How Spray Paint Works

Those ubiquitous, cylindrical cans you have sitting around the garage represent a pretty simple design. They're usually constructed from light gauge steel or aluminum and include a valve, a dip tube and a pea, each of which we'll discuss later in this section.

Spray paint works the way it does because it's actually a combination of paint and a gas propellant. During the manufacturing process, the cans are first filled with paint and then injected with the gas propellant. The valve is then crimped, trapping the highly compressed compound within the confines of the can. And this is the genius behind spray paint's efficiency. Chlorofluorocarbons were the propellant of choice for most aerosol-delivered products, including spray paint, until 1978, when it was banned after it was discovered that it contributed to the depletion of the ozone layer [source: Martineau]. So the industry turned to hydrocarbons – organic compounds made up of hydrogen and carbon – as an alternative until the 1980s when it was determined they may cause smog (butane, propane and methane are a few common examples of hydrocarbons) [source: Practice Greenhealth]. Today, most aerosols use hydrofluorocarbons ,which consist of hydrogen, fluorine and carbon, and present a much smaller risk to the environment because they do not contain potentially harmful elements like chlorine.

So, how does all of this work together?

When the nozzle is pressed, the paint-propellant mixture rushes up the dip tube in response to the sudden, dramatic change in pressure that causes the propellant in the can to expand, forcing the paint through the tube and out through the nozzle. The dip tube acts like a straw, with one end attached to the valve and the other end near the bottom of the can. Once through the dip tube, the nozzle and free of the pressurized can, the propellant expands and the paint atomizes into a fine, even mist. These tiny paint particles (not actually atoms) are evenly distributed because they are positively charged, repelling each other as they leave the can. And because the object being painted is oppositely charged, spray paint adheres to the surface and can be applied in even, smooth layers with almost zero waste.

The pea, a small metal ball bearing, maintains the propellant-paint mixture inside the can. By shaking the can, the pea agitates the mixture so you can be sure the two components are combined properly. This is where spray paint gets its signature rattle. If the paint and propellant are allowed to settle, they will come out in uneven proportions, causing the paint to clump.

This combination of mechanics, chemistry and physics has turned spray paint into one of the most useful tools for home improvement. But the benefits are not limited to household use, so keep reading and discover some heavy-duty applications of spray paint.

The benefits spray paint offers weekend warriors -- fast application, even coating, little waste -- are magnified in a large-scale setting, and it wasn't long after Seymour launched his idea to the masses that factories and manufacturing plants started to take notice.

Powder coating, vacuum coating and flatline spraying are the three most common methods for industrial spray painting.

Powder coating, sometimes referred to as electrostatic spray painting, is a method for applying dry paint to a surface. Like the paint-propellant mixture inside a spray can, compressed air is used to drive atomized particles of paint through a spray gun onto the target. These particles are very fine and resemble dust, or a powder. And just as with the aerosol can, the particles acquire an electrical charge from the friction created as they pass through the spray nozzle. Because positively charged particles repel each other, they distribute themselves evenly before they make contact with the object being painted. Since the object is always oppositely charged, usually by being grounded using a cable attached to any metal part of the assembly, the paint adheres to the surface.

Companies turn to vacuum coating to apply water-based paint to objects (usually pieces manufactured in sheets such as wood, glass or plastics) that require extremely thin coats. In this method, the object being painted is placed into a chamber, or paint reservoir, where its entire surface area is either submerged into a paint solution or sprayed with a nozzle. The paint is applied in the same volume uniformly around the object, so the entire piece is covered. Finally, the object is removed from the chamber and exposed to extremely high levels of UV light. This photochemical process, called UV curing, uses light rather than heat and is capable of drying objects in seconds.

Finally, flatline spraying is among the most popular methods for painting material that's manufactured in large quantities. Objects, usually small items less than 4 inches (about 10 centimeters) thick, on an assembly line are fed into a machine designed specifically for that part. The paint is applied by spray guns programmed to complete a series of movements to ensure the entire piece is covered.

But spray paint isn't all home improvement and manufacturing. Keep reading to find out how spray paint is making women and decaying buildings more attractive.

Spray painting has also turned the worlds of tanning, cosmetics and pop culture upside down. Sunless tanning has been popular for years since ultraviolet radiation from the sun and tanning beds have been linked to cancer. Salons offering spray-on tanning options use methods similar to manufacturers. A would-be sun worshipper steps into a small booth and sprayers, either hand-held or fixed, use compressed air to apply a chemical solution to the customer's skin.

It isn't paint that causes the skin to turn brown, but a sugar called dihydroxyacetone (DHA). When DHA touches dead skin, a reaction takes place that causes the skin to brown temporarily (usually for about a week).

Makeup artists have adopted airbrushes, small air-powered tools, for personal application of cosmetics. Airbrushes use compressed air to atomize liquid makeup, much the way the propellant in a can of spray paint atomizes the paint it's mixed with. The result is a thin, evenly distributed layer of makeup that's much smoother than can be applied with a powder brush. The rise of high-definition television, where unforgiving cameras reveal every flaw, has contributed to the popularity of this method of make-up application.

Probably most noticeably, graffiti artists have embraced the convenience of spray paint as their medium of choice. In the 1960s and '70s this form of expression exploded in Philadelphia and New York City as artists began creating colorful, thematic murals in public places -- most notably on subway cars -- as a way to generate buzz for their other artistic endeavors [source: Scape]. Since most street artists operate outside the law, the light and portable nature of spray cans makes them an ideal tool. And spray paint offers a variety of bright colors, adheres well to virtually any surface and provides good coverage in a short time.

Graffiti, once a symbol of lawlessness, has evolved into a chic art form complete with gallery showings, high-dollar pieces, and even tortured artists like the celebrated Jean-Michel Basquiat, whose work has been shown in museums around the world [source: Davies]. Even spray paint companies are helping elevate street art into the mainstream by donating product for legal, large-scale projects [source: Laboy].

From its beginnings as a way to get a paint job done faster, to using it to mask imperfections or make an artistic statement, spray paint has left an indelible mark on global pop culture.