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 nearly or completely 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. 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 In 2006, around 7.4 million tons of inorganic, organic, and special pigments were marketed worldwide. 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. For organic pigments, the major application is printing inks followed by paints and coloring plastics and textiles.
Physical principles
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.Thomas B. Brill, Light: Its Interaction with Art and Antiquities, Springer 1980, p. 204 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.
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 Minerals have been used as colorants since prehistoric times. 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. 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). Charcoal—or carbon black—has also been used as a black pigment since prehistoric times.
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).Lorelei H. Corcoran, "The Color Blue as an 'Animator' in Ancient Egyptian Art", in Rachael B.Goldman, (ed.), Essays in Global Color History: Interpreting the Ancient Spectrum (New Jersey: Gorgias Press, 2016), pp. 59–82. Egyptian blue (blue frit), is calcium copper silicate CaCuSi4O10, made by heating a mixture of quartz sand, lime, a flux and a copper source, such as malachite. Already invented in the Predynastic Period of Egypt, its use became widespread by the 4th Dynasty. 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. Later premodern synthetic pigments include white lead (basic lead carbonate, (PbCO3)2Pb(OH)2),Lead white at ColourLex 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. 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. Dutch and Flemish painters of the 17th and 18th centuries favored it for its luminescent qualities, and often used it to represent sunlight. Since mango leaves are nutritionally inadequate for cattle, the practice of harvesting Indian yellow was eventually declared to be inhumane. 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.Prussian blue at ColourLex 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.
Manufacturing and industrial standards
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.
Processing Pigments are typically produced as primary particles. These primary particles may fuse across their surfaces to form aggregates. The term agglomerates refers to primary particles and/or aggregates joined at their corners or edges. During the dispersion process, these pigment agglomerates are fractured as the pigments are incorporated into an application medium, resulting in smaller agglomerates, aggregates, and primary particles. Once formed, these are wetted by a dispersing medium and, ideally, achieve a uniform statistical distribution throughout the application medium.
In solid form, pigments can be used in their pure state (primary pigment), as a solid blend of two or more pigments, or as a mixture with one or more fillers. Mixing with fillers reduces color strength, allowing for more precise dosing of small quantities—a practice commonly employed in powder coatings. Due to spatial proximity, primary pigments exhibit enhanced intensity (simultaneous contrast).
For liquid coatings, pre-dispersed pigment preparations—which may be binder-based or binder-free—are frequently used. These preparations are formulated similarly to the coating itself; they are pre-dispersed and contain high pigment concentrations within additives, solvents, water, or binders, depending on the application. The primary advantage of pigment preparations lies in their simple and precise incorporation, as the pigment is already dispersed and standardized. However, certain additives may be disadvantageous if the preparation is incompatible with specific coating systems.
A tinting system consists of a combination of several (typically 12–20) pigment preparations, an automatic dosing system, and formulation software. This method is standard for emulsion paint. Pigment preparations may exist as mixtures with other pigments or fillers. In addition to common liquid preparations, granulated versions made with highly soluble binders are available for applications where additional solvents are undesirable in the paint formulation.