There are generally three parts to a paint, a solid part, and two liquid parts. Combined, the two liquid parts make up the medium or vehicle. The solid part is mostly pigments, which are particles that provide color and also help make the paint opaque. The binder (usually a natural or synthetic resin) is that part of the vehicle which eventually solidifies to form part the dried paint film. The solvent or diluent (often an organic solvent, or water) is that part of the vehicle that is volatile and does not become part of the paint film. The major function of the solvent is to thin the paint to make it easy to apply.
After application, the liquid paint solidifies, leaving the binder and pigment as a colored coating. Depending on the type of binder, this hardening may be a result of processes such as curing (in oil paint, this takes the form of oxidation of linseed oil to form linoxin), evaporation (most water-based paints are emulsions of solid binders in water; when the diluent evaporates, the molecules of the binder coalesce to form a solid film), cooling (encaustic, or wax, paints are liquid when warm, and harden upon cooling), etc.
Since the time of the renaissance, siccative (drying) oil paints, primarily linseed oil, have been the most commonly used kind of paints in fine art applications; oil paint is still common today. However, in the 20th centry, water-based paints, including watercolors and acrylic paints, became very popular with the development of latex and acrylic pigment suspensions. Milk paints (also called casein), where the medium is derived from milk, were popular in the 19th century and are still available today. Egg tempera (where the medium is egg yolk) is still in use as well, as are encaustic wax-based paints.
Lead paint: White pigment does not add color, but serves the very important function of increasing opacity and making the paint resistant to UV radiation. For centuries, the primary white pigment in paints was white lead (also called lead white), one of the oldest pigments known. The problem with white lead is that it is extremely toxic. See lead.
It wasn't until the middle of the 20th century that white lead was generally replaced by a less toxic substitute, titanium white, which was first used in paints in the 19th century. The titanium white used in most paints today is actually a mixture of titanium dioxide (pure titanium white) and zinc oxide (zinc white). See pigment.
Historical notes from Household Cyclopedia:
Ancient painted walls, to be seen at Dendara, Egypt, although exposed for many ages to the open air, still possess a perfect brilliancy of color, as vivid as when painted, perhaps 2000 years ago. The Egyptians mixed their colors with some gummy substance, and applied them detached from each other without any blending or mixture. They appeared to have used six colors, viz., white, black, blue, red, yellow, and green. They first covered the field entirely with white, upon which they traced the design in black, leaving out the lights of the ground color. They used minium for red, and generally of a dark tinge.
Pliny mentions some painted ceilings in his day in the town of Ardea, which had been executed at a date prior to the foundation of Rome. He expresses great surprise and admiration at their freshness, after the lapse of so many centuries.
Microsoft Paint is an electronic drawing and painting program.