Step 7: Get rid of stubborn spots

mineral-stained glass windowpane on the left to compare with supercleaned pane on the right
Photo: Kenneth Chen
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Over time, hard-water runoff from masonry or rain falling through metal window screens leaves stubborn mineral stains on glass that normal washing can't erase. So after a regular cleaning, Weingard wets the glass and gently "supercleans" it either with fine 000 steel wool (if the panes are small) or with the cleansing powders Zud or Barkeeper's Friend, which contain oxalic acid. (Other brands of powder may scratch the glass or fail to remove stains.) He mixes the powder into a paste on a wet towel, rubs away the stains, then rinses and squeegees the glass twice to remove the residue. Even with that treatment, the staining generally comes back in about six months.

To get rid of stains for good, Weingard recommends the application of 3 Star Barrier Glass Surface Protectant, a clear polymer coating. "After the stains are gone, you just put the coating on with a strip applicator and squeegee it off," he says. Protection against staining is permanent, as long as the polymer is reapplied after each regular cleaning.
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    Tools List

    • Squeegee
      Squeegee
    • Strip applicator with cloth head
      Strip applicator
    • Chamois or lint-free rag
      Chamois, and a lint-free rag or two
      like a cloth diaper or old linen napkin
    • hacksaw
      Hacksaw
      to custom cut squeegee for multipane windows
    • utility knife
      Utility knife

    Shopping List

    1. Dishwashing liquid

    2. Super-fine (000) steel wool

    3. Mild abrasive cleaner, like Barkeeper's Friend

    4. 3-Star Barrier Glass Surface Protectant clear polymer coating

    5. Natural sponge (optional)