary's robes. Vermilion, a brilliant red obtained by grinding cinnabar (mercury sulfide, HgS), was valued for its intensity despite its toxicity from mercury content, and was applied in ancient Chinese lacquerware and Roman frescoes. Regional developments highlighted innovative sourcing and early synthesis of pigments. In ancient Egypt around 3000 BCE, malachite—a copper carbonate mineral—provided a bright green used in tomb decorations and cosmetics, while , the world's first known synthetic pigment made from copper compounds, silica, and lime, was fired into a stable frit for use in murals and jewelry. In Mesoamerica, the Maya and Aztecs extracted cochineal red from the dried bodies of female cochineal insects (Dactylopius coccus) farmed on prickly pear cacti, producing a potent carminic acid dye for textiles, pottery, and codices as early as 700 BCE. Trade routes significantly influenced pigment availability, with the Silk Road facilitating the transport of lapis lazuli from Afghan mines to Europe and the Mediterranean, where it became a luxury commodity exchanged alongside silk and spices from the 1st century BCE onward. Similarly, Tyrian purple, a dye-pigment hybrid derived from the glands of thousands of Mediterranean sea snails (primarily Bolinus brandaris), was produced by Phoenician artisans and traded at exorbitant costs—equivalent to three times the price of gold in the Roman era—due to the labor-intensive extraction process involving fermentation of up to 12,000 mollusks per gram. Pigments held profound cultural significance beyond aesthetics, often integral to rituals, mummification, and cosmetics. In ancient Egypt, red ochre and green malachite were applied during embalming to symbolize vitality and rebirth, while black kohl (from galena or soot) and green eye paints were used in funerary masks and daily adornments to invoke protection from evil spirits. These materials appeared in grave goods, such as palettes for grinding pigments, underscoring their role in ensuring safe passage to the afterlife and personal beautification rituals.

Modern and Synthetic Pigments

The development of modern synthetic pigments began in the early 18th century with the accidental discovery of in 1704 by Johann Jacob Diesbach, marking the first synthetic pigment with the chemical formula Fe₄[Fe(CN)₆]₃. This deep blue iron hexacyanoferrate compound revolutionized color production by offering a stable, reproducible alternative to natural blues like indigo or lapis lazuli, enabling its widespread use in paints, textiles, and prints. Its synthesis from simple inorganic precursors demonstrated the potential of chemical methods to surpass natural limitations in hue intensity and availability. In the 19th century, further milestones included the 1809 invention of chrome yellow (PbCrO₄), a lead chromate pigment that provided a vibrant, opaque yellow for industrial applications such as paints and ceramics. This compound's high tinting strength and lightfastness made it a staple in the burgeoning paint industry during the Industrial Revolution. A pivotal advancement came in 1856 when William Henry Perkin synthesized , the first synthetic organic pigment, through oxidation of aniline while attempting to produce quinine. This breakthrough ushered in the era of aniline-based colors, offering unprecedented vibrancy and scalability for textiles and later paints, fundamentally shifting pigment production from extraction to synthesis. The 20th century saw innovations driven by advances in inorganic and organic chemistry. Titanium dioxide (TiO₂), commercialized as a pigment in 1916, transformed white pigmentation by providing superior opacity and non-toxicity compared to lead white, becoming the dominant white pigment in paints and coatings due to its high refractive index and UV stability. In the 1930s, phthalocyanine pigments emerged, with copper phthalocyanine yielding brilliant, stable blues and greens that excelled in lightfastness and chemical resistance, widely adopted in automotive and printing industries. The 1880s introduction of azo pigments, derived from diazo coupling reactions in organic chemistry, expanded the palette with cost-effective reds, yellows, and oranges, enhancing color range while improving solubility and application versatility. Polymer science further bolstered pigment stability in the mid-20th century by enabling encapsulation and dispersion techniques in resin binders, reducing fading and improving adhesion in coatings. The transition to synthetic pigments accelerated post-1970s due to environmental regulations, such as the U.S. EPA's 1978 ban on lead-based paints, which prioritized consistency, lower cost, and non-toxicity over traditional lead chromates and whites. Synthetics like TiO₂ and organic alternatives offered uniform particle size for better dispersion and reduced health risks, driving their dominance in consumer and industrial products. This shift enhanced production efficiency while mitigating toxicity concerns associated with heavy metals. Recent developments through 2025 have focused on nanomaterials, bio-based synthetics, and advanced optoelectronics. Nano-scale TiO₂ particles, refined since the 2010s, enhance pigment durability in paints by improving UV resistance and mechanical strength, with studies showing up to 30% better weatherability in coatings. Bio-based synthetic pigments, derived from microbial fermentation or plant extracts via synthetic biology, offer sustainable alternatives to petroleum-derived organics; for instance, engineered azaphilone pigments provide stable reds and purples with reduced environmental footprint. As of 2025, EU regulations have accelerated adoption of such bio-pigments in coatings, reducing reliance on synthetic organics by up to 20% in compliant industries. Quantum dot pigments, semiconductor nanocrystals like CdSe or InP, have advanced display technologies by 2025, enabling QLED screens with over 90% color gamut coverage and enhanced brightness for vibrant, energy-efficient visuals. These innovations prioritize sustainability and performance, addressing demands for eco-friendly, high-impact coloration.

