Paint is a colloid, which is a heterogeneous combination in which one component is disseminated in another. The components of paint include pigment(s), binder(s), and possibly other additives.
Pigment is the term given to any colorant used in painting. The most common pigments are red, yellow, blue, white, and black. Some pigments are natural, such as clay or stone dust, others are manufactured, such as titanium dioxide or zinc oxide.
The binder that holds the pigment to the canvas or some other support material is called a vehicle. There are two main types of vehicles: organic and inorganic. Organic binders include oils and resins that dry to form a protective coat over the painted surface. Inorganic binders include glues such as urethane resins and acrylics. Glues are used instead of oil or resin for flexibility when making large paintings.
Other additives included in paint to improve its performance include driers, lightfastness agents, and colorants. Drying agents are substances that control the speed at which water evaporates from a wet paint layer. This allows the painter to work for longer periods of time without returning to a warm studio or gallery space.
Solvents in paints dissolve or disperse various components employed in the paint formulation (such as pigment and resin), resulting in the appropriate application consistency. When paint is applied, the solvent evaporates, allowing resin and pigment to form a paint film (a coat) that dries quickly. The type of solvent used affects the drying time required for a given thickness of paint.
The most common paint solvents are hydrocarbons, alcohols, ethers, ketones, and esters. They can be either volatile or non-volatile. Volatile solvents evaporate rapidly with air movement, while non-volatile solvents must be removed by heat or pressure to reduce their concentration in the paint.
Hydrocarbon solvents include gasoline, kerosene, diesel fuel, heating oil, and lubricating oil. They are high-molecular-weight compounds composed of carbon and hydrogen atoms bound together in varying degrees of separation. The simplest hydrocarbon is methane, which consists of one carbon atom bonded to four hydrogen atoms. Each additional bond adds another unit to the molecule. Hydrocarbons contain a number of reactive sites where chemical reactions can occur, and thus are useful in altering the properties of a variety of materials. For example, methyl methacrylate is formed when methane molecules attach to acrylic acid molecules.
Alcohols are composed of hydrogen and oxygen atoms bonded together with single bonds.
Paint is made up of binders, pigments and fillers, solvents or water, and additions. The raw ingredients used in the development of new paint are chosen for their compatibility with the item to be painted. Depending on the type of paint, the mixing ratio varies. For example, oil paints contain linseed (or flax) oil as a binder and pigment, while acrylic paints use polymers as a binder and pigment.
The three main types of paint are water-based, oil-based, and latex-based. Each type has its advantages and disadvantages, which will be discussed further below.
Water-based paints are made from oils or alkyd resins that have been modified so that they can be mixed with water instead of alcohol or other organic solvents. These paints are easy to wash off of nonporous surfaces such as wood, but they can soak into porous surfaces such as plaster or cement. They also tend to fade when exposed to sunlight over time.
Oil-based paints consist of natural or synthetic oils that have been combined with a drying agent such as linseed oil or walnut oil. These paints are very durable and don't smear easily, but they may stain clothing or other items that come in contact with them. They also require more care and maintenance than water-based paints because they are not water-soluble.
In general, house and interior paints are inhomogeneous mixes. This means that they are not single substances but rather consist of two or more different materials that are mixed together to create one product. These materials include a pigment to give the paint its color and a binder which is used to hold the pigment together. In addition, there may be additives such as moisture-resistant agents, flame retardants, and plasticizers.
Paints can be classified as either water-based or oil-based. Water-based paints contain emulsified polymers that act as binders for the pigment particles. Oil-based paints use petroleum products such as mineral spirits as solvents for the pigments. Latex paints are hybrid mixtures of natural rubber proteins and synthetic resins. They are usually transparent when first made but will eventually darken due to exposure to light and air.
The exact composition of latex paints varies depending on the brand but generally includes styrene monomer, acrylic monomers, vinyl acetate, and aluminum sulfate. The main purpose of adding these other ingredients to latex is to help the polymerization process by acting as catalysts or "brains" that help molecules join together into longer chains.