Car Polishing Guide
Polishing is a term which is often used to describe a broad range of car-care activities, but in this case it refers to using a product which contains abrasive material which will actually remove a very thin layer of your car's paint.
Why would you want to do this? Well, because your car can become damaged by scratches, water spots, swirl marks, and acid etching from bird droppings among other things. Polishing your car with an abrasive material can remove the surface of the paint down to a level where the defect disappears. Obviously your car only has a limited amount of paint, so too much polishing will eventually damage the paint and mean a re-spray.
It is not always necessary to polish scratches out completely because some finishing products can act as a 'filler' making the scratches hard to see. This means you don't have to remove as much of your car's paint, making it a safer option, but it's not as permanent a solution.
Not all scratches and blemishes can be removed with polishing. Most modern cars have three layers of paint: Primer, colour coat, and a protective clear coat. Polishing is only useful on defects which affect the top clear coat. If damage has occurred which penetrates down to the colour layer, then polishing down to that layer would remove the protective top layer and expose the paintwork to the risk of corrosion.
You have a choice of polishing by hand or using an electric polisher. Hand-polishing takes a lot of hard work and doesn't have as much of an effect. This can be a good thing if you only have minor scratches and don't want to remove too much paint surface. Using an electric polisher is quicker and easier, and can be used on more severe blemishes. The only problem is you risk damaging the paint through over-polishing. Cars do not all have the same hardness of paint, and if you happen to have a car with hard paint, then polishing will have less of an effect.
Some polishes, especially the more aggressive ones, contain abrasive particles which break down as you use them so that the particle size gets smaller. This is similar to using course sandpaper and then moving to finer sandpaper for a better finish. These polishes are best suited to application with an electric polisher, because hand-polishing is not rigorous enough to break down the particles.
One thing to bear in mind is that polishes do not always just contain polish. They sometimes contain a finishing product such as wax as well. If you're going to wax your car later as a separate stage, then you probably just want pure polish. You should read the label and decide what's best for you.