What should be a simple task is often the most difficult to get right. This is the case with car windows. Why should it be so hard to get them clean, household windows aren’t this hard?
Car windows are subjected to far more gunk and grime than household windows. Road grime, fumes evaporating from interior plastics, high-velocity insect suicides etc. Many household glass cleaners are just not up to the task. “So just grab an automotive glass cleaner, right?” Not really. As I mentioned, there are so many different kinds of grime on car windows that no one cleaner can get rid of them all. Each glass cleaner (even if it isn’t stated) is really only good for a few of the many different types. Each type of glass cleaner will also leave behind it’s own type of film on the glass. That’s why when using a new cleaner for the first few times it seems to work great, but after a while the glass just doesn’t seem to get as clean anymore. That’s because the ‘new’ cleaner has stripped off the film etc left by the last cleaner, but now it’s own film has built up on the glass.
Many detailers prefer the “two towel method.” That’s where the glass cleaner is sprayed on and the windows ‘cleaned.’ Immediately after, a second clean, dry towel is used to buff the glass. I use a similar process. I use whatever cleaner I happen to like at the time. Then I pause to lightly mist the glass with clear water or water with one or two capfuls of rubbing alcohol or white vinegar mixed in just before the final buffing. The misting with water and vinegar/alcohol just prior to buffing the glass seems to cut through any film left by the glass cleaner or any grime that the cleaner was unable to remove. I stress misting, because too heavy a spray of water mixture will cause streaks. It will take a few trials to get the hang of doing it.
One trick I’ve used for several years now is using RAIN-X on the insides of the glass. It is a bit more work initially, but just as it repels water and dirt on the outside, it does the same on the inside and lasts much longer. The RAIN-X coating on the interior makes subsequent cleanings much easier.
*NOTE: I recently bought a bottle of CASTROL ACCU-VISION. While it’s rain repelling abilities are about worthless, it does work very well in place of the water mix for final misting, or as a ‘stand alone’ cleaner for lightly dirty windows.