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Components There are several primary components to a paint: binder, pigment, filler, diluent, and additives. However, only the binder is absolutely required. The binder is the part which eventually solidifies to form the dried paint film. Pigments give a color to a paint. Pigments may also have the same functions as fillers: increase the thickness and hardness of the film and adjust the coloring power and opacity. The diluent serves to adjust the viscosity of the paint. It is volatile and does not become part of the paint film. There are various additives, which components that are added in small amounts to improve some property, such as color opacity and matness, pigment dispersion, or stability. Typical binders include synthetic or natural resins such as acrylics, polyurethanes, polyesters, melamines, epoxy, or oils. Binders can be categorized into three sorts: those that dry, those that cure when they dry, and those that do not depend on drying for curing. Paints that dry contain a solid binder dissolved in a solvent; this forms a solid film when the solvent evaporates, and the film can dissolve in the solvent again. Latex paints, for example, cure irreversibly when they dry, since they undergo polymerization into irreversibly bound networked structures, so that the paint will not redissolve in the solvent. Recent environmental protection requirements discourage the use of evaporating solvents (VOCs), and alternative means of curing have been developed, particularly for industrial purposes. Epoxy coating, for example, is applied by mixing paint and hardener, which cure by forming a hard plastic structure. Such paints do not, strictly speaking, "dry" at all, but harden. In UV curing paints, the solvent is evaporated first, and hardening is then initiated by ultraviolet light. Typical diluents include organic solvents such as petroleum distillate, alcohols, ketones, esters, glycol ethers, and the like. Water is a common diluent. Sometimes volatile low-molecular weight synthetic resins also serve as diluents. Fillers serve to thicken the film, support its structure and simply increase the volume of the paint. Not all paints include fillers. Pigments that also function as fillers are called simply "pigments"; "fillers" are generally color-neutral and opaque. It is necessary to adjust the resulting off-white color with pigments to give the desired color. Common fillers are cheap and inert, such as talc, lime, baryte, clay, etc. Depending on the paint, most of the paint film may consist of pigment/filler and binder, the rest being additives. Typical additives include pigments, dyes, catalysts, thickeners, stabilizers, emulsifiers, texturizers, adhesion promoters, flatteners (de-glossing agents), and the like. After application, the paint solidifies and becomes tack-free. Depending on the type of binder, this hardening may be a result of curing (polymerization), evaporation, or even cooling. In oil-based paint, curing takes the form of oxidation, for example oxidation of linseed oil to form linoxin to create a varnish. Other common cured films are prepared from crosslinkers, such as polyurethane or melamine resins, reacted with acrylic polyester or polyurethane resins, often in the presence of a catalyst which serves to make the curing reaction proceed more quickly or under milder conditions. These cured-film paints can be either solvent-borne or waterborne. Latex paint is a water-based emulsion of solid monomers. The term "latex" in the context of paint simply means a water emulsion; latex rubber (the sap of the rubber tree that has historically been called latex) is not an ingredient. When the water evaporates, the monomer undergoes emulsion polymerization to form a solid film. The polymer itself resists water (and typically some other solvents). Residual surfactants in the paint as well as hydrolytic effects with some polymers cause the paint to remain susceptible to softening and, over time, degradation by water. Still other films are formed by cooling of the binder. For example, encaustic or wax paints are liquid when warm, and harden upon cooling. Art Main article: Painting 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 century, water-based paints, including watercolors and acrylic paints, became very popular with the development of acrylic and other latex paints. Milk paints (also called casein), where the medium is derived from the natural emulsion that is milk, were popular in the 19th century and are still available today. Egg tempera (where the medium is an emulsion of egg yolk mixed with oil) is still in use as well, as are encaustic wax-based paints. Gouache is a variety of watercolor paint which was also used in the Middle Ages and Renaissance for manuscript illumination. The pigment was often made from ground semiprecious stones such as lapis lazuli and the binder made from either gum arabic or egg white. Gouache is commercially available today. Poster paint has been used primarily in the creation of student works, or by children. Pigment The proper