The Removal of Oxidation or Old Wax on Cars
Automotive paint is a strange sort of contradiction; as someone once quipped, it's strange that manufacturers made cars out of something...
Automotive paint is a strange sort of contradiction; as someone once quipped, it's strange that manufacturers made cars out of something as sturdy as metal and then covered them with something so fragile that people fuss over the slightest scratch. If you're the type of person who actually cares about how this fragile coating looks, then old wax and paint oxidation can really ruin your day. Fortunately, you don't have to look far to find a plethora of products specifically engineered to bring old paint back to something resembling factory-fresh.
Contamination and Aging
Paint damage comes in two basic varieties: mechanical and chemical. Mechanical damage includes scratches or abrasions, as well as foreign object embedding in the paint surface. Chemical damage can involve damage via solvents, bug splatter, bird poo, acid rain or molecular breakdown from exposure to the sun. Ultraviolet radiation breaks the paint's polymer chains apart, eventually bleaching it and turning the surface a chalky white.
Clay Bars
Clay bars, be they natural or synthetic, are a somewhat recent innovation. Clay is a bit sticky to the touch, but is far more so on a molecular and microscopic level. Spraying a car with specialized clay bar lubricant and rubbing it with a clay bar causes contaminants like metal, sand and old wax to come out of the paint and stick into the softer clay instead. Clay-barring a car's paint is now considered a de rigueur step before any quality polish job. Polishing a car's paint before clay-barring it may only move the embedded contaminants around, thus damaging the paint further.
Polishing
Don't cut corners when it comes to polish. Polish is essentially sandpaper in liquid or paste form, and can do some serious damage to your cars paint if applied carelessly. Name-brand polishes utilize consistently-sized, quality abrasives that will minimize the risk of burning through the paint's clear coat. This isn't as much of a concern if you're hand polishing, but is a very real possibility if you're using an electric polishing machine. Old wax should come of using a clay bar, and a fairly mild polish and polishing pad should take care of surface oxidation.
After Treatment
Waxing is crucial after any polishing job, particularly one aggressive enough to remove UV-oxidized paint. While far from pretty, that oxidized paint at least formed a protective shell over the color-coat beneath; in the course of removing it, you may have exposed some of the color coat to the open atmosphere. You won't notice it right away, but the exposed color coat will manifest as flat spots later.
The wax you choose is up to you, but synthetic waxes typically offer more UV protection than carnauba waxes. However, while easier to apply and longer lasting than natural carnauba wax, synthetics do tend do give the car a slightly "harder" shine than natural waxes. This hard shine can look fine on a modern or sharply-faceted car, but you might want to go with a softer natural wax if your auto's body is a bit more curvacious.
