Pigments
Provide color or whiteness, hiding, bulk, and corrosion resistance

Pigments are finely ground particles or powders that are dispersed in paints. Many of the same pigments are utilized in waterborne acrylic and solventborne paints.
There are three primary categories of pigments used in industrial coatings: prime, extender, and inhibitive.

PRIME PIGMENTS: These are the pigments that provide the color and whiteness. They are also the main source of hiding capability. Titanium dioxide (TiO2) is the predominant white pigment, which has these characteristics:
• provides exceptional whiteness by scattering light
• provides whiteness and hiding in flat or glossy paint, whether wet, dry
   or rewetted
• is relatively expensive
• use of appropriate extender ensures proper spacing of TiO2 particles
   to avoid crowding and loss of hiding, especially in flat and satin paints
• has more chalking tendency in exterior paints than most color and
   extender pigments.

Color pigments provide color by selective absorption of light. There are two main types: organic and inorganic.

• Organic: These include the brighter colors, some of which are not highly durable in exterior use. Examples of organic pigments are phthalocyanine blue and Hansa yellow.

• Inorganic: Generally not as bright as organic colors (many are described as earth colors), these are the most durable exterior pigments. Examples of inorganic pigments are red iron oxide, brown oxide, ochers and umbers.
Color pigments are compounded into liquid dispersions called colorants, which are added at the point of sale to tint bases, and to white paints designed for tinting. In the factory, color pigments are used as dry powders and in liquid colorant form to make pre-packaged color paints.

EXTENDER PIGMENTS: Also called extenders, these provide bulk at relatively low cost. They add much less hiding than TiO2 and impact on many properties, including gloss, color retention and corrosion resistance. Some commonly used extenders are noted below:

• Clay: Aluminum silicates (also called kaolin and china clay) are mainly
   used in interior paints. Calcined (heated to drive off water and create
   air-particle interfaces) clay provides more hiding than most extenders;
   delaminated clay enhances stain resistance.
• Silica and Silicates: These provide scrub and abrasion resistance.
   Many of these exhibit excellent durability in exterior paints.
• Diatomaceous Silica: This is a form of hydrous silica consisting of
   ancient fossilized single-cell organisms. It is used to limit sheen in
   paints and varnished.
• Calcium Carbonate: Also called chalk, this is a general purpose, low cost,
   low hiding pigment used in both interior and exterior paints.
• Talc: Magnesium silicate, this is a relatively soft, general purpose
   extender used in interior and exterior paints.

INHIBITIVE PIGMENTS: Also referred to as reactive or anti-corrosive pigments, they assist in preventing corrosion of metal substrates. They are usually employed in primers and direct-to-metal (DTM) coatings. Inhibitive pigments containing lead and chromate were historically used for their superb effectiveness, but due to environmental and health concerns, other types are now used. These include zinc oxide, zinc phosphate and modified zinc phosphates, as well as borates, molybdates, phosphates and phosphosilicates based on zinc, aluminum, calcium and other metals. Organic corrosion inhibitors are also used.

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