There are today available a number of pigments. In fact after the advent of Synthetic Pigments there has evolved various classes of pigments that are suited to particular types of Industries.

Inorganic Pigments- They are of the type mineral-earth but generally are metallic oxides or synthetics. Pigments that are of the type Mineral-earth are very simple and naturally occurring colored substances. The preparation process is also simple and consists of the steps of washing drying, pulverizing and mixing into a formulation. The following table shows the refractive index of some of the very popular class of inorganic pigments.

Pigment	Refractive Index
TiO2 (rutile)	2.71
TiO2 (Anatase)	2.55
Antimony Oxide	2.20
Zinc Oxide	2.01
Calcium Carbonate	1.65
Fumed Silica	1.45

Examples of inorganic pigments can be materials like lead oxide, cobalt blue, chromium oxide, cadmium yellow, molybdate orange, and nickel titanate. As new environmental laws are very strict about toxicity a few of these heavy metal pigments are no longer in use.

Organic Pigments- Organic Pigments are not usually found in nature. That is the reason that a majority of these pigments are chemically synthesized. They contain carbon and comes with relatively low levels of toxicity, not providing any major environmental concern. Raw materials can include coal tar and petroleum distillates that are transformed into insoluble precipitates. Traditionally organic pigments are used as mass colourants. They are popular in plastics, synthetic fibers and as surface coatings-paints and inks. In recent years the organic pigments are used for hi-tech applications that includes photo-reprographics, opto-electronic displays and optical data storage.

Categories of Organic Pigments
Organic pigments are generally categorized into six types :

• Monoazo Pigments
• Diazo Pigments
• Acid and base dye Pigments
• Phthalocyanine Pigments
• Quinacridone Pigments
• Other polycyclic Pigments

Chemical structure of an Azo Pigment

Key features and characteristics of Organic Pigments

• Very good stability to solvents, light, heat, and weathering
• Good tinctorial strength
• Cost effectiveness
• Consistency and unique shades
• Completely non-toxic
• Very bright, pure, rich colors
• Organic pigments shows good color strength

As these days Metallic Pigments are a very popular category of Pigments, a further classification can be done for the metallic pigments.

Metallic pigments, can be of two types aluminum and zinc.

Aluminium Pigments: Aluminium pigments are further divided into two categories namely leafing grade and non-leafing grade. The aluminum pigments are produced from aluminium that has purity in the range of 99.3-99.97%. The particle has lamellar shape with 0.1-2 um in thickness and diameter of 0.5-200 um. These pigments founds use in automotive topcoats.

Some of the preferred applications of Aluminium Pigments are the following:

• As Corrosion protection coats
• As Reflective paints
• In Marine paints (covering coats)
• Roof coatings
• In Heat-proof and highly heat-resistance paints
• Chrome effect paints
• Aerosols

Zinc Pigments: Zinc Pigments come in two forms of powder and dust. Usually the zinc dust is finer as compared to powder and is spherical in shape. The dust also has a light coating of zinc oxide.

The following table cites some popular Zinc Pigments along with their applications.

Zinc Pigments	Application
Zinc dust	Chemical applications Metallurgical applications
Zinc phosphate	Active ingredient in domestic cleaning products
Zinc oxide	Agricultural applications Rubber industry Brick kilns Ceramics

Though every pigments has industrial application, but for understanding a few popular pigments have been given below that have very wide use.

Pearlescent CLC Pigments DPP Pigments Ultramarine Pigments Effect Pigments Fluorescent Pigments Inorganic Pigments Carbon Black Natural Pigments

Organic Pigments Organic vs Inorganic Pigments Mixed Metal Oxide Pigment Phosphorescent Pigment Intermediates Synthetic Iron Oxide Pigments Titanium Dioxide Natural Iron Oxide Pigments

The commercial performance of organic pigments are guided by the following capabilities:

• Coloristic performance
• Rheological behaviour
• Durability
• Ecological compatibility
• Tinctorial strength
• Opacity
• Resistance to heat