[Brent Hollen]

Sometimes, different substances get on windows. If it's left on the window for a long enough time, a stain is created that won't come off. There is a chemical reaction with the glass that occurs, called etching.
The glass being used nowadays is softer than the glass in older windows. It gets etching more easily.
         
* Neglecting windows for more than a year may cause etching into glass from the minerals in dirt and rainwater, causing permanent stains.
* Salt water spray (for homes near Puget Sound) has lots of minerals in it. These windows need more frequent cleaning to preserve quality.
* Sap from plants and trees in late spring and summer can be very acidic.
* Plants, bushes and trees that stay in contact with windows may cause etching.

[Kev Martin]

How strange!!! 

Not that I am questioning your knowledge but how does something like glass that is fully vitrified surely and fired at well above 1300 Degrees become prone to Acid Etching?  Can you explain in a little more detail for me please or perhaps someone else?  I have no intention of leaving Stone Restoration and going into window cleaning by the way .  I am just curious!

Kev Martin
Marble Life Ltd