Chemical Composition

Inorganic Pigments

Inorganic pigments are colored materials derived from minerals or synthetic metal compounds that impart color through their crystalline or amorphous structures, primarily used in applications requiring durability. These pigments are typically insoluble in common solvents and include classes such as metal oxides, sulfides, and chromates. Examples of metal oxides include iron(III) oxide (Fe₂O₃), which produces red hues due to its hematite structure, and zinc oxide (ZnO), a white pigment valued for its opacity. Sulfides like cadmium sulfide (CdS) yield bright yellow colors, while chromates such as lead chromate (PbCrO₄) have been historically used for yellow pigments but are now largely phased out due to environmental regulations. The color of inorganic pigments arises from electronic transitions influenced by crystal structures, lattice defects, and metal-ligand interactions within the solid matrix. In many cases, transition metal ions in specific coordination environments absorb visible light, leading to perceived color; for instance, in the spinel structure of cobalt aluminate (CoAl₂O₄), known as cobalt blue, the tetrahedral coordination of Co²⁺ ions causes d-d transitions that produce an intense blue hue. Lattice defects, such as vacancies or impurities, can further modulate the bandgap and absorption spectrum, enhancing color intensity or shifting wavelengths. Inorganic pigments offer advantages including exceptional thermal stability, resistance to chemicals and light, and long-term durability, making them suitable for harsh environments like outdoor coatings. However, they often contain heavy metals, leading to potential toxicity concerns; for example, cadmium- and lead-based pigments pose environmental and health risks upon release. Titanium dioxide (TiO₂) exemplifies structural variations affecting properties, with the rutile polymorph providing superior UV protection compared to anatase due to its higher refractive index and lower photocatalytic activity, which prevents degradation in polymer matrices. Carbon black, an amorphous form of elemental carbon (C), serves as a non-metal inorganic black pigment with high tinting strength and UV absorption, though it lacks a crystalline lattice. Identification of inorganic pigments commonly employs X-ray diffraction (XRD), which analyzes crystalline structures to distinguish phases like rutile from anatase or confirm spinel compositions, enabling precise characterization without sample destruction.

