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Pigment

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For the drug referred to as "pigment," see black tar heroin.
The monarch butterfly's distinctive pigmentation serves as a warning to potential predators, many of which have evolved to recognize the butterfly and avoid predation, because the monarch butterfly is poisonous.
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The monarch butterfly's distinctive pigmentation serves as a warning to potential predators, many of which have evolved to recognize the butterfly and avoid predation, because the monarch butterfly is poisonous.




The Blue Morpho butterfly, native to Central America, derives its distinctive blue coloring from iridescence rather than from pigmentation.

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The Blue Morpho butterfly, native to Central America, derives its distinctive blue coloring from iridescence rather than from pigmentation.










 An anonymous prehistoric cave painter used naturally occurring ochres and oxides of iron and manganese to depict paleolithic fauna at Lascaux, France.

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An anonymous prehistoric cave painter used naturally occurring ochres and oxides of iron and manganese to depict paleolithic fauna at Lascaux, France.










Titian used the historic pigment Vermilion to create the reds in the great fresco of Assunta, completed about 1518.

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Titian used the historic pigment Vermilion to create the reds in the great fresco of Assunta, completed about 1518.







In biology, pigment is any material resulting in color of plant or animal cells, which is the result of selective color absorption. Pigment color differs from structual color in that it is the same for all viewing angles, whereas structural color is the result of selective reflection or iridescence, usually done with multilayer structures.  Many biological structures, such as skin, eyes, fur and hair contain pigments (such as melanin) in specialized cells called chromatophores. Butterfly wings typically contain structural color, although many of them contain pigment as well. Creatures which lack pigmentation are called albinos. 


In manufacturing and in the visual arts, a pigment is a dry colorant, usually ground into a fine powder.  Pigments are used for coloring paint, inks, plastic, fabric, and other materials. Pigments work by selectively absorbing some parts of the visible spectrum (see light) while reflecting others. 


A distinction is usually made between a pigment, which is insoluble in the vehicle (or matrix), and a dye, which is either a liquid, or is soluble. A certain colorant can also be both a pigment and a dye depending on in which vehicle it is used. Fugitive pigments are non-permanent pigments, often because they are unstable when exposed to heat or higher wavelengths of visible or ultraviolet light.


In some cases, a pigment can be manufactured by precipitating a soluble dye with a metallic salt. The metallic salt used must be very inert and insoluble in the vehicle.  The salt that is commonly chosen is barium sulfate, which is also used as a white filler pigment, and can be produced from an inexpensive mineral called barite. The resulting pigment is called a lake. 





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History of pigments


Naturally occurring pigments such as ochres and iron oxides have been used as colorants since prehistoric times.  Archaeologists have uncovered evidence that 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.  


Before the 18th century, the range of color available for art and decorative uses was technically limited.  Most of the pigments then in use were earth and mineral pigments or pigments of biological origin. Some colors could only be collected and manufactured at great expense.  Colors that were costly to produce, such as blue and purple, became associated with royalty. 


The Industrial and Scientific Revolutions brought a huge expansion in the range of synthetic pigments, pigments that are manufactured or refined from naturally occurring materials, available both for manufacturing and artistic expression. 


Historically and culturally, many famous natural pigments have been replaced with modern synthetic pigments, while retaining their historic names. In some cases the original color name has shifted in meaning, as a historic color name has been applied to a popular modern color. By convention, a contempory replacement for a historic pigment name is generally indicated by calling the color a hue, but manufacturers are not always careful in maintaining this distinction. The following examples illustrate the shifting nature of historic pigment color names:



Manufacturing and Industrial Standards


The International Organization for Standardization (ISO) develops technical standards for the manufacture of pigments and colors. 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:




Other published ISO standards relate 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, Phthalo Blue 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 (Thalo 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 Phthalo Blue pigments are designated by a generic colour index number as either PB15 or PB36, short for pigment blue 15 and pigment blue 36. (The two forms of Phthalo Blue, PB15 and PB36, reflect slight variations in molecular structure that produce a slightly more greenish or reddish blue.)



Scientific and Technical Issues


Selection of a pigment for a particular application is determined both by cost, and by the physical properties and attributes of the pigment itself. For example, a pigment that is used to color glass must have very high heat stability in order to survive the manufacturing process, but suspended in the glass vehicle, its resistance to alkali or acid materials is not an issue. In an artist paint, heat stability is less important, while lightfastness and toxicity are greater concerns. 


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





Biological pigments




Non-Biological pigments



References





External links


































 




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