Pigment
A pigment is a colored material that is completely or nearly insoluble in water.[1][2] 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 ochre, charcoal, and lapis lazuli.
pigment
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.[7] 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.
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).[11][12] 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.[13] Already invented in the Predynastic Period of Egypt, its use became widespread by the 4th Dynasty.[14] 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.[15] Later premodern synthetic pigments include white lead (basic lead carbonate, (PbCO3)2Pb(OH)2),[16] 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 Vermilion, a mercury sulfide, was originally made by grinding a powder of natural cinnabar.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.[17] 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.[18] 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.[18] 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.[19] 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.[20]
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.[21]
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.
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:
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.
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.
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.[22] 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[23][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[24] 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.
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.
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.
In the final revised risk determination, EPA found unreasonable risk to workers and occupational non-users from PV29 as a whole-chemical substance. The conditions of use that drive the whole chemical unreasonable risk determination are the same as the January 2021 risk evaluation: domestic manufacturing and import of the chemical; processing (incorporation into formulation, mixture or reaction products in paints, coatings, plastic and rubber products; use as an intermediate for other perlyene pigments; and recycling); industrial/commercial use in paint and coatings in the automobile sector, and merchant ink for commercial printing; and disposal. Risks to workers, including occupational non-users, can come from long-term inhalation exposure. These risks drive the whole chemical determination of unreasonable risk to human health.
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