Organic Pigments

Organic pigments are carbon-based colorants derived from organic compounds, distinguished by their molecular structures that enable vibrant hues through conjugation and electronic transitions. These pigments encompass both synthetic and naturally occurring varieties, with synthetic ones dominating modern applications due to their tunable properties. Unlike inorganic pigments, which rely on crystal lattices for color, organic pigments achieve coloration primarily through delocalized pi-electron systems in their molecular frameworks. The core structures of organic pigments include azo compounds, polycyclic types, and phthalocyanines. Azo pigments, comprising about 59% of organic pigments, feature a central -N=N- azo linkage (Ar-N=N-Ar) flanked by aromatic rings, as seen in Hansa yellow (Pigment Yellow 1), which provides bright yellow tones. Polycyclic pigments, such as quinacridone reds and perylenes, consist of fused ring systems offering high stability and intense reds to violets; for instance, quinacridone (Pigment Violet 19) derives from anthraquinone scaffolds. Phthalocyanines, though often metal-complexed (e.g., copper phthalocyanine blue, Pigment Blue 15), are classified as organic due to their macrocyclic porphyrin-like cores, delivering deep blues and greens with exceptional durability. Natural organic pigments include indigo, a plant-derived indoxyl dimer with the formula C16_{16}H10_{10}N2_{2}O2_{2}, extracted from Indigofera species for blue shades, and alizarin, an anthraquinone (C14_{14}H8_{8}O4_{4}) from madder root (Rubia tinctorum), renowned for its red dyeing properties. Organic pigments exhibit high tinting strength, allowing small quantities to impart intense color, and often superior transparency compared to inorganic counterparts, making them ideal for glazing and metallic effects. However, they face challenges in lightfastness, typically rated using the ASTM scale (I excellent to V poor) or the Blue Wool scale (1-8, with 8 excellent). Development of these pigments advanced through diazotization in azo synthesis, where aromatic amines are converted to diazonium salts via nitrous acid, followed by coupling with activated aromatics to form the azo bond; this process, established in the late 19th century, enabled mass production of vibrant synthetics. Modern high-performance organic pigments, like diketopyrrolopyrrole (DPP) reds, are engineered for automotive coatings, providing weather-resistant, transparent colors that meet stringent OEM standards for durability and gloss. Lake pigments represent a hybrid form where organic dyes are precipitated onto inorganic substrates like alumina or calcium salts to enhance insolubility and handling. For example, madder lake is produced by adsorbing alizarin from madder root extracts onto aluminum hydroxide, yielding a stable red pigment used historically in art and textiles. This method improves the pigment's resistance to bleeding while retaining the dye's vividness.

Biological Aspects

Pigments in Nature

Pigments in nature are ubiquitous across living organisms, serving as essential components for light absorption, protection, and signaling, with diverse chemical structures derived from biosynthetic pathways. These naturally occurring pigments exhibit a wide range of colors and functions, primarily categorized by their molecular frameworks such as porphyrins, carotenoids, flavonoids, and melanins. In plants, chlorophylls are the predominant green pigments, consisting of magnesium-porphyrin complexes that enable photosynthesis by absorbing red and blue wavelengths of light while reflecting green. Chlorophyll a and b, the most common variants, are localized in chloroplasts and are crucial for capturing solar energy in leaves, stems, and algae. Carotenoids, another major class, include β-carotene, an orange tetraterpenoid that acts as an accessory pigment in photosynthesis and provides antioxidant properties to protect against oxidative stress; these are found in roots, fruits, and flowers, contributing to yellow, orange, and red hues. Anthocyanins, water-soluble flavonoids, produce red, purple, and blue colors in flowers, fruits, and leaves, with their hue shifting based on pH—appearing red in acidic conditions and blue in alkaline ones—due to structural changes in their anthocyanidin core. Animal pigments often derive from modified amino acids or heme breakdown products, providing coloration for integumentary structures. Melanins are polymeric pigments synthesized from tyrosine, with eumelanin producing black to brown shades through indolequinone units for UV protection and structural integrity in skin, hair, and eyes, while pheomelanin yields red-yellow tones via benzothiazine intermediates, commonly seen in feathers and fur. Bilins, linear tetrapyrroles derived from heme catabolism, include biliverdin and bilirubin; biliverdin imparts green or blue colors to bird eggshells and insect exoskeletons, serving as a waste product with antioxidant roles, whereas bilirubin appears yellow in certain vertebrates. Microbial pigments display remarkable diversity, particularly in bacteria adapted to extreme environments. Bacteriochlorophylls, analogous to plant chlorophylls but with reduced porphyrin rings, are magnesium-containing bacteriochlorins that facilitate anoxygenic photosynthesis in purple and green sulfur bacteria, absorbing infrared light for energy capture in low-oxygen habitats. Prodigiosin, a red tripyrrole pigment produced by Serratia marcescens and other gammaproteobacteria, features a tripyrrole structure consisting of three pyrrole rings and is secreted extracellularly, often in response to environmental stressors. The extraction of natural pigments has ancient roots, with early human societies utilizing plant sources for dyes; for instance, henna (Lawsonia inermis) yields lawsone, a red-orange naphthoquinone extracted from leaves, used since at least 2500 BCE in ancient Egypt and India for body art and fabric coloration through simple aqueous or acidic processing. Evolutionarily, natural pigments have played key roles in adaptation, with chlorophylls emerging early in photosynthetic lineages to harness light for energy, carotenoids aiding in photoprotection and signaling ripeness in fruits to attract dispersers, and animal melanins and bilins evolving for camouflage against predators or mating displays through sexual selection, as seen in the vivid carotenoid-based plumage of birds that balances concealment and conspicuousness.

