Damaged glass through chemical etching has several causes. It could be from hard water stains caused by rain traveling over concrete, spots of water left to dry on windows or acid rain. Or it could be caused by oxidation, which can happen when metals around windows, such as the screens or window frames, are exposed to rain or humidity and begin to deteriorate. Your windows may look cloudy, with a white haze that won't wash off. This prevents you from being able to see clearly through your windows. There are ways to remove chemical etching from glass, with some materials and lots of time.

Modern glass building
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How to Repair Chemically Etched Glass

Glass is never completely smooth. A microscope will show a rough surface with peaks and potholes. Contaminants fill those potholes and react chemically with glass, bonding to its surface. That causes glass to become stained and discolored. When glass is new, these contaminants are not visible. But over time, glass becomes rough and more contaminants accumulate.

To Get Ready

Make sure you remove the source of the water from the glass. Then gather the following:

  1. For hard water stains, try Restoro or Bio-Clean. For oxidation, try Crystal Clear 550 or Sorbo Stain Remover. For either, you can make your own with 1 gallon of warm water, 1/2 cup of white vinegar and 2 tablespoons of trisodium phosphate.
  2. Soft scouring pad.
  3. Window cleaning squeegee and washer fluid. You can make your own washer fluid with 1 teaspoon of mild dish soap and 1 gallon of warm water.
  4. Bucket.
  5. Clean cloths and rags.
  6. Gloves.
  7. Hand-held polisher or scrubber. For larger areas, use a circular pad on a battery or air-operated drill.

To Wash the Glass

  1. Wearing gloves, scrape debris. Use the window washer and squeegee to clean and dry the glass.
  2. Apply the stain remover as a thin paste to small areas of the stain with your scouring pad. The stain remover must not sit on the glass for more than a few seconds, or it could damage the glass. Only apply enough stain remover at a time that you can scrub.
  3. Scrub the paste using your polisher, scrubber or drill for three minutes in different directions. Make sure you go in all different directions; this is important. It's very easy to skip a direction, which will show in the final result.
  4. Wash the area thoroughly with water and clean cloths.
  5. Check to see if the stain is removed. Repeat if necessary.

This procedure will take a while. It may take repeated washings to get the stain off. When you've finished the job to your satisfaction, try to protect the glass from the water source to prevent repeated staining.