Volume 38, Issue 3, March 2003


Multiple Shades of “E”
More to Your Low-E Than Meets the Eye
by Dez Farnady

My low-E trials and tribulations may never end, but now and then they arrive with a new little twist that continues to contribute to my education in the glass business. So as new twists arrive with new products I try to fit them like puzzle pieces into my software. Recently I found another interesting twist that I had suspected but had never seen. 

Our production manager came into the office one day to ask me to go out and see some glass that was “absolutely unacceptable.” 

I walked out into the yard knowing he did not need to point out that one of our little ten-lite skylights looked as though it was about to morph into a rainbow. The morning was drizzly and overcast and the light was soft and gray. 

The glass was second-generation performance low-E. We checked the glass closely and it all passed the flame test. When you hold a flame close to the insulating glass surface it shows four reflections. The reflection from the low-E coating is a distinctly different color and can show you the surface to which the coating is applied. The yellow flame was on the number two surface for all of the units except two that were a deep-purple color and where the second flame was held the glass was a bright green. The two rectangles on both sides, right next to each other were the problem units. One was a dark purple and the other was virtually clear. All the glass was from the same fabricator. 

There are no color inconsistencies with the low-E used in this home. I called our supplier and told him to come and check out their glass because we had a problem. Their two representatives got to the shop about noon, when the sun was high in the sky, and as we looked at the glass the color difference was not all that bad. It was still there, but now it looked as if it was perhaps just the wrong surface coating or possibly from a different manufacturer. The full light of the sun had subdued the radical colors we had seen that morning. The guys inspected the glass and then inspected me, looking at me like I was some kind of a rookie, probably thinking to themselves, “What’s he making such a big deal about, just that slight color difference?”

Further Examination
The plot continued to thicken. Further investigation revealed that all of the glass had not arrived at the same time. There had been replacements on some of the units. It turned out that the triangles and rake units were from the same fabricator but not from the same manufacturer as the rectangles. Normally, even under the worst circumstances, mixing manufacturers is a no-no and I still have not figured out why it was done, but as it turned out that was not to be our problem. The reason our supplier was such a Johnny-on-the-spot was because he figured that the color difference between the two manufacturers was going to be the complaint. If it were not for the logo, we would have had trouble distinguishing the manufacturers, particularly on the units that were green. The big difference (although not nearly as big as it had been in the morning) was between the adjacent rectangles. We double-checked those and they clearly came from the same place. 

Later that afternoon, I took our sales manager out to look at the glass. The sun was shining from the west directly on to the glass and he too thought I was nuts. There was almost no difference between any of the glasses. Even the flame test betrayed me by showing a nice soft yellow flame on the second surface of every unit. By then I was starting to think I was nuts. 

First thing the following morning, before the sun got over the top of the building next door, in the gray dawn light, I checked again. Big as life, the purple glass was back again. I was not crazy after all. For the sake of my credibility I made the glass inspector come back again the following morning to see the purple glass for himself and acknowledge that we were looking at a defective coating. 

Scientific Findings
The unscientific conclusion from this recent experience confirms that in fact low-E coatings are wavelength-selective and you better watch your wavelengths. Not only is it possible for manufacturers to put out a defective product, but it may also be difficult to spot the defects under varying lighting conditions. Differences in daylight as well as the angle of view can radically affect the appearance of low-E glass. The lack of uniformity in the appearance of even good glass that is expensive and is supposed to be perfect in looks and performance is often thought to be grounds for rejection. Defective glass is one thing, but those color differences—even in good glass—can occasionally cost someone a lot of money. 

Meanwhile, some people out there still think I am crazy because I see purple. 


Dez Farnady
Dez Farnady
serves as general manager of Royalite Manufacturing Inc., a skylight manufacturer in San Carlos, Calif. His column appears monthly.


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