[COLOR=#0000ff][SIZE=4][B]This article is a post from my blog copied to this forum.
[COLOR=#333333][FONT=Arial][COLOR=blue][B]It is very important when removing hard water deposits from window glass to watch for abrasion haze. This is the result of either the wrong polishing technique or the use of the wrong polishing medium, or both. I have seen it so bad it was easily seen even on a cloudy day. Although it is usually only visible in the direct sun. Sometimes only at the right angle in the direct sun. Second story windows are more likely to show it up. It appears as many waves of zillions of microscopic scratches. In any case however it is grounds for a lawsuit if the customer sees it.[/B][/COLOR]
[COLOR=blue][/COLOR][COLOR=blue][B]The best way to avoid it is to always use any pad or polishing surface completely flat on the glass. My new Gyro Wheel makes this very easy. Next make sure your superabrasives are indeed opticaly safe. One way to do this is to experiment with your “complete system” on a new mirror blank. Then hit one half of the area polished with a solution of battery acid. This is around a 37% solution of sulfuric acid. You could also use a 1 to 2 percent solution of hydrofluoric acid. These acids will greatly accent any scratches left behind by your polishing process. The side of the polished area of the glass which has not been touched will serve as your control. If you see any abrasion haze I personally would not use that system but rather look for another.[/B][/COLOR]
[COLOR=blue][/COLOR][COLOR=blue][B]Another way to make absolutely sure you are safe after performing the mirror test is to do an on site test. Do it on a bright sunny day. If you are intending on doing second story windows wait until around two to three in the afternoon. Then clear the stains off a two by two foot section of the window. Stand back about fifty to a hundred feet and look real close. You shouldn’t see any waves.[/B][/COLOR]
[COLOR=blue][/COLOR][COLOR=blue][B]The greatest haze is usually caused by using circular pads turned on edge (ripping the surface). Companies will do this using cerium oxide straight out of open containers. By first wetting the window, touching the edge of the wet felt pad to the dry powder, then running the edge of the pad across the window. This technique even if the cerium oxide is optical grade, will create severe abrasion haze. Which can easily be completely invisible except in the direct sun.[/B][/COLOR]
[COLOR=blue][/COLOR][COLOR=blue][B]I have many reasons why I would never suggest using acids that etch glass like hydrofluoric, sulfuric, or ammonium bifluoride. One of which is the fact that once someone has left an abrasion haze by ripping the glass, such damage can be greatly accented by the acid. As I have shown by the first test sited. Further, you will never know if such damage is present because it has been hid/covered over by new hard water deposits. The customer might never have even noticed it when the stains were removed the first time with the cerium. But now this damage is very visible. The customer will then be able to easily see it. And you will be held accountable for “scratching” the windows.