Paint is a substance that colors and protects a wide variety of surfaces. It is used on the inside and outside walls of buildings, on automobiles, on furniture and household appliances, and on many machines and machine parts. Most paints go on as liquids and then dry to form a thin solid film. A typical coat of paint is about 3/1,000 inch (0.08 millimeter) thick.
Paint consists of one or more finely ground pigments and a liquid vehicle. Pigments determine the color of the paint and provide it with certain other properties. Pigments commonly used for their color include titanium dioxide (white), iron oxide (yellow or red), phthalocyanine (blue or green), and toluidine (bright red). Manufacturers often add clay, mica, and talc to paint to increase its resistance to wear. These semitransparent materials are called extenders or inert pigments. Such pigments as zinc phosphate and barium metaborate help paint protect metal surfaces against rust. Pigments composed of fine metal powders give surfaces a metallic finish.
A paint's vehicle carries the pigment and binds it to a surface. Paint vehicles are composed of one or more resins and a solvent. Resins are sticky substances obtained from plants or manufactured through chemical processes. They are the main ingredient in paint. People often refer to paints by their resin type. Resins include acrylics, alkyds, epoxies, and polyurethanes. Resins largely determine the adhesive quality, drying time, gloss, and hardness of paints. Most are nearly colorless.
The solvent is the ingredient that makes paint a liquid. The solvent depends on the resins used. Most household paints, and an increasing number of industrial paints, use water as a solvent. Other commonly used solvents include mineral spirits, ketones, glycol ethers, and xylene. Solvents are sometimes called paint thinners. Vapors given off by some solvents can threaten a user's health, contribute to air pollution, and even play a part in the thinning of the protective layer of ozone in the upper atmosphere. The governments of many countries regulate the use of solvents in paints.
