Volume 11, Issue 1 - January/February 2009

Off the Line
How Do I Get My Glass Clean?
by Russ Corsi

WHETHER IT'S CLEANING your windshield or cleaning your windows on your home, one of the questions asked most often by individuals attempting to clean the glass is, “What is the best way to clean my glass?”

Before one can thoroughly clean glass, it’s often helpful to determine what makes up the substance that is making the glass dirty. 

Contaminants can fall into four general categories: 
• particulates;
• surface residue;
• reaction contaminates; and 
• surface corrosion.

Particulates are solid materials loosely deposited on the glass surface. Any good glass cleaner (such as the “blue stuff” that we all use) works just fine to remove particulates.

A surface residue can best be described as an oily contaminant that cannot be removed with the “blue stuff.” Most residue can be removed using a 50/50 iso-propanol (alcohol)/water mix or by using a detergent (soap) solution.

Reaction contaminants are very aggressive and often undergo a chemical bond with the glass surface. Hard water salts are the most commonly identified reaction contaminants. In some parts of the country, city water supplies often contain large quantities of inorganic compounds. If one knows that their water is considered “hard,” it’s important to re-wash glass with de-mineralized water any time that it has been determined that the “hard” water was used to clean the glass. Glass that becomes coated with a large amount of the hard water salts bonded to the surface is extremely difficult to clean. Highly acidic solutions will attack the salt but do create human safety and environmental concerns. Therefore, it is not recommended that the acidic solution be attempted. If the salt contamination is located in the vision area of a windshield, it is recommended that the glass be replaced.

Surface corrosion is a contaminant that the glass wholesalers and installers must be able to identify and to be ready to address. Surface corrosion is a glass surface degradation that results from glass that has been stored in high-temperature and high-humidity conditions. This type of contamination will exhibit a semi-opaque characteristic that can be mistaken for deposited dirt. If identified early enough, a cerium oxide solution may remove the corrosion. Cerium oxide is diluted with water and made into a slurry that can be worked into the glass in a circular motion (similar to waxing a car). The slurry is then washed off with water or cleaned with the “blue stuff.” If the corrosion is not successfully removed, a blue or white stain will remain on the glass. 

It would be nice if dirty glass was either caused by particulates or surface residue to assure that the glass can be cleaned. Unfortunately, the other two conditions do exist and do cause a lot of grief for anyone attempting to clean their glass.

Source: PPG Industries Publication “Recommended Techniques for Washing Glass,” circa 1980. 

Russ Corsi retired as manager of technical services from PPG Industries’ Automotive Replacement Glass business unit after 31 years in the glass industry. He now serves as a consultant to the industry. Mr. Corsi’s opinions are solely his own and not necessarily those of this magazine.

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