A Guide to Pigment Composition, Characteristics and Uses
Pigments are what add color to materials like paints, cosmetics, textiles, art, and more. The first pigments date back to 40,000 years ago, and today, almost every industry uses pigments in its manufacturing processes.
Pigments differ in opacity, thermal stability, color, chemical resistance, and more. They can be natural, synthetic, or a combination of the two.
What Is a Pigment?
A pigment is a set of compounds with intense color. Pigments are entirely or almost insoluble in water and reflect light. A pigment changes the color of reflected or transmitted light due to selective wavelength absorption.
History of Pigments in Color Production
The first color palettes were made of pigments from natural materials like charcoal, burnt animal fats, chalk, and ochre. They consisted of five colors: yellow, brown, black, white, and red. The early man used pigments for body decorations and on cave walls.
Egyptians and the Chinese discovered more pigments from minerals like azurite, copper, and malachite.
In 3000 BC, Egyptians created the first synthetic pigment, Egyptian blue. The greenish-blue pigment consists of sand, copper ore, and lime. Paleolithic artists also contributed to the discovery of pigments.
Types of Pigments
While all pigments add color to a material, they’re not all the same.
1. Synthetic Pigments
Manufacturers make synthetic pigments from petrochemicals through simple chemical reactions like oxidation. They may use iron, lead, and other metals in their formulations. These pigments don’t contain carbon links or chains.
The particle size of synthetic pigments is bigger than that of organic compounds, so they reflect more light. As a result, inorganic pigments are more opaque and insoluble than their organic counterparts. Synthetic pigments include titanium dioxide, chromium, and cadmium pigments.
2. Natural Pigments
Natural or organic pigments contain carbon chains. Manufacturers derive them from plants, animals, and minerals. Manufacturing organic pigments involves washing, drying, crushing, and mixing.
Although they have less color intensity, natural pigments are less toxic than inorganic pigments. Some manufacturers combine them with chemicals to make synthetic organic pigments. These include azo-pigments, diazo-pigments, acid-dye pigments, alizarin, phthalocyanine, and quinacridone.
3. Metallic Pigments
Metallic pigments are naturally occurring and tend to be dry. They consist of metals and mineral ores like aluminum, zinc, and copper. Manufacturers process them through pulverization and mixing.
Metallic pigments are common in automotive coatings and some cosmetic products.
4. Industrial Pigments
Industrial pigments are organic or inorganic pigments in powder form. They’re mixed with resins or paints to provide color, durability, and corrosion resistance. Industrial pigments are also available in other forms, including liquids, granules, waxes, pellets, and chips.
Industrial pigments are colorants for beverages, food, paper, plastics, and pharmaceuticals.
The Role of Pigments in Color Production
Dry powder pigments combine with a binder to form a color used in manufacturing processes.
Fine Art
Paints consist of pigment and binders. The pigments differ in color fastness, drying time, and color intensity. Binders hold pigments together and form a film on the applied surface.
Artists use pigments in monochromatic colors for abstract painting. It creates harmony and balance. Artists also blend pigments to create different hues. For instance, mixing yellow and blue pigments yields the color green.
Industrial Applications
In the textile industry, pigments dye synthetic and natural fibers. They’re spun into yarn in pellet form, known as solution dyeing. Solution dying is more sustainable than traditional dyeing, which uses energy, chemicals, and water.
Other industrial applications include the coloration of soap, plastics, paper, wood, metal, and more.
Cosmetic Products
The cosmetic industry uses pigments to make personal care products like soaps and body creams. Organic pigments containing azo colorants, lakes, and botanicals are common in cosmetic formulations. While some azo pigments and lakes are harmful to the skin, botanicals are safe and non-toxic.
Top Considerations When Choosing a Pigment
Opacity
Pigments with higher color strength are more opaque. Inorganic pigments have high opacity, unlike organic pigments.
Materials with organic pigments allow light to pass through. Organic pigments are suitable for glasses, while inorganics are effective for paints and coatings.
Thermal Stability
Organic and inorganic pigments resist fading and damage when exposed to high temperatures. But, inorganic pigments have better thermal stability in extreme sunlight and heat.
Chemical Resistance
Pigments need chemical inertness to resist degradation with exposure to chemicals. You can find inert pigments in paints, coatings, cable insulation, and ink. While organic pigments have high chemical resistance, the resistance level varies in inorganic pigments.
Tinting Strength
Organic pigments have a higher tinting strength than their inorganic counterparts. With such pigments, you need small amounts for coloring materials. This quality makes organic pigments the standard colorant for plastics and resins.
Dispersion
Since pigments come in solid forms, they need wetting to make them applicable on surfaces. Dispersing them in liquid mediums ensures stability and prevents re-agglomeration.
Toxicity
Inorganic pigments containing lead, cadmium, cobalt, and manganese are toxic. Such pigments are unsafe for inhalation and cause allergic reactions on the skin. Some metal pigments are also carcinogenic and not approved for use. Check for FDA-certified pigments in food, cosmetics, and drugs.
Lightfastness
Inorganic pigments have a high resistance to fading with exposure to light. High-performance organic pigments are also lightfast, which varies with every type.
Color
Pigments are available in a wide variety of hues. While organic pigments are brighter, they’re less durable than inorganic types. Inorganic pigments are known for their excellent hiding power and durability.
Solubility
Since pigments are insoluble, a liquid medium (vehicle) is used to make them disperse. Examples of pigment vehicles include linseed oil, alcohol, glycol ethers, and more. For water-based or latex paints, water serves as the vehicle.
Health and Safety Considerations for Pigments
Use personal protective equipment when handling any pigments. Exposure to dry pigments poses a risk of inhaling metal contaminants and chemicals. Most metal pigments are carcinogenic and pose health risks when they penetrate the lungs.
Check the Material Safety Data Sheet (MSDS) for pigment identification and safe handling instructions. When mixing dry pigments, use a fume hood to avoid inhaling the pigment dust.