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Details of Pigment

A pigment is a material that changes the color of light it reflects as the result of selective color absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which the material itself emits light. Many materials selectively absorb certain wavelengths of light. Materials that humans have chosen and developed for use as pigments usually have special properties that make them ideal for coloring other materials. A pigment must have a high tinting strength relative to the materials it colors. It must be stable in solid form at ambient temperatures.

For industrial applications, as well as in the arts, permanence and stability are desirable properties. Pigments that are not permanent are called fugitive. Fugitive pigments fade over time, or with exposure to light, while some eventually blacken.

Pigments are used for coloring paint, ink, plastic, fabric, cosmetics, food and other materials. Most pigments used in manufacturing and the visual arts are dry colourants, usually ground into a fine powder. This powder is added to a vehicle (or matrix), a relatively neutral or colorless material that acts as a binder.

A distinction is usually made between a pigment, which is insoluble in the vehicle (resulting in a suspension), and a dye, which either is itself a liquid or is soluble in its vehicle (resulting in a solution). A colorant can be both a pigment and a dye depending on the vehicle it is used in. In some cases, a pigment can be manufactured from a dye by precipitating a soluble dye with a metallic salt. The resulting pigment is called a lake pigment.

Physical basis

A wide variety of wavelengths (colors) encounter a pigment. This pigment absorbs red and green light, but reflects blue, creating the color blue.

Pigments appear the colors they are because they selectively reflect and absorb certain wavelengths of light. White light is a roughly equal mixture of the entire visible spectrum of light. When this light encounters a pigment, some wavelengths are absorbed by the chemical bonds and substituents of the pigment, and others are reflected. This new reflected light spectrum creates the appearance of a color. Ultramarine reflects blue light, and absorbs other colors. Pigments, unlike fluorescent or phosphorescent substances, can only subtract wavelengths from the source light, never add new ones.

The appearance of pigments is intimately connected to the color of the source light. Sunlight has a high color temperature, and a fairly uniform spectrum, and is considered a standard for white light. Artificial light sources tend to have great peaks in some parts of their spectrum, and deep valleys in others. Viewed under these conditions, pigments will appear different colors.

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.

Color spaces used to represent colors numerically must specify their light source. Lab color measurements, unless otherwise noted, assume that the measurement was taken 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 added to pure pigment chemicals also have their own reflection and absorption patterns, which can affect the final spectrum. Likewise, in pigment/binder mixtures, individual rays of light may not encounter pigment molecules, and may be reflected as is. These stray rays of source light contribute to the saturation of the color. Pure pigment allows very little white light to escape, producing a highly saturated color. A small quantity of pigment mixed with a lot of white binder, however, will appear desaturated and pale, due to the high quantity of escaping white light.

Pigment groups

• Arsenic pigments: Paris Green
• Carbon pigments: Carbon Black, Ivory Black, Vine Black, Lamp Black
• Cadmium pigments: cadmium pigments, Cadmium Green, Cadmium Red, Cadmium Yellow, Cadmium Orange
• Iron oxide pigments: Caput Mortuum, oxide red, Red Ochre, Sanguine, Venetian Red, Mars Black
• Prussian blue
• Chromium pigments: Chrome Green, Chrome Yellow
• Cobalt pigments: Cobalt Blue, Cerulean Blue, Cobalt Violet, Aureolin
• Lead pigments: lead white, Naples yellow, Cremnitz White, red lead
• Copper pigments: Paris Green, Verdigris, Viridian, Egyptian Blue, Han Purple
• Titanium pigments: Titanium White, Titanium Beige, Titanium yellow, Titanium Black
• Ultramarine pigments: Ultramarine, Ultramarine Green Shade, French Ultramarine
• Mercury pigments: Vermilion
• Zinc pigments: Zinc White
• Clay earth pigments (which are also iron oxides): Raw Sienna, Burnt Sienna, Raw Umber, Burnt Umber, Yellow Ochre.
• Lapis lazuli,
• Biological origins: Alizarin, Alizarin Crimson, Gamboge, Indigo, Indian Yellow, Cochineal Red, Tyrian Purple, Rose madder
• Other Organic: Pigment Red 170, Phthalo Green, Phthalo Blue, Quinacridone Magenta.

Biological pigments

The monarch butterfly's distinctive pigmentation reminds potential predators that it is poisonous.

Main article: Biological pigment

In biology, a pigment is any material in color of plant or animal cells. Many biological structures, such as skin, eyes, fur and hair contain pigments (such as melanin) in specialized cells called chromatophores. Many conditions affect the levels or nature of pigments in plant and animal cells. For instance, Albinism is a disorder affecting the level of melanin production in animals.

Pigment color differs from structural colour in that it 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.

History

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 Industrial Revolution, the range of color available for art and decorative uses was technically limited. Most of the pigments in use were earth and mineral pigments, or pigments of biological origin. Pigments from unusual sources such as botanical materials, animal waste, insects, and mollusks were harvested and traded over long distances. Some colors were costly or impossible to mix with the range of pigments that were available. Blue and purple came to be associated with royalty because of their expense.

Biological pigments were often difficult to acquire, and the details of their production were kept secret by the manufacturers. Tyrian Purple is a pigment made from the mucus of one of several species of Murex snail. Production of Tyrian Purple for use as a fabric dye began as early as 1200 BCE by the Phoenicians, and was continued by the Greeks and Romans until 1453 CE, with the fall of Constantinople. The pigment was expensive and complex to produce, and items colored with it became associated with power and wealth. Greek historian Theopompus, writing in the 4th century BCE, reported that "purple for dyes fetched its weight in silver at Colophon [in Asia Minor]."

Mineral pigments were also traded over long distances. The only way to achieve a deep rich blue was by using a semi-precious stone, lapis lazuli, to produce a pigment known as ultramarine, and the best sources of lapis were remote. Flemish painter Jan Van Eyck, working in the 15th century, did not ordinarily include blue in his paintings. To have one's portrait commissioned and painted with ultramarine blue was considered a great luxury. If a patron wanted blue, they were forced to pay extra. When Van Eyck used lapis, he never blended it with other colors. Instead he applied it in pure form, almost as a decorative glaze.^[3] The prohibitive price of lapis lazuli forced artists to seek less expensive replacement pigments, both mineral (azurite, smalt) and biological (indigo).

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.

Spain's conquest of a New World empire in the 16th century introduced new pigments and colors to peoples on both sides of the Atlantic. Carmine, a dye and pigment derived from a parasitic insect found in Central and South America, attained great status and value in Europe. Produced from harvested, dried, and crushed cochineal insects, carmine could be used in fabric dye, body paint, or in its solid lake form, almost any kind of paint or cosmetic.

Natives of Peru had been producing cochineal dyes for textiles since at least 700 CE,^[4] but Europeans had never seen the color before. When the Spanish invaded the Aztec empire in what is now Mexico, they were quick to exploit the color for new trade opportunities. Carmine became the region's second most valuable export next to silver. Pigments produced from the cochineal insect gave the Catholic cardinals their vibrant robes and the English "Redcoats" their distinctive uniforms. The true source of the pigment, an insect, was kept secret until the 18th century, when biologists discovered the source.^[5]

Girl with a Pearl Earring by Johannes Vermeer (c. 1665).

While Carmine was popular in Europe, blue remained an exclusive color, associated with wealth and status. The 17th century Dutch master Johannes Vermeer often made lavish use of lapis lazuli, along with Carmine and Indian Yellow, in his vibrant paintings.