Volume 39, Issue 7,
We appreciated the January 2004 Issue@Hand column (see page 4) regarding the controversy over the term “self-cleaning” glass. We were less enthused over Pilkington Building Product’s response in the April issue (see page 6).
While the fusion of molecular levels of titanium dioxide to clear glass is quite remarkable, the benefits of the resulting photo-catalytic destruction of organic contaminants is better demonstrated in the laboratory than in the real world. In temperate and colder climates, with their high rainfall, relative humidity, overcast conditions, industrial pollution, profusion of bird-droppings and vegetation, even photo-cataly-tic destruction of organic matter becomes problematic.
It is axiomatic that the more hydrophilic the surface, the more moisture is always present to provide a perfect medium for reaction with surface contaminants. Rain and coastal spray contain enough dissolved gases, carbonic acid, chlorides, sulfates, nitrates, ammonia and particulate matter to make it chemically active. Similarly, water supplied by municipalities, while safe for drinking, cooking, washing, etc., still contains enough salts, hard water minerals, bacteria, etc. to be chemically active.
When either source of water is allowed to evaporate on the surface of glass it combines with ordinary soil to promote the formation, adhesion and buildup of insoluble mineral deposits, lime scale, rust and soap scum. It is the ongoing exposure to chemically active water that contributes most directly to increased soiling … and to the costly surface damaging cycle that results from scraping and scrubbing to remove insoluble buildup.
Increased “wetting,” “spread” and “sheeting” are important in detergents used to clean surfaces. On glass used in the real world, increased wetting only means that it allows water and water-borne soil to spread over a larger area, but with no reduced adhesion of minerals and contaminants following evaporation of the water. In other words, you still have to clean the glass, but because of its “improved” hydrophilic characteristics, you have to be more careful as to what cleaners to use, and then you have to be sure to flush all of the cleaner and the soil off the surface with distilled water. Otherwise you have actually improved the soilability of the surface.
Glass is a material that enlightened manufacturers have made better by increasing its water and soil repellency through improvements in formulation, manufacturing and finishing/polishing. The benefits and utility of glass outweigh its propensity for soiling due to the environment. Clean up the air and de-mineralize the water and glass will, indeed, be virtually self-cleaning.
Howard G. Ohlhausen
Editor’s note: Unelko Corp. is a manufacturer of water- and soil-repellant coatings for glass.
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