Etch is when minerals bind to glass molecules. It has to be polished out with specific polishing compounds. I purchased a used car only to realize later that it had obviously spent its life outside as the windows had permanent hard water stains. Another example is vehicles including boats that park at Tilbury, North Delta. There are cement factories there that emit a fine dust that will bind with glass readily, all it takes is the morning due to settle on your generously dusted vehicle or boat and the adhesion process is then complete. The detailing department in Mercedes 3 Point Motors will take you through the steps and costs to deal with this. SHC Autographx managed to polish out the extent on my vehicle, and then add a ceramic coat to all surfaces of my vehicle. This has so far been a very effective solution.
