No.13: Pigments Used in Paints and Their Functions

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1. Types of Paint Pigments

Various pigments are used in paint to achieve its basic functions of protecting the surface and enhancing its appearance. These pigments are classified based on their function and composition. The table shows examples of such classifications. In this classification, the primary categories—coloring, extender, metallic, and anti-corrosive—focus on function. 

Here’s a brief explanation of each pigment. It is rare for paint to consist of only one pigment; usually, a combination of two to five pigments is used. Mixing pigments not only produces intermediate colors but also combines the characteristics of each to allow for the expression of delicate and complex designs, achieving a range of functionalities from beauty to rust prevention. 

2. Coloring Pigments 

Organic and inorganic pigments that absorb and scatter light are used to give paint its color and opacity. Organic pigments, based on carbon (and often containing oxygen, nitrogen, sulfur, or halogens, with some containing metal atoms), offer a variety of colors but are less durable. Inorganic pigments, while more durable, tend to have less vibrant colors. Colorless inorganic pigments, such as titanium dioxide white and carbon black, stand out for their depth of color. 

3. Extender Pigments

Some inorganic pigments are colorless and become transparent or translucent in paint, added mainly to reduce costs. However, they are also used to harden and add impact resistance to the paint film, and to adjust viscosity and specific gravity, as well as to modify color. These pigments range from synthetically manufactured to processed natural minerals. 

4. Metallic Pigments 

Pigment particles that are flake-shaped and orient parallel to the surface of the object they coat can significantly change the brightness and hue of the paint film depending on the viewing angle. This creates visual effects like metallic or pearl in the paint film. 

5. Anti-corrosive Pigments 

To prevent rust, inhibitors like phosphate ions and molybdate ions are released, protecting the painted object from corrosion. Lead and chromium, heavy metals previously widely used for their anti-corrosive properties, are now greatly restricted due to their toxicity.