Defining Pigments and Dyes
Pigments and dyes are both substances used to impart color, but they differ fundamentally in their chemical and physical properties. A pigment is a finely ground, insoluble solid that remains suspended in a medium, forming a coating or film on the surface. In contrast, a dye is typically a soluble substance that chemically bonds with or is absorbed into the substrate it colors, becoming an integral part of the material itself.
How They Impart Color
The mechanism by which they color objects is a key distinction. Pigments provide color by selectively absorbing and scattering light particles (photons) when applied as a coating. Because they are insoluble, they rely on a binder to adhere to a surface. Dyes, however, dissolve in a solvent (like water or alcohol) and color by chemically reacting with or being physically absorbed into the material's molecular structure, thus coloring the entire substance rather than just coating it.
Practical Examples of Use
Common examples illustrate their roles. Pigments are found in paints, inks, plastics, and cosmetics, where they provide opacity, lightfastness, and durability by sitting on the surface. For instance, titanium dioxide is a widely used white pigment. Dyes are prevalent in textiles, food coloring, and some types of inks, such as those used in inkjet printers, where they offer vibrant, translucent colors that penetrate the material deeply, like indigo dye in denim.
Key Properties and Applications
Beyond solubility, pigments generally offer superior lightfastness (resistance to fading from light exposure), weather resistance, and opacity compared to dyes. This makes them ideal for outdoor applications and protective coatings. Dyes, while often less durable to light and weathering, can produce more brilliant and uniform colors, especially when coloring fibers, and can achieve transparent effects not possible with pigments due to their penetrative nature.