As an avid auto detailer to my cars, I love crystal clear and clean glass on a car.
I can tell you, Windex is the absolute worst to use to clean glass.
How much is an approximate quart size (less than that even, aren't they?) bottle of Windex these days? $3? $4? Think what is in your car that is used to rid the windshield of extremely heavy grime? That's right, windshield washer fluid. I have tried multitudes of products for cleaning the car windows, and some of them do indeed work well, but windshield washer fluid is a whole $0.99 for a gallon of the stuff. You can have 3 or 4 gallons of the stuff for the same cost of that little bottle of Windex.
Also technique has a lot to do with it. This really applies to car windows because I would assume they get far dirtier than any house window, but I do imagine house windows can be similar. The first pass of cleaning a window, you are picking up a lot of dirt, but also are smearing a lot of dirt and grime around. My wife does that all the time, sprays the Windex, then wipes with a paper towel and that's it. Then she wonders why the window is all streaky. She also uses the same paper towel for all windows.
I spray the windows of the car once fairly heavily and wipe them with a paper towel (always Bounty, no other paper towel will do for me.) Then I dry that with a clean dry paper towel. Folding that 2nd towel over, I again spray a 2nd time and wipe with that 2nd towel and dry that with a 3rd. If it needs more, then it is repeated, but this usually has the windows completely clean and streak free.
Moving on to the next window, the 2nd paper towel used on the first can now be used for the first wiping and the 3rd towel used for the first drying, etc. By the time I am done cleaning the windows of the car, I have a whole pile of paper towels, yet the house has twice as many windows each with twice the surface area of a car window, yet my wife uses 1 paper towel to do them all.
And my wife still insists on paying $3-4 for that little bottle of Windex instead of $0.99 for a whole gallon of windshield washer fluid that works a thousand times better than Windex
