First of all soap and squeegee the window. Then flip your hand over so the back of your fingernails are touching the glass, Then lightly move your hand back and forth over the window. You will be able to easily feel any and all raised inclusions. Which window cleaners usually call glass fines. These can be felt even beneath low e surfaces. In fact it is sensitive enough to even feel thin soap films. If you rub some soapy water on a small area of a window that has been squeegeed you will be able to feel the soap film.
Simply put this technique is much more sensitive than a penny for detecting how smooth or rough a window surface is. And you have your nails all the time. Just flip your hand over and you can test any window. Here is a very interesting discovery. And I am sure you will discover more. Some windows have rather large raised inclusions but are very smooth between them. Then other windows are very rough but have no inclusions. This is a great method too to couple with pure water or vapor to test for the use of acids that etch. If there are any mineral deposits based on silicates or silica you will be able to feel these. Even water with a TDS of 0 from a Water Fed Pole system can leave spots based on silica. That can be seen in the direct sun, detected with fog, or felt with the back of your fingernails.
This is how you can prevent scratching windows and keep yourself from any lawsuits.
Written by Henry Grover
