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For decades now, window cleaners have reported encountering glass with a “rough surface” that has a “drag sensation” and exhibits a “tinkling sound” when a razor blade is passed over the surface. This type of surface has historically been described as fabricating debris in varying amounts. Historically, “fabricating debris” has been described as particles that were not adequately washed off prior to entering the tempering oven, thus getting fused or “baked” onto the surface. However, research by the IWCA in recent years has shed light on some inconsistencies in that theory.
For decades now, window cleaners have reported encountering glass with a “rough surface” that has a “drag sensation” and exhibits a “tinkling sound” when a razor blade is passed over the surface. This type of surface has historically been described as fabricating debris in varying amounts. Historically, “fabricating debris” has been described as particles that were not adequately washed off prior to entering the tempering oven, thus getting fused or “baked” onto the surface. However, research by the IWCA in recent years has shed light on some inconsistencies in that theory.
First, lab tests that attempted to fuse glass particles and sand to flat glass failed. After heating and cooling glass contaminated with particles failed to produce the fusion.
Second, powerful microscopes attempted to detect fused particles on actual samples of offensively scratched glass from the field. No such particles could be identified.
Third, after more than five years of searching, no actual physical specimens of glass tainted with fused fabricating debris have been delivered to the IWCA. However, we were able to gather scratched glass samples from actual construction sites in all parts of the country. Sure enough, these scratched glass samples exhibited a “rough surface” whereas many times similar glass windows on the same job site exhibited a smooth surface and did not scratch even though the same cleaning methods were used.
Fourth, at last years IWCA Convention we introduced the idea that the rough surface of glass that appears more likely to scratch could be due to a change at the micro or nano level, and the term nanoscale roughness was introduced. There is an entire field of science that discusses how surfaces with a nanoscale roughness may be more prone to physical damage. The question remained however - how do the “rough surfaces” that are encountered in the field originate? Do they develop during the tempering process? Or are there other considerations? Could the development of such nanoscale roughness go back to the actual float glass process where glass is made on a bed of molten tin - producing what is known as an “air side” and a “tin side”?
It is interesting to note in the IWCA collection of scratched glass with “rough” surfaces the tin side usually corresponded with the rough side, which corresponded with the scratched side. Should this surprise us? Is it possible that the tin side of float glass can develop a "random roughness"?
To begin to understand this, I direct your attention to the paper “Statistical Analysis of the Metrological Properties of Float Glass” by Brian W. Yates and Alan M. Duffy. This paper speaks of a “surface roughness” that develops on the tin side of float glass and reports “It can be seen that the overall tin side surface roughness average is indeed rougher on average than the air side”. The conclusion reads: “Statistically significant differences were found between the tin and air side surface roughness values for both untreated and acid treated, with the tin side being significantly rougher than the air side.”
Is there a definite link between the rough tin side of some glass surfaces and surface scratching? Does post production heat treatment of glass exacerbate the roughness of some glass surfaces? These questions will be closely examined as you are about to see.
Armed with this knowledge, questions and the collection of scratched glass samples, the IWCA has embarked on the first of its kind scientific research during the summer of 2016. Dr. Paul Duffer has led the way for the IWCA to participate in a special research program at the world class Department of Materials Science and Engineering at Pennsylvania State University. Professor Seong Kim, phd is dedicated to materials science and has much experience with glass surface studies. He will oversee the IWCA research of scratched glass at Penn State.
The IWCA is dedicated to helping window cleaners better understand the glass surfaces that window cleaners work on daily. Armed with knowledge as an industry we can develop cleaning methods and practices that will assist us in maintaining the integrity and beauty of glass, reduce possible damage, and adequately protect ourselves should aggressive cleaning techniques and restoration become necessary on a job site.
Please, stay tuned.
Paul West
IWCA Glass Committee Chair
kohalapaul@gmail.com
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1 comment:
Well this post should certainly be informative for a lot of people out there. And i myself had these questions. Thanks for sharing this and keep it up.
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