Inert Pigment

Definition - What does Inert Pigment mean?

Inert pigment refers to a pigment, extender or adultrant that does not change the shade or hue of a paint, but extends or otherwise imparts various physical properties other than color, such as opacity or texture. An inert pigment does not chemically react with the materials with which it is being mixed.

Inert pigments are mainly fillers; when used in excess, they can be regarded as adulterants. Inert pigments should be used in the lowest possible concentration required to get the maximum color concentration in paints.

Inert pigments are also known as inerts, fillers and extenders.

Corrosionpedia explains Inert Pigment

Inert pigments are pigments that become colorless in the vehicle in which they are mixed, such as chalk gypsum, barium white and the like in oil paints. They are used as a foundation for lake pigments, or as extenders or adulterant for colored pigments.

The functions of inert pigments include:

  • To occupy volume in a film
  • To adjust the rheological properties of fluid coatings and the gloss
  • To balance the mechanical properties of films

The most commonly used inerts are chalk or calcium carbonate (CaCO3) pigments. These pigments should not be used in exterior latex paints because they can cause a frosting of insoluble calcium carbonate deposited on the film. In dark colored paints, frosting can be seen. A variety of clay (aluminum silicates), mica (aluminum potassium silicate) and magnesium silicate minerals are also used as inert pigments. Inert pigments are mostly inorganic minerals but organic materials, such as powdered polypropylene, can also be used as inert pigments.

Inerts are added to paints to control the tinting strength or hiding power of the paints.

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