Volume 43, Issue 2 - February 2008

the Farnady Files

Clearing Things Up
What Could Be Clearer Than Clear?
by Dez Farnady

I have been writing about clear glass a lot lately, but every time I think I said just about enough, something else comes up that gets me back to the subject. This time it is another request to circumvent the law. 

The traditional request for illegal acts in violation of the laws of physics used to be for one-way glass. You remember the question. Can I have glass that lets me see out and people can’t see in? The answer was always no. Now the question is: can I have all sorts of energy performances and keep the glass clear? Well, now the answer is almost yes—but how clear is clear? 

Knowing all this I was not surprised to see this particular skylight glass spec for an art studio. The artist, a painter, was planning to photograph original paintings, probably for the purpose of digital reproduction. In the attempt to attain ultra-pure light and glass clarity for a studio skylight, the specification included everything but the kitchen sink. It had ultra-clear and low-E and then a translucent product. I am not sure what else they could have included but, since Harry Houdini is dead, magic was out of the question. 

If maximum clarity is the purpose, it is pretty certain the last glass you would want to use would be tinted or low-E. It’s pretty obvious why you wouldn’t use tinted glass, but why not low-E? Well, have you ever seen low-E from the outside or at oblique angles? It can play havoc with the rainbow since it reflects wavelength selectively. So for maximum clarity you’re obviously stuck with clear, and not a coated or tinted product. Of course, there is a low-iron option. 

If the skylight has a northern exposure the light is already neutral and, at that point, I am not sure the issue is worth additional pursuit. But I suppose if the artist is successful and can afford the best, why not low-iron?

Playing with Color
The painter’s eye must be tuned into color a lot more than the eyes of those of us whose favorite color is, let’s say, green. Since the iron content of clear float glass creates a green tint on the edge, people assume that this affects the color of the light transmitted. 

On furniture glass, the green edge of clear glass is frowned upon since we now know we can get low-iron glass with a blue edge instead. The all-too-clear edge of water-white was never very popular, but the blue edge of the current group of low-iron products, readily available, has found its way into the hearts of architects and designers who believe they have discovered another panacea for vision glass as well as for furniture. The latest specs arriving on the scene ask for low-iron glass for everything from storefront to residential picture windows because it’s thought to be more clear than clear. 

The color difference is “clearly” apparent on the edge of the glass, but what about looking through it? I have no quarrel with those who prefer the blue edge of Starphire to the green edge of standard clear heavy glass on, say, a tabletop. But is there really a difference in a window or a skylight? I am not so sure I am prepared to pay a premium for the two-percent light transmission difference between the clear and low-iron 1⁄4-inch product in a vision glass application. I don’t think Sherlock Holmes could tell the difference between two windows next to each other if one was clear and the other low-iron.

I do know, and am prepared to put money on the fact, that in a skylight you cannot tell the difference between color neutral products with 10- and 20-percent light transmission differentials. It would be pretty cocky for me to say this if I did not already have the proof. We have a four-panel skylight with three different low-E’s and a clear panel. I have already made money on it, betting glass people (not amateurs), that they can’t tell one product from the other. 

So, my artist customer got the most expensive overkill I have ever sold just to have, presumably, the best. They ended up with satin-etch tempered over heat strengthened laminated Starphire. 

Oh, by the way, the skylight was on a north facing elevation and clear glass would have probably been perfectly fine. The skylight cost about four times more than clear glass option would have been. Okay by me . . .

Dez Farnady serves as the general manager of Royalite Manufacturing Inc., a skylight manufacturer in San Carlos, Calif. His column appears monthly. Mr. Farnady’s opinions are solely his own and not necessarily those of this magazine.

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