Pigment

A pigment is a colored material that is completely or nearly insoluble in water.[1] 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. Pigments of prehistoric and historic value include ocher, charcoal, and lapis lazuli.

Pigments for sale at a market stall in Goa, India.


Economic impact

In 2006, around 7.4 million tons of inorganic, organic and special pigments were marketed worldwide.[2] estimated at around US$14.86 billion in 2018 and will rise at over 4.9% CAGR from 2019 to 2026.[3] The global demand on pigments was roughly US$20.5 billion in 2009.[4] 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.[5]

Physical principles
Main article: Spectroscopy
A wide variety of wavelengths (colors) encounter a pigment. This pigment absorbs red and green light, but reflects blue—creating the color blue.

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.[6] Light of other wavelengths are reflected or scattered. The reflected light spectrum defines the color.

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

Minerals have been used as colorants since prehistoric times.[7] 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.[8] 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).[9] Charcoal—or carbon black—has also been used as a black pigment since prehistoric times.[9]

Synthetic pigments were introduced as early as the second millennium BCE.[10] White lead (basic lead carbonate, (PbCO3)2Pb(OH)2) is one of example.[11] and blue frit (Egyptian Blue). Another early synthetic pigment is blue frit, calcium copper silicate, made by heating glass with a copper source, such as malachite. Later premodern synthetic pigments include vermilion, verdigris, and lead-tin-yellow. Vermilion, a mercury compound, 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.[12] 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.[12] Modern hues of Indian yellow are made from synthetic pigments. Vermillion has been parttially replaced in by cadmium reds.

Because of the expense of lapis lazuli, much effort went into finding a less costly blue pigment. This search was partly satisfied by Prussian blue, discovered by accident in 1704.[13] 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 and Cerulean blue were also introduced. In the early 20th century, Phthalo Blue, a synthetic metallo-organicc 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 dye, 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.s. The development of organic chemistry diminished the dependence on inorganic pigments.[14]

  • 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.[15]
  • 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.
  • 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 standard
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 (USA)—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

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

  • Lightfastness and sensitivity for damage from ultraviolet light
  • Heat stability
  • Toxicity
  • Tinting strength
  • Staining
  • Dispersion (which can be measured with a Hegman gauge)
  • Opacity or transparency
  • Resistance to alkalis and acids
  • Reactions and interactions between pigments

Swatches

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

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

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

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.[16] 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[17] 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[18] 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
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), as well as 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 elemental composition
Phthalo Blue
Main article: List of inorganic pigments


Biological and organic
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See also

Notes
  1. Völz, Hans G.; Kischkewitz, Jürgen; Woditsch, Peter; Westerhaus, Axel; Griebler, Wolf-Dieter; De Liedekerke, Marcel; Buxbaum, Gunter; Printzen, Helmut; Mansmann. "Pigments, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a20_243.pub2.
  2. Pigments Market size
  3. Market Study Pigments, 3rd ed., Ceresana, 11/13. Archived 3 September 2010 at the Wayback Machine
  4. "Market Report: World Pigment Market". Acmite Market Intelligence. Archived from the original on 29 November 2010.
  5. Schonbrun, Zach (18 April 2018). "The Quest for the Next Billion-Dollar Color". Bloomberg Businessweek. Retrieved 2 May 2018.
  6. Thomas B. Brill, Light: Its Interaction with Art and Antiquities, Springer 1980, p. 204
  7. St. Clair, Kassia (2016). The Secret Lives of Colour. London: John Murray. pp. 21, 237. ISBN 9781473630819. OCLC 936144129.
  8. "Earliest evidence of art found". BBC News. 2 May 2000. Archived from the original on 3 June 2016. Retrieved 1 May 2016.
  9. "Pigments Through the Ages". WebExhibits.org. Archived from the original on 11 October 2007. Retrieved 18 October 2007.
  10. Rossotti, Hazel (1983). Colour: Why the World Isn't Grey. Princeton, NJ: Princeton University Press. ISBN 0-691-02386-7.
  11. Lead white Archived 25 December 2015 at the Wayback Machine at ColourLex
  12. "History of Indian yellow". Pigments Through the Ages. Archived from the original on 21 December 2014. Retrieved 13 February 2015.
  13. Prussian blue Archived 2 January 2016 at the Wayback Machine at ColourLex
  14. Simon Garfield (2000). Mauve: How One Man Invented a Color That Changed the World. Faber and Faber. ISBN 0-393-02005-3.
  15. Johannes Vermeer, The Milkmaid Archived 14 April 2015 at the Wayback Machine, ColourLex
  16. "Dictionary of Color Terms". Gamma Scientific. Archived from the original on 20 August 2014. Retrieved 25 June 2014.
  17. "Color Appearance". Hello Artsy.
  18. "Chromatic Adaptation". cmp.uea.ac.uk. Archived from the original on 29 September 2007. Retrieved 16 April 2009.
  19. Engineer Manual 1110-2-3400 Painting: New Construction and Maintenance (PDF). 30 April 1995. pp. 4–12. Archived (PDF) from the original on 1 December 2017. Retrieved 24 November 2017.

References
  • Ball, Philip (2002). Bright Earth: Art and the Invention of Color. Farrar, Straus and Giroux. ISBN 0-374-11679-2.
  • Doerner, Max (1984). The Materials of the Artist and Their Use in Painting: With Notes on the Techniques of the Old Masters, Revised Edition. Harcourt. ISBN 0-15-657716-X.
  • Finlay, Victoria (2003). Color: A Natural History of the Palette. Random House. ISBN 0-8129-7142-6.
  • Gage, John (1999). Color and Culture: Practice and Meaning from Antiquity to Abstraction. University of California Press. ISBN 0-520-22225-3.
  • Meyer, Ralph (1991). The Artist's Handbook of Materials and Techniques, Fifth Edition. Viking. ISBN 0-670-83701-6.
  • Feller, R. L., ed. (1986). Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 1. London: Cambridge University Press.
  • Roy, A., ed. (1993). Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 2. Oxford University Press.
  • Fitzhugh, E. W., ed. (1997). Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 3. Oxford University Press.
  • Berrie, B., ed. (2007). Artists' Pigments. A Handbook of Their History and Characteristics, Vol. 4. Archetype Books.
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