A Dual Action polisher is a polishing machine that uses a circular motion combined with a spinning motion to create a rational double action. This motion is useful when polishing a surface by machine. The Dual Action polisher is famed for being easy to work with, making it ideal for beginners.
A test spot is done to determine what combination of polish, polishpads and technique will give you the best results when correcting a surface. A test spot is done in a small area before you start to fully detail the entire vehicle.
A very common and popular practice on social media is the picture of the 50/50 shot. This shows a very clear line that divides a fully polished section and an uncorrected section. This is done to demonstrate the difference you can get from a full correction.
Overspray is caused by the mist that is created when spray painting a surface. The tiny paint particles are light enough to float around in the air, when they land they slowly start to harden and become overspray. Overspray can be removed safely in many cases.
When a part is spraypainted, a mist of paint can float down onto other surfaces. This can happen when a part of a car is being painted. This mist falls down onto other parts and dries up. This is called overspray and shows up as very small specks on top of the paintwork.