What are inorganic pigments？

Definition & Nature

Inorganic pigments are an important class of coloring materials, chemically compounds composed of colored metal oxides or insoluble metal salts. Unlike organic pigments, their core components are derived from inorganic substances, which determines their unique physical and chemical properties. Based on their source, inorganic pigments can be divided into two categories:

• Natural inorganic pigments:

These are mainly derived from mineral resources in nature and are produced through physical processing methods such as mining, screening, and crushing. Common varieties include cinnabar (mainly mercury sulfide), red clay (containing iron oxide), and realgar (arsenic sulfide). Due to the complex composition of natural minerals and the high content of impurities, these pigments generally have low purity, relatively dark color, and weak tinting power. However, they are low-cost and still have applications in some traditional fields.

• Artificial inorganic pigments (synthetic inorganic pigments) are produced by chemical synthesis and can be divided into two categories:

· Produced by purification and chemical processing of natural minerals;

· Produced through completely synthetic chemical reactions, such as precipitation, calcination, oxidation, etc. Synthetic inorganic pigments have a complete color spectrum, bright and vivid colors, and their hiding power and tinting strength are far superior to natural products. Typical representatives include titanium dioxide (titanium dioxide), chrome yellow (lead chromate), iron blue (ferric ferrocyanide), cadmium red (cadmium sulfide), etc.

Pigment Classification

Inorganic pigments can be classified from various perspectives. The table below is based on the system recommended by ISO and DIN. This system is based on color and chemical considerations. As is inevitable with many classification methods, there is overlap between categories, and clear boundaries are unlikely.

Pigment properties and composition

(1) Properties:

Inorganic pigments are light-resistant, heat-resistant, weather-resistant, solvent-resistant, and have strong hiding power, but their color spectrum is not very complete, their tinting strength is low, their color brilliance is poor, and some metal salts and oxides are highly toxic.

(2) Composition:

Inorganic pigments include various metal oxides, chromates, carbonates, sulfates, and sulfides, such as aluminum powder, copper powder, carbon black, zinc white, and titanium white, which all fall into the category of inorganic pigments.

Natural mineral pigments are completely derived from mineral resources, such as naturally produced cinnabar, red clay, realgar, etc. Synthetic ones include titanium dioxide, chrome yellow, iron blue, ruthenium red, ruthenium yellow, lithopone, carbon black, iron oxide red, iron oxide yellow, etc.

Pigment Classification & Applications

(1) Classification by Color: Inorganic coloring pigments can be divided into two categories: achromatic pigments and color pigments.

· Achromatic pigments include a range of pigments from white, gray to black, which only show differences in the amount of reflected light, that is, differences in brightness.

Color pigments can selectively absorb certain wavelengths of light and reflect the remaining wavelengths to produce a variety of different colors.

(2) Pigment Applications

Inorganic pigments are widely used in rubber, building materials, coatings, plastics, synthetic fibers, stationery, painting pigments, inks, papermaking, ceramics, glass, enamel and other industrial production sectors.

The History of Pigment Development

Inorganic pigments have a very long history of use. Early on, smoke black was the primary inorganic pigment, while its counterpart, chalk, was also a common pigment. Colored earth was also widely used, and natural iron oxide was also a common inorganic pigment.

· As early as 5,000 years ago, our ancestors were already regularly producing white lead.

· Approximately 2,300 years ago, my country had the technology to refine vermilion. However, other countries also achieved considerable success in pigment production.

· In the early 18th century, a German named Diesbach developed a method for producing Prussian blue. About a century later, Vauquelin of France invented a method for producing chrome yellow, and about 20 years later, Guimet of France produced ultramarine.

· Lithopone was developed in the 1870s. The subsequent advent of titanium composite pigments and methods for producing titanium dioxide promoted a significant advancement in the production of inorganic pigments.

· To date, the inorganic pigment spectrum has become essentially complete, with development focus shifting to improving performance, reducing environmental impact, and developing specialized functional pigments (such as those for corrosion protection, fluorescence, and temperature-sensitive properties). As a traditional and important material, inorganic pigments continue to play an indispensable role in industrial production and human life.