Functions and Applications

Biological pigments serve essential roles in organisms, primarily facilitating energy capture, sensory perception, and protection against environmental stressors. In plants, enables photosynthesis by absorbing light energy, particularly in the blue and red wavelengths, to convert carbon dioxide and water into glucose and oxygen, supporting plant growth and oxygen production in the atmosphere. Carotenoids, another key class of pigments, act as accessory pigments in photosynthesis while also functioning as antioxidants to neutralize reactive oxygen species generated during light exposure, thereby preventing cellular damage in plants and animals. In animals, pigments contribute to vision and defense mechanisms. The retinal pigment epithelium (RPE) in the eye absorbs stray light and supports the visual cycle by recycling retinal, a vitamin A derivative essential for phototransduction in rod and cone cells, enabling light detection and image formation. Melanin, concentrated in skin, hair, and eyes, provides ultraviolet (UV) radiation shielding by absorbing UV photons and dissipating energy as heat, reducing DNA damage and the risk of skin cancer in humans and other vertebrates. Animal adaptations often leverage pigments for survival and communication. Structural coloration arises from nanoscale structures interacting with pigments, producing iridescence in peacock feathers through thin-film interference that reflects specific wavelengths, aiding mate attraction and species recognition without relying solely on chemical pigments. Aposematic coloration uses bright pigments, such as those in poison dart frogs, to signal toxicity or unpalatability to predators, enhancing survival by promoting learned avoidance behaviors. Extracted biological pigments find applications in human health and industry. Beta-carotene, sourced from carrots and other vegetables, serves as a natural food colorant and vitamin A precursor in supplements, helping prevent deficiency-related conditions like night blindness in populations with limited dietary intake. In cosmetics, carmine derived from cochineal insects provides a stable red hue for lipsticks and blushes, approved by regulatory bodies for safe use in external applications. Curcumin, a yellow pigment from turmeric, exhibits anti-inflammatory effects by inhibiting pathways like NF-κB and COX-2, supporting its use in pharmaceuticals for managing conditions such as arthritis and metabolic syndrome. Advancements in biotechnology have expanded pigment applications through genetic engineering. The improved Golden Rice 2, developed in the mid-2000s and approved for release in the Philippines in 2021, incorporates a maize-derived psy gene along with a bacterial gene for carotenoid biosynthesis into rice endosperm, producing beta-carotene (23–35 μg/g dry weight) to combat vitamin A deficiency in rice-dependent regions. Regulatory approval was granted in the Philippines in 2021, with commercial distribution beginning in 2022; as of 2025, it is being distributed in rice-dependent regions, though adoption faces challenges from anti-GMO sentiments. Despite these benefits, extracting biological pigments poses sustainability challenges. Astaxanthin from microalgae like Haematococcus pluvialis requires resource-intensive cultivation and extraction processes, leading to high costs and environmental concerns from energy use in production, prompting research into more efficient, eco-friendly methods to avoid overexploitation of natural sources.