name for the effects of "prism paint," a made up name, is "interference." Main article: Pigment Pigments, usually insoluble powders, are used both to provide color, and to make paint opaque, thus protecting the substrate from the harmful effects of ultraviolet light while also increasing a paint's hiding power. Some pigments are toxic, such as those used in lead paint. Paint manufacturers replaced lead white with a less toxic substitute, which can even be used to color food titanium white (titanium dioxide) which was first used in paints in the 19th century. The titanium white used in most paints today is often coated with silicon or aluminum oxides for better durability. Some newer paints—called prism paint—can produce effects where the color changes depending on the angle (orientation) at which it is viewed. Modern U.S. and Canadian banknotes, specifically the newer higher denomination notes, have this effect on them. This effect is produced by having pigment molecules that are long and thin and are meant to dry in a specific orientation, with different ends of the molecule being different colors. Application Paint can be applied as a solid, a gaseous suspension (aerosol) or a liquid. Techniques vary depending on the practical or artistic results desired. As a solid (usually in industrial and automotive applications), the paint is applied as a very fine powder, then baked at high temperature. This melts the powder and causes it to adhere (stick) to the surface. The reasons for doing this involve the chemistries of the paint, the surface itself, and perhaps even the chemistry of the substrate (the overall object being painted). As a gas or as a gaseous suspension, the paint is suspended in solid or liquid form in a gas that is sprayed on an object. The paint sticks to the object. The reasons for doing this include: In the liquid application, paint can be applied by direct application using brushes, paint rollers, blades, other instruments, or body parts. Examples of body parts include fingerpainting, where the paint is applied by hand, whole-body painting (popular in the 1960s avant-garde movement), and cave painting, in which a pigment (usually finely-ground charcoal) is held in the mouth and spat at a wall (Note: some paints are toxic and might cause death or permanent injury). Rollers generally have a handle that allows for different lengths of poles which can be attached to allow for painting at different heights. Generally, roller application takes two coats for even color. A roller with a thicker nap is used to apply paint on uneven surfaces. Edges are often finished with an angled brush. After liquid paint is applied, there is an interval during which it can be blended with additional painted regions (at the "wet edge") called "open time." The open time of an oil or alkyd-based emulsion paint can be extended by adding white spirit, similar glycols such as Dowanol™ (propylene glycol ether) or commercial open time prolongers. This can also facilitate the mixing of different wet paint layers for aesthetic effect. Latex and acrylic emulsions require the use of drying retardants suitable for water-based coatings. Paint may also be applied by flipping the paint, dripping, or by dipping an object in paint. Interior/exterior house paint tends to separate when stored, the heavier components settling to the bottom. It should be mixed before use, with a flat wooden stick or a paint mixing accessory; pouring it back and forth between two containers is also an effective manual mixing method. Paint stores have machines for mixing the paint by shaking it vigorously in the can for a few minutes. Water-based paints tend to be the safest, and easiest to clean up after using -- the brushes and rollers can be cleaned with soap and water. It is difficult to reseal the paint container and store the paint well for a long period of time. Store upside down, for a good seal, in a cool dry place. Protect from freezing. Proper disposal of paint is a challenge. Avoid acquiring excess paint. Look for suitable recycled paint before buying more. Try to find recycled uses for your left over paint. Paints of similar chemistry can be mixed to make a larger amount of a uniform color. Old paint may be usable for a primer coat or an intermediate coat. If you must dispose of paint, small quantities of water based paint can be carefully dried by leaving the lid off until it solidifies, and then disposing with normal trash. But oil based paint should be treated as hazardous waste, and disposed of according to local regulations. Product variants History Cave paintings drawn with red and yellow ochre, hematite, manganese oxide and charcoal may have been made by early homo sapiens as long as 40,000 years ago. Ancient painted walls, to be seen at Dendera, 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: 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. Paint was made with the yolk of eggs and therefore, the substance would harden and stick onto the surface applied. See also | ||||||||||
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