What is the Difference Between Dye and Pigment

The main difference between dye and pigment is that dye molecules are very small whereas pigments are much larger. Therefore, dyes easily dissolve in water and many solvents while pigments do not dissolve in water. 

Dye and pigment are two types of compounds which can impart a color to a material. Furthermore, dyes have a direct affinity to textiles while pigments have no direct affinity to textiles. Therefore, dyes diffuse in the fabric while the pigments diffuse on the fabric.

Key Areas Covered

1. What is a Dye
     – Definition, Characteristics, Importance
2. What is a Pigment
     – Definition, Characteristics, Importance
3. What are the Similarities Between Dye and Pigment
     – Outline of Common Features
4. What is the Difference Between Dye and Pigment
     – Comparison of Key Differences

Key Terms

Auxochromes, Binder, Dye, Lightfastness, Pigment, Size, Solubility

What is a Dye

A dye is a type of small soluble colorant. Here, solubility means that the dye dissolves well in the binder or the application fluid, which can be water. Also, dyes are more transparent, allowing it to glaze over the material. Generally, dye molecules have elements which help to bind to the surface. These elements form either van der Waal’s forces, hydrogen bonds or even ionic bonds based on the characteristics of the substrate.

Figure 1: Textile Dyes

Furthermore, the part of the dye molecule responsible for the production of the color is known as the chromophore. Most dyes contain auxochromes, which are either basic or weakly acidic groups, increasing the color of the dye. Some dyes used in the textile industry are acid dyes, basic dyes, direct dyes, azoic dyes, sulfur dyes, etc.

What is a Pigment

A pigment is an insoluble material ground into a fine powder used as a colorant. Here, as they are insoluble, pigments are suspended in the binder. Therefore, the binder is responsible for holding pigments in place on the material. Another two characteristic features of pigments are their opacity and low tinting strength. As they are opaque, pigments can completely cover color on the material. Here, the tinting strength refers to how well two colors mix with each other, fading their colors to each other.

Figure 2: Pigment Dyes

Furthermore, most of the pigments are inorganic metals such as titanium, cadmium, lead, etc. Usually, pigments are mainly used to produce inks, paints, plastics, and other polymeric materials. Significantly, the lightfastness is high in pigments, which refers to the resistance of a colorant to fading it is when exposed to light.

Similarities Between Dye and Pigment

• Dye and pigment are two types of compounds which can give a color to a material.
• Therefore, they are known as colorants.
• Also, both can be either natural or synthetic.
• They have various applications in the textile industry, printing, painting, candle making, etc.

Difference Between Dye and Pigment

Definition

A dye refers to an intensely colored or fluorescent organic substance, which imparts color to a substrate by selective absorption of light while a pigment refers to the colored, black, white or fluorescent particulate organic or inorganic solids, usually insoluble in, and essentially physically and chemically unaffected by, the vehicle or substrate in which they are incorporated. Thus, this is the main difference between dye and pigment.

Size

A dye particle is very small while a pigment is comparatively large.

Transparency

Transparency is another difference between dye and pigment. Dyes are more transparent while pigments are comparatively less transparent.

Solubility

Solubility is also a difference between dye and pigment. Dyes are soluble in water while pigments are not soluble in water and many solvents.

Type of Compounds

Most dyes are organic while pigments can be either organic or inorganic.

Auxochrome Groups

Auxochrome groups can be present in dyes while no auxochrome groups are present in pigments.

Availability

Also, one other difference between dye and pigment is that dyes are available in a large number while pigments are less available.

Affinity

Moreover, dyes have a direct affinity to the material while pigments have no direct affinity to the material.

Binding Agents

Dyes do not require binding agents while pigments require binding agents. Hence, this is another difference between dye and pigment.

Change in the Structure during Application Process

The structure of dyes temporary alters during the application process while the structure of pigments does not alter during the application process.   

Diffusion

Furthermore, dyes diffuse in the fabric while pigments diffuse on the fabric.

Method of Imparting Colors

Dyes impart colors by the selective absorption while pigments impart colors by scattering of light or by selective absorption.

Cost

Their cost is another major difference between dye and pigment. Dyes are costly while pigments are cheap.

Lightfastness

Dyes have low lightfastness while pigments have high lightfastness.

Product Resistance

The product resistance of dyes is lower while the product resistance of pigments is higher.

Combustive Properties for Candle Making

Dyes are compatible with burning while pigments tend to clog the wick during burning.

Longevity Factor

Additionally, dyes do not last long while pigments last longer.

Types of Materials

Dyes are compatible with a wide range of materials while suitable materials for pigments are limited.

Conclusion

A dye is a type of colorant molecule used to give a color to a material. Generally, dyes are fine particles that are mostly soluble. They are available in large number. On the other hand, pigments are comparatively large compounds, which are insoluble. However, pigments last longer than dyes. Therefore, the main difference between dye and pigment is their size and durability.

References:

1. “Definitions of a Dye and a Pigment.” Society of Dyers and Colourists & AATCC, Spotlight Studios, Available Here.

Image Courtesy:

1. “Textile dyes” By Ahom04 – Own work (CC BY-SA 4.0) via Commons Wikimedia  
2. “Indian pigments” By Dan Brady (CC BY 2.0) via Commons Wikimedia  

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