Did you ever know that glass is not completely smooth? Under a microscope, glass reveals a rougher surface made of peaks and potholes. Organic and inorganic contaminants often carried by water fill those potholes and react chemically with the glass, firmly bonding to its surface. As a result, glass easily becomes stained and discolored.

When the glass is new those potholes are so small that even settled contaminants are not visible. But overtime glass exposed to water or intensive mechanical cleaning becomes even rougher and potholes can accommodate much more deposits. That process of glass deterioration is also called glass corrosion. To conclude, there are two factors affecting glass staining: glass corrosion and exposure of contaminants dissolved in water.


RayAccess, Inc. are experts in Glass Stains Removal. There are different types of stains that can appear on the glass. Here are the most common:

  • Hard water stains
  • Glass Oxidation
  • Chemical damage (as acid or alkali etching)


Hard Water Stains are the most common type of glass damage. They can appear as grey or white hazy stains with the shape of water drips.  Basically, Hard Water stains are a result of glass corrosion due to constant exposure by water and concentration of inorganic compounds dissolved in water (TDS). In regular water, there are hundreds of different ions of dissolved materials, the most of them are calcium (Ca+2), chloride (Cl-), magnesium (Mg+2), sodium (Na+), sulfate (SO4-2).   Solids dissolved in water literally stuck in the rough surface of the glass and react chemically bonding with the glass. The result of those chemical reactions is insoluble compounds that can be removed only mechanically or chemically.

The most common areas of Hard Water Stains are shower doors, windows located near irrigation sprinkler or areas of constant water dripping (for example, under the defected flashing or gutter joint). In rainy season water running down the building can also cause hard water stains carrying an excessive amount of dissolved materials from stucco, concrete and so on.

Please see methods of Hard Water stains removal below.


There are two ways to avoid Hard water stains appearance.

  1. Stop glass corrosion by eliminating the water exposure if possible. For example, redirecting or improving irrigation system around a building.
  2. Protect the glass from corrosion by applying sealer on the glass surface. Most of the glass sealers can provide 1-2 years protection depending on sun and water exposure, and then need to be reapplied. Important: often glass needs to be cleaned from Hard water stains before sealer application.


Glass Oxidation occurs when metal screens or frames around windows are exposed to rain or humidity and deteriorate causing oxidation. These products of oxidation run down the windows and penetrate or cling with the glass. It’s appeared as almost clear to grey hazy staining right below frames or metal elements on the exterior of a building.

Glass and Metal Protection with special sealers can significantly reduce the probability of oxidation.


Aggressive chemicals contained acid or alkali can significantly speed up cleaning procedures of the glass but at the same time, they can make even more damage. Those chemicals react actively not only with contaminants but also with the glass causing intensive glass corrosion with staining called etching. Etching goes much deeper in glass structure comparing with hard water stains and oxidation. Therefore, removal of etching requires deep glass restoration pretty similar to Glass Scratches Removal. Etching looks as hazy stain reflecting the area of chemical application.

In most cases, chemical damage happens during attempts to use acid or alkali to remove hard water stains, oxidation, construction contaminants or in routine cleaning. Frankly, acid or alkali solutions are acceptable on some type of clear tempered glass, but in most cases are not. At least preliminary test in a hidden area should be implemented before using of the aggressive chemical.


In common classification, there are 2 stages of severity of glass stains. Actually, those stages are more about glass corrosion then stains. Because then deeper corrosion in the glass structure than more severe glass stain and then more difficult to restore glass to original clarity. Glass stain (corrosion) close to the surface is Stage 1, deeper in glass structure are Stage 2.

Next test can be applied to recognize stage of glass staining. Make stain area wet, if you still can see the stain on a wet glass most likely this is Stage 2, if not it’s Stage 1.

The efficiency of stain removal process depends not only on the depth of the corrosion but also on what kind of chemical reactions and bonds created between contaminant and glass. Therefore, even if it’s Stage 1 corrosion, removal trial should be applied on small and the most exposed area to understand how efficient glass restoration would be.


There are two methods to remove glass staining and restore original clarity of glass.

Method 1: Chemical removal

Chemical removal is based on an idea of dissolving contaminants and their bonds with glass by more aggressive chemical reagent as acid or alkali.

Advantages: It is the fastest and less expensive way to remove Stage 1 staining.

Disadvantages: Chemical Removal is very risky with high probability to etch the glass and increase corrosion. Chemical removal works with certain types of clear glass and a certain type of stain. After the dissolution of contaminant deposits, there is still the same corroded glass with deep potholes. So, glass must be protected with a sealer. Otherwise, hard water stains or oxidation will reoccur in short time. Also, there is certainly potential damage to the environment by application of aggressive chemicals. It can be hazardous for an operator if he doesn’t wear proper personal protective equipment.

Method 2: Glass Polishing

Glass polishing allows to mechanically remove contaminants and flatten back glass surface.

Advantages: Glass Polishing works perfectly with any type of glass and the most of Stage 1 and 2 staining. The result is polished and flattened glass surface that significantly reduces the possibility of stain reappearance. Glass polishing also can remove small glass imperfections and chemical etching.

Disadvantages: Glass Polishing is more time consuming and expensive then Chemical Removal. Restoration process requires the application of special equipment like buffer with adjustable RPM, polishing pads and polishing compound, pads for corners and etc. Glass Polishing requires special skills and experience in glass restoration due to the possibility to scratch or mechanically damage the glass. Glass protection by sealer is also recommended.

However, if glass corrosion is so deep that even Glass Polishing can not remove the stain. There is also Glass Abrasion method mostly utilized for scratches and glass imperfections removal by resurfacing the glass. See also Glass Restoration for more information about Glass Abrasion.

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