Production and Properties

Manufacturing Processes

The manufacturing of inorganic pigments typically involves precipitation, calcination, and milling to achieve desired chemical composition and particle characteristics. In the sulfate process for (TiO₂), a prominent white pigment, ilmenite ore is digested with concentrated sulfuric acid to form titanyl sulfate, which is then hydrolyzed in water to precipitate hydrated (TiO₂·nH₂O). This precipitate is filtered, washed to remove impurities, and subsequently calcined at temperatures around 800–1000°C to dehydrate and form the anhydrous rutile or anatase crystal structure. Calcination, a high-temperature decomposition step, is essential for many inorganic pigments, including complex inorganic colored pigments (CICPs) such as spinel or zircon-based oxides, where precursor mixtures of metal salts or oxides are heated to 1000–1400°C in a solid-state reaction to form stable, heat-resistant crystals with vibrant colors. Following synthesis, milling—often using ball mills, attritors, or classifier mills—reduces particle size and breaks down agglomerates, ensuring uniform dispersion and optimal light-scattering properties for applications like paints and coatings. Organic pigments are synthesized through targeted chemical reactions tailored to their molecular structures. Azo pigments, which dominate the yellow, orange, and red color ranges, are produced via azo coupling, where an aromatic primary amine is diazotized with sodium nitrite in acidic conditions to form a diazonium salt, which then reacts with an electron-rich coupling component such as a naphthol or amine to yield the colored azo compound; this process is conducted at controlled temperatures (0–5°C for diazotization) to prevent decomposition. For phthalocyanine pigments like copper phthalocyanine blue (Pigment Blue 15), the synthesis involves cyclization of phthalic anhydride with urea and a copper(II) salt (e.g., copper chloride) under high-temperature conditions (150–250°C) in the presence of a catalyst like ammonium molybdate, forming the macrocyclic structure in a solvent such as nitrobenzene or via a solvent-free fusion method. Post-processing steps refine raw pigments for industrial compatibility and performance. Dispersion involves incorporating the pigment powder into liquid vehicles (e.g., resins or solvents) using high-shear mixers or bead mills to create stable suspensions that prevent settling and ensure even color distribution in end products. Surface treatments, such as coating with silane coupling agents (e.g., triethoxycaprylylsilane), modify the pigment surface to enhance compatibility with organic binders, improve hydrophobicity, and reduce agglomeration by forming covalent bonds between inorganic particles and polymer matrices. Micronization further controls particle size to a typical range of 1–10 μm through techniques like jet milling or fluidized-bed mills, optimizing opacity, tinting strength, and flow properties while minimizing dust and improving handling. Quality control in pigment manufacturing relies on spectroscopic techniques to verify purity and consistency. Techniques such as near-infrared (NIR) spectroscopy and Fourier-transform infrared (FTIR) spectroscopy analyze molecular composition and detect impurities non-destructively, enabling real-time monitoring of reaction progress and final product specifications like color strength and absence of contaminants. Environmental considerations address waste from hazardous processes, such as the traditional mercury-based production of vermilion (cinnabar, HgS); mercury-free alternatives include cadmium red (PR108) or modern organic pigments like pyrrole red (PR254), which replicate the hue without toxic heavy metals. The scale of pigment production has evolved from batch reactors, common in early 20th-century methods, to continuous flow processes post-1950s, particularly for high-volume pigments like TiO₂ via the chloride process and azo dyes, enabling higher throughput, reduced waste, and consistent quality through automated control of reaction parameters.

Figures of Merit

Figures of merit for pigments encompass standardized metrics that quantify their performance in applications such as paints, coatings, and inks, enabling comparisons of quality, efficiency, and suitability across formulations. These metrics evaluate aspects like color development, coverage, durability, and handling properties, often through protocols established by organizations such as ASTM International and the International Organization for Standardization (ISO). By focusing on these quantifiable attributes, manufacturers and users can select pigments that meet specific end-use requirements without relying on subjective assessments. Tinting strength refers to a pigment's capacity to impart color to a medium, such as a vehicle or binder, and is typically measured relative to a standard pigment under controlled conditions. This property is crucial for determining how efficiently a pigment can achieve desired hues with minimal quantity, influencing formulation costs and color consistency. For white pigments, tinting strength is assessed visually by comparing the color of a tint (pigment mixed with a standard blue pigment) against a reference, as outlined in ASTM D332. In practice, higher tinting strength allows for brighter, more saturated colors at lower concentrations, with measurements often involving spectrophotometric analysis for precision in chromatic pigments. Hiding power, also known as opacity, measures a pigment's ability to obscure or cover an underlying substrate, preventing the background color from showing through the applied layer. It is particularly important in coatings where uniform appearance over varied surfaces is required, such as in architectural paints. Hiding power is quantified using the contrast ratio, defined as R=Rb−RwRb+RwR = \frac{R_b - R_w}{R_b + R_w}, where RbR_b and RwR_w represent the reflectance of the coating over black and white substrates, respectively; a value approaching 1 indicates near-complete opacity. This metric is evaluated through reflectometry in standards like ASTM D2805, which applies to liquid paints and assesses hiding at a specified film thickness. Lightfastness evaluates a pigment's resistance to color fading upon exposure to light, a critical factor for longevity in indoor and outdoor applications. It is commonly rated on the , ranging from 1 (least resistant, fades quickly) to 8 (highly resistant, minimal change after prolonged exposure), based on comparison to standardized blue-dyed wool references under controlled illumination. This scale is formalized in ISO 105-B02, which simulates daylight exposure using xenon arc or filtered mercury lamps. For exterior uses, weatherfastness extends lightfastness to include effects from moisture, temperature cycles, and UV radiation, often tested via accelerated weathering protocols that correlate to real-world durability. Additional metrics include dispersibility, which assesses the ease with which a pigment incorporates into a medium without agglomeration, influencing uniformity and processing efficiency; this is evaluated through methods like Hegman gauge fineness of grind or dynamic light scattering for particle distribution. Bleed resistance measures a pigment's tendency to migrate or dissolve into adjacent layers or solvents, preventing color bleeding in multi-layer coatings, and is tested by solvent extraction as per ASTM D279. Toxicity indices, such as the median lethal dose (LD50), quantify acute safety, with values exceeding 5000 mg/kg (oral, rat) indicating low mammalian toxicity for many commercial pigments, derived from standardized or EPA guidelines. Testing standards from ISO and ASTM provide the frameworks for these evaluations, ensuring across laboratories. For instance, the oil absorption value, expressed in grams of oil per gram of pigment, indicates the amount of vehicle required to wet the pigment particles fully, affecting and properties; it is determined by spatula rub-out in ASTM D281 or mechanical kneading in ASTM D1483. These protocols, part of broader series like ISO 787 for general pigment tests, allow for batch-to-batch consistency and performance prediction in end products.

