PIGMENTS -- PROVIDE COLOUR, HIDING AND BULK

Pigments are finely ground particles or powders which are dispersed in paints. Many of the same pigments are utilised in acrylic and oil-based paints.

There are two primary categories of pigments:

1.Prime pigments: These are the pigments that provide whiteness and colour; they are also the main source of hiding capability.

Titanium dioxide (TiO2), is the predominant white pigment. It 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(see section below) assures proper spacing of TiO2 particles to avoid crowding and loss of hiding, especially in flat and sheen paints
•has more chalking tendency in exterior paints than most colour and extender pigments

Colour pigments provide colour by selective absorption of light. There are two main types:

•Organic: These include the brighter colours, some of which are not highly durable in exterior use. Examples of organic pigments are phthalo blue and hansa yellow.
•Inorganic: Generally not as bright as organic colours (many are described as earth colours), these are the most durable exterior pigments. Examples of inorganic pigments are red iron oxide, brown oxide, ochers and umbers.

Colour pigments are compounded into liquid dispersions called colourants, which are added at the point of sale to tint bases, and to white paints designed for tinting. In the factory, colour pigments are used as dry powders and in liquid colourant form to make prepackaged colour paints.

2.Extender pigments (or "extenders") provide bulk at relatively low cost. They add much less hiding than TiO2, and impact on many properties, including sheen, scrub resistance, exterior colour retention, and others. Some commonly used extenders are:

•Clay: Aluminium silicates (also called kaolin and china clay) are used mainly in interior paints, but also in some exterior 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 control sheen in paints and varnishes.
•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--a relatively soft general purpose extender used in interior and exterior paints.
•Zinc oxide: This is a reactive pigment helpful with mildew resistance, corrosion inhibition and stain blocking. It is used mainly in primers and in exterior paints.