Dichroic Glazing Comes of Age

Oct. 1, 2008

Dublin's No. 1 Grand Canal Square comes to life with large-scale dichroic glass and an innovative, contemporary design

By C.C. Sullivan 

Can glass change a country's image?

In the southern docklands of Dublin, the new real estate development Grand Canal Square suggests it can. This assemblage of three unique office blocks, complemented by a striking theater and public concourse designed by architect Daniel Libeskind, projects a compelling image of modern Ireland.

One of those buildings, No. 1 Grand Canal Square, designed by Dublin-based DMOD Architecture, demonstrates the inventiveness and technical prowess of the country's own architectural talents. Through the use of anti-reflective glazing and unusually large panels of its technological cousin, dichroic glass, this office building now serves as a commanding landmark for this prestigious mixed-use development.

According to DMOD architect Des Hourihane, the design team envisaged a relatively minimal building shell that would be as transparent as possible yet be animated and engaging for passersby. The project team gathered their inspiration from James Carpenter, the New York-based architect and glass artist renowned for his use of light and glass materials. Carpenter was among the first to experiment with dichroic glazing, which changes apparent color when viewed from different angles. When light is passing though the material, it may look gold or green or blue; when light is reflected, the hue changes.

"We knew the dichroic material had potential but we didn't realize how much it really had until we used it," Hourihane says. And for good reason: The manufacturer had just perfected the means to fabricate large, monolithic sheets of dichroic-coated glass. Before No. 1 Grand Canal Square, dichroic glazed openings were limited to 1 or 2 feet in their largest dimensions.

For this new office building, the project team would take advantage of consistently coated panels of about 10 feet by 12 feet - sizes unheard of before, even for Carpenter. Working with Neil Murphy, a cladding and glazing consultant with Dublin's Billings Design Associates, the team created a curtain wall with slender steel mullions using two types of glass: the anti-reflective panels and dichroic sheets that range from blue to green to gold. Further animating the façades is a system of laminated, double-glazed structural glass fins that provide lateral support for wind loads. In between the fins, the anti-reflective glazing glass gives the appearance that the steel structure behind is exposed.

Fins jutting out of the facade, made of dichroic glass, are used to support the curtain wall laterally for wind loads. BDA/EVIN MCCARTHY

The dichroic fins are hard to miss. Engaging and colorful reflections radiate from the triple-laminated, low-iron sheets, thanks to their inner layer of 6 millimeter annealed glass coated with a dichroic formula of silicon and titanium dioxides. According to Murphy, the two outer laminations were toughened for strength and all of the glass was bonded into a thermally broken steel shoe with four safety restraint pins that run into the outer laminates in the unlikely case that the adhesive bonding ever failed. Though two studs hold the outer sheets of the glass, the glass itself essentially provides structural reinforcement to the four-story curtain wall.

Advances in glazing technology made No. 1 Grand Canal Square possible, says Martin Potter, a London-based international sales manager with Schott, which made the dichroic panels. "The problem with dichroic glass was that it was usually just available as a film, in the interlayer, which gave it an undesirable, oily effect, with all the colors of the spectrum," he explains. "The glass fins DMOD designed are large, using a very stable dichroic coating on the glass."

Potter adds that the coating is the same metal oxide as the one that reduces reflectivity on the flat panels; when applied in different thicknesses and layers, the glass takes on its colorful variability. The technology stems from the American space program, which originally developed the material - also known as fusion glass - for spacesuit visors and satellite mirrors. Some glass varieties have up to 65 extremely thin layers of metal oxides including titanium, gold chromium, and silver, adding up to a thickness of perhaps 3 millionths of an inch. The metals are vaporized in an airless vacuum chamber with an electron beam, and the vapor condenses onto the glass in crystal form; in some cases, the coating is finished with a protective layer of quartz. These layers create an "interference filter," in industry parlance, which works without any gels or color-enhancing coatings.

The Grand Canal Square development serves as a landmark to commercial, cultural, and architectural development with its contemporary design and memorable building images. An office tower in the development, No. 1 Grand Canal Square, employs monolithic dichroic glass on a large scale only recently made possible by manufacturers. BDA/EVIN MCCARTHY

The permanent, chemically stable coatings are weather resistant and have been shown to resist fading; they can be fabricated, laminated, and modified in various ways. The resulting and unique trait of dichroic glass: Its transmitted color and reflective color are completely different, and the apparent color of the glass also changes in reference to the viewer's position, with up to 100 color variations including gold/blue, blue/pink, and violet/gold.

The application of this space-age technology required careful design and specification, says Murphy. "We were impressed with the variety of effects this glass created as an aesthetic element, so we wrote a performance-based specification for the glass façade, and the client wanted us to ensure we got the exact design intent," the consultant recalls. "We weren't forced into accepting an alternative proposal to do something cheaper where the aesthetics suffer. Our clients were very supportive, so we effectively got what we designed, which is very unusual in this day and age."

Just as important as the dichroic glass was careful detailing of the metal structure, says the architect Hourihane. The visible external metalwork of the structure could not be used to hold the fins because of its interference with the color of the building. Adding to the challenge, the project's developer, Chartered Land, wanted to show off the structure by using large clear spans. That meant using as few spandrels, support profiles, and point-fixing elements as possible.

Created for the U.S. space program, dichroic glass was originally used for spacesuit visors and satellite mirrors due to its ability to filter dangerous infrared and ultraviolet rays. Only recently, however, using a so-called "sol-gel process," have manufacturers been able to produce stable dichroic glazing panels available on a large scale in full sheet sizes of up to 10 feet or more, in thickness ranging from 3mm to 10mm. SCHOTT

The result is a glass box - but unlike so many minimalist glass boxes built these days, this one lives up to its vibrant neighbors, such as Libeskind's characteristically energetic theater and a checkerboard office block nearby. Even more important, this building is helping draw attention to Ireland and its capital city's transformation. Dublin's dockland development, now attracting leading businesses from around the globe, is set to become a new cultural and commercial epicenter of Europe.

C.C. Sullivan ([email protected]) is a communications consultant and author specializing in architecture, design, and construction technology.

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