WHAT IS PIGMENT COLOR

 

WHAT IS PIGMENT COLOR

PIGMENT COLOR

Pigment color refers to the color of an object or substance that is derived from the selective absorption and reflection of light by pigments present in or on that object. Pigments are substances that absorb certain wavelengths of light while reflecting others, and the color we perceive is the result of the wavelengths of light that are reflected in our eyes.

The color of a pigment is determined by its chemical composition and the specific wavelengths of light it absorbs and reflects. For example, a red pigment absorbs most wavelengths of light except for those in the red part of the spectrum, which it reflects, giving the appearance of a red color.

Pigments are commonly used in various applications, including paints, dyes, inks, and cosmetics, to achieve specific colors. They are also found naturally in many living organisms, including plants, animals, and microorganisms, where they play a role in coloration and various biological functions.

 

Pigments for sale at a market stall in Goa, India

A pigment is a colored substance that is completely or nearly insoluble in water. 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.

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.

Physical principles

A wide variety of wavelengths (colors) encounter a pigment. This pigment absorbs red and green light but reflects blue-giving the substance a blue-colored appearance.

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. Light of other wavelengths is 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.

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. 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). 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. 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 and 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.^[13] Later premodern synthetic pigments include white lead (basic lead carbonate, (PbCO₃)₂Pb(OH)₂), 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. By the early 19th century, synthetic and metallic blue pigments included French ultramarine, a synthetic form of lapis lazuli. Ultramarine was manufactured by treating aluminum 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 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. The development of organic chemistry diminished the dependence on inorganic pigments.

·         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.

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.

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 modeling to include 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.^[20] 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 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 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