Pigments:
Pigments are insoluble inorganic or organic coloring substances. Pigments are used in dispersions and, essentially, physically, chemically unaffected by the media it is dispersed. Different pigments can be mixed together to create different colors, such as purple and blue. There is no black or brown pigment - these two colors are created by mixing the primary colors together.
Classification of pigment
There are many types of pigments that can be used in a variety of applications. Some of the most common pigment types are described below.
- Inorganic
- Organic
- Metal
Inorganic Pigments:
Inorganic pigments are made from non-carbon materials. They are generally less expensive than organic pigments, but they have poorer colorfastness properties. The body, Covering power, the intensity, the lightfastness etc of the inorganic pigments are always superior to organic pigment. Furthermore, inorganic pigments are more economical than organic pigments.
Organic pigments:
Organic pigments are made from carbon-containing materials. They are generally more expensive than inorganic pigments, but they have better colorfastness properties. Organic color pigments are generally brighter and richer in color. They are generally more susceptible to degrading and destructive influences like sunlight, chemical attack and bleeding.
Metal Pigments:
Metal pigments are made from metal compounds. They have excellent colorfastness and durability properties. However, they are also the most expensive type of pigment.
Difference between organic and inorganic pigment
|
Criteria |
Organic |
Inorganic |
|
1. Brilliancy |
Good |
Less good. |
|
2. Covering power |
Less |
Good |
|
3. Bleeding tendency |
Tendency to cause bleeding |
No bleeding |
|
4. Settling |
Less |
More settling due to high density |
|
5. Body |
Less |
Good |
|
6. Lightfastness |
Less |
Good |
|
7. Purity |
Available in the purest form |
It May contain impurities if made out of the earth colors |
Objects of pigments/Role of pigment
1. To provide color.
2. To obliterate the surface.
3. To increase the resistance of the surface to light.
4. To increase the resistance to corrosion.
5. To modify flow properties.
6. To improve the weathering properties and durability.
7. To improve the strength of the surface.
Properties of pigment
Fastness: Pigments must be fast to light, heat, smoke, dust, different gases present in the atmosphere, dilute acids and alkalis, rainwater & different common organic solvents.
Abrasion: The particle of a good pigment must show a high degree of resistance to abrasion.
Crystallization: If a pigment crystallizes out when present in dilute paint emulsion, it must be discarded as a pigment. The character of a crystal is quite different from its ground particles, so crystallization is a severe defect to pigment.
Refractive indices:
The covering power of the pigment also depends upon its optical density, which its refractive index can represent. The higher the refractive index, the higher is the covering power. Since the refractive indices of inorganic pigments are very high compared to organic pigments, the covering power of inorganic pigments is always superior to organic pigments, even though the particle size is more significant.
Nature of surface: The surface of pigment particles should be such that it can quickly reflect those light waves that represent the pigment's color. When the surface of the pigment particles becomes hash, its brilliancy is vastly reduced.
Particle size: Smaller the particle size, the higher the covering power. The particle size of commercial pigments forms fine colloidal particles to relatively coarse particles. The particle size of all pigments cannot be reduced to the same extent, even with the best available grinding types of equipment. The covering powers of inorganic pigments are generally higher than organic pigments though the particle size is more extensive.
Pigment Applications:
Pigments can be used in various applications, such as paints, inks, plastics, and textiles. They are also used in food coloring and cosmetics.
Organic pigments are made from carbon-containing materials. They are generally more expensive than inorganic pigments, but they have better colorfastness properties.
Inorganic pigments are made from noncarbon materials. They are generally less expensive than organic pigments.
Choosing the Right Pigment:
When choosing a pigment, it is essential to consider the application requirements. For example, if colorfastness is a requirement, the organic pigment may be the best choice.
Pigments are often added to substances for coloration purposes. Pigment colors are known as dyes or dyestuffs. Pigments are also used in industrial applications such as paints and plastics production due to their durability. Additionally, they can naturally occur on plants, animals, and rocks. Pigments are also used in foods to create coloration effects on the product.
Pigment Colors:
Pigment colors can be divided into three groups. A single pigment can have multiple names depending on where it is produced or its chemical composition. For example, iron oxide is a common ingredient in the paint with different names depending on the country. The three groups of pigment colors are organic, inorganic, and metal. Pigment manufacturers create colors by blending different pigments to achieve the desired color. Organic pigments are made from carbon-containing materials; inorganic pigments are made from noncarbon materials; metal pigments are made from metal compounds. Pigments are used in paints, plastics and textiles. Pigment colors can be divided into three groups - organic pigments are made from carbon-containing materials; inorganic pigments are made from noncarbon materials; metal pigments are made from metal compounds. The three primary colors of pigment are red, yellow, and blue.
- Pigments are used in various applications, such as paints, inks, plastics and textiles.
- Pigments can be found naturally occurring on plants, animals or rocks.
Pigment Example
Pigments may be natural (such as ochre) or artificial (titanium dioxide). There is also white pigment made from all the primaries put together in equal parts.
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