So what exactly is pigment?

As pigments, the most immediate impression they give us is color—coloring being their most fundamental property. Humanity’s pursuit of color dates back to prehistoric times; over 60,000 years ago, people were already using natural ochre as a coloring material.

Structurally, pigments consist of tiny colored particles formed by molecules with specific crystal structures. They are insoluble in water, oil, solvents, and resins, yet can be uniformly dispersed within these media. Their coloration arises from optical phenomena such as light reflection, scattering, absorption, or transmission by the pigment particles. Consequently, crystal particle size and crystal structure critically influence color expression. For instance, effect pigments like aluminum powder and pearlescent pigments exhibit enhanced shimmering effects with greater light-reflecting capacity.

Due to their shared characteristics of covering power, tinting strength, and relative light stability, they are commonly referred to as “colorants.” It is important to note that pigments differ from dyes: dyes are typically soluble in water or solvents and are primarily used for textile dyeing, whereas pigments are used in a dispersed state. However, exceptions exist, such as certain insoluble dyes and pigments suitable for textile printing and solution dyeing, which blur the distinction between the two. Due to their structural similarity to organic dyes, organic pigments are often regarded as a subcategory of dyes.

The Evolution of Pigments

The history of human use of inorganic pigments stretches back millennia. Cave paintings from tens of thousands of years ago already employed natural materials like charcoal, ochre, manganese brown, and kaolin. Around 2000 BCE, people began firing natural ores mixed with manganese ore to produce red, purple, and black hues for pottery. Orpiment and orpimentite were among the first vivid yellow pigments, while ultramarine and Egyptian blue represented early blue hues. Greens were derived from verdigris and malachite. White pigments commonly utilized calcite, calcium sulfate, or kaolin.

Pigment diversity remained largely unchanged until the late Middle Ages. The Renaissance brought new developments, such as the introduction of carmine from Mexico to Europe, followed by the emergence of cobalt blue and cobalt-blue glass. From the 18th century onward, industrially produced pigments like Prussian blue, cobalt blue, and chrome yellow gradually appeared. The 19th century saw the development of chrome green, iron oxide-based, and cadmium-based pigments. The 20th century saw accelerated research, yielding synthetic red pigments, manganese blue, molybdenum red, and bismuth-based mixed oxides. Concurrently, white pigments like rutile and anatase titanium dioxide and needle-shaped zinc oxide gained prominence, alongside effect pigments producing metallic, pearlescent, and interference colors.

Primary Applications of Pigments

Pigments find extensive use across diverse industries, including coatings, plastics, rubber, cosmetics, textiles, ceramics, and artistic cement coloring. Their applications continue to expand into new fields such as cosmetics, food, adhesives, and electrostatic copying. Selecting the appropriate pigment type is critical, requiring a comprehensive evaluation of its performance, effects, and cost-effectiveness to leverage its strengths while mitigating weaknesses for optimal utilization.

Categories of Pigments

Pigments can be broadly classified into three main categories: organic pigments, inorganic pigments, and effect pigments.

· Organic Pigments: These include azo pigments, polycyclic pigments, and metal complexes, among others, and can be further subdivided based on chemical structure;

· Inorganic Pigments: include bismuth vanadate, chromates, chromium oxides, iron oxides, titanium dioxide, carbon black, zinc compounds (zinc oxide, zinc sulfide), ultramarine, iron blue (Prussian blue, Chinese blue), and hybrid metal oxides;

· Effect pigments: Categorized into interference-type (e.g., mica-based pearlescent pigments) and reflective-type (e.g., aluminum silver paste).

Performance Comparison of Different Types of Pigments

Characteristics	Organic Pigments	Inorganic Pigments	Effect Pigments
Chroma (Saturation)	High	Poor	Moderate
Tinting Strength	High	Low	Low
Transparency	Good	Poor	Poor
Hiding Power	Poor	Excellent	Good
Weather Resistance	Limited	Excellent	Good
Solvent Resistance	Limited	Excellent	Excellent
Flocculation Stability	Poor	Good	Excellent
Dispersibility	Poor	Good	Good
Thermal Stability	Limited	Excellent	Good
Density	Low	High	High
Particle Size	Small	Large	Large

Primary Application Areas

Plastics, inks, coatings, textiles

Architectural coatings, ceramics, paints

Automotive coatings, decorative coatings, cosmetics

In summary, pigments not only boast a long history and diverse range but also continuously drive technological innovation and application expansion, becoming indispensable functional materials across multiple industries.