Pigment

A pigment is a special chemical compound that gives color to things. It makes a substance or living thing look a certain color, or it can be used by people to add or change color. Unlike dyes, which dissolve in water, pigments do not dissolve easily and stay stable in their environment. They are usually made from inorganic materials, while dyes are often organic compounds.

Pigments have been important for a very long time. People used natural pigments like ochre, charcoal, and lapis lazuli to paint and decorate long ago. These colors came from the earth and stones and were very valuable. Today, pigments are still important in art, industry, and even in nature.

In living things, biological pigments are special compounds that give color to plants, animals, and other organisms. These pigments help protect living things, attract others, or even help them capture energy from the sun. Whether natural or made by people, pigments play a big role in the world around us.

Economic impact

In 2006, about 7.4 million tons of pigments were sold around the world. By 2018, the pigment industry was worth around $30 billion. One important pigment is titanium dioxide, which helps make many products bright white and is valued at $13.2 billion each year. Another famous color, Ferrari red, is worth about $300 million yearly. Organic pigments are mostly used in printing inks, paints, and coloring plastics and fabrics.

Physical principles

Main article: Spectroscopy

Pigments give color because they absorb certain wavelengths of visible light. The way the material is bonded decides which wavelengths of light are absorbed and which are reflected, and the reflected light is what gives us the color we see.

The color we see can also change depending on the light source. Sunlight, which has a high color temperature, is used as a standard for white light. Artificial lights can look different because they are less uniform. When we measure color using Lab color tools, we usually assume the light is like daylight, around a color temperature of 6500 K. Other substances mixed with pigments, like binders and fillers, can also change how saturated or light the color appears.

History

People have used minerals as colorful paints for thousands of years. Early humans painted their bodies and made cave art with natural pigments like ochre, which comes from iron oxide. Blue paint was made from a stone called lapis lazuli, and other colors came from places like Siena and Umbria, giving us names such as raw sienna and burnt umber.

Later, people learned to make their own pigments. One of the first was Egyptian blue, used in ancient Egypt. Over time, new colors like vermilion and Prussian blue were created. These advances let artists paint beautiful scenes with brighter, more consistent colors. Famous painters like Titian and Johannes Vermeer used these special pigments to make their paintings stand out.

Manufacturing and industrial standards

Before synthetic pigments were developed, batches of color were often inconsistent. Today, manufacturers and professionals work together to create international standards for identifying, producing, measuring, and testing colors.

The Munsell color system, first published in 1905, describes color in three dimensions: hue, value (lightness), and chroma (color purity). The International Organization for Standardization (ISO) develops technical standards for the manufacture of pigments and dyes, defining how to test for various industrial and chemical properties. Many manufacturers use the Colour Index International (CII) to identify pigments, resolving different names for the same pigment so everyone knows exactly what color they are working with.

Figures of merit

Pigments are judged on several important qualities that help decide how they can be used. One key quality is lightfastness, which measures how well a pigment can resist fading when exposed to sunlight or ultraviolet light. Another important trait is heat stability, indicating whether the pigment can remain unchanged when heated.

Other useful qualities include toxicity levels, how strongly a pigment can change the color of materials (tinting strength), and whether it can stick to surfaces (staining). Dispersion refers to how well the pigment spreads out, and this can be tested with a special tool called a Hegman gauge. Pigments are also evaluated for whether they are opaque (not letting light through) or transparent (letting light pass through). Finally, their ability to resist damage from substances like alkalis and acids, as well as how they interact with other pigments, are also important factors.

Swatches

Swatches help us see and share colors clearly. Different kinds of swatches are used for printing, computers, plastics, and textiles. Printed swatches, like PANTONE, RAL, and Munsell, are common standards for sharing colors in many areas such as printing and textiles.

For plastics, companies that make color masterbatches and pigments provide plastic swatches in colored chips. These chips help designers pick the right color for plastic products. They can even show special effects like pearl or metallic looks, though these are hard to show on screens or in prints.

On computers, showing the true color of pigments is tricky because screens can’t always match natural light. The Munsell Color System helps by measuring color in three ways: hue, lightness, and brightness. Even with careful settings, computer colors are just approximations and may not look exactly like the real pigment.

Biological pigments

Main article: Biological pigment

In biology, a pigment is any colored material found in plant or animal cells. Many parts of living things, such as skin, eyes, fur, and hair, contain pigments like melanin. Some animals, like the octopus and chameleon, can change their color using special cells called chromatophores.

Pigments help organisms in many ways, such as for camouflage, mimicry, warning signals, sexual selection, and photosynthesis in plants. Unlike structural color, which changes depending on the angle you look from, pigment color stays the same no matter where you view it from. For example, butterfly wings may have both structural color and pigment.

Pigments and polymers

Plastic colorants

Main article: Plastic colorant

Pigments are used to give plastics different colors for looks, selling better, and practical reasons. When choosing colors for plastics, it’s important to think about safety, the environment, and whether the pigment can be reused or disposed of properly.

Polymer pigments

Scientists have also worked on making polymers that act like pigments. Some common white pigments, such as titanium dioxide, can sometimes cause problems when used in paints because they are inorganic compounds. New hybrid pigments made from both organic and inorganic materials, like polymers and mica, have been created for use in cosmetics and coating applications.

Pigments by chemical composition

Pigments are often grouped by their chemical makeup into inorganic and organic types. Inorganic pigments, such as metal oxides and sulfides, have been used for a long time. Examples include barium white, cadmium yellow, carbon black, and iron oxide pigments like Venetian red and Prussian blue.

Organic pigments come from petrochemicals and have special molecular structures that give them color. Important organic pigments include phthalo blue, quinacridone, and indigo. Some of these were originally found in nature but are now made in laboratories.