Industrial and Practical Uses

Standards and Specifications

The (CI) system serves as the global standard for classifying dyes and pigments, assigning unique identifiers based on chemical constitution and color properties to ensure consistency across industries. For instance, Pigment Blue 15 (PB15) designates blue, a widely used organic pigment valued for its stability and tinting strength. Safety regulations govern pigment use to mitigate health and environmental risks, with the European Union's REACH framework (Regulation (EC) No 1907/2006) restricting hazardous substances, including certain azo pigments that may release carcinogenic aromatic amines under Annex XVII, entry 43. In the United States, the (FDA) approves pigments for food-contact materials under 21 CFR Parts 70-82 and 178.3297, requiring safety demonstrations for colorants in packaging to prevent migration into . Industry-specific standards address performance in targeted applications; for example, ASTM D476 classifies dry pigmentary products into types suitable for architectural and automotive coatings based on composition and opacity. In , ISO 12647 specifies process parameters for color reproduction in offset , including ink density and hue targets for pigment-based formulations to achieve standardized output. Purity specifications emphasize contaminant control and physical properties, with the Ecological and Toxicological Association of Dyes and Organic Pigments Manufacturers (ETAD) recommending limits such as less than 100 ppm for lead in organic pigments to minimize risks. Particle size distributions are standardized via ASTM D1366, which outlines reporting methods like mean diameter and percentiles to predict dispersion and optical performance in formulations. International harmonization has advanced post-2020 through updates promoting sustainable pigments, including bio-renewable content requirements tested under ASTM D6866, which measures biobased carbon percentages to support eco-friendly alternatives in global supply chains.

Visual Representation and Swatches

Printed swatches serve as standardized physical representations of pigment colors, typically in the form of cards or books where pigments are applied as inks on substrates. These swatches account for substrate absorption, which influences the final color appearance by affecting how pigments interact with the 's surface and fibers. The Matching System (PMS), for instance, provides such printed guides with specific formulations to ensure consistent reproduction across printing processes. Plastic and material swatches offer representations tailored to non-paper media, often created as molded samples in polymers like to demonstrate pigment dispersion effects within solid matrices. These are particularly useful in design fields for visualizing how pigments behave in coatings and plastics, where light scattering and alter color . The RAL Plastics standard exemplifies this approach, using multifunctional plates to translate traditional shades into plastic-compatible formats for precise communication in . Digital swatches represent pigment colors through computational models in design software, commonly using RGB for screen displays or CMYK for print simulations. Tools like Adobe Color allow users to generate and save these swatches, converting between color spaces while preserving relative hues. However, digital representations face gamut limitations, as RGB can encompass a broader range of colors than CMYK, leading to inaccuracies when translating vibrant pigment shades to print. Additionally, metamerism poses a challenge, causing colors to shift under different lighting conditions due to discrepancies between digital simulations and physical pigment . To achieve precise pigment color matching, measures reflected light across the , enabling calculations of s in standardized spaces like CIE Lab. In this system, the ΔE quantifies perceptual variance between samples using the formula: ΔE=ΔL2+Δa2+Δb2\Delta E = \sqrt{\Delta L^2 + \Delta a^2 + \Delta b^2}
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