One More London

On this building, Foster + Partners had a breakthrough idea. They eliminated the spandrel and used floor-to-floor glazing, creating a cleaner-looking curtain wall. Until the owner visited the finished building, nobody thought about the visual impact of eliminating the spandrel. Glaverbel supplied a 10 mm tempered coated glass to the defunct Zadra Vetri.  Using our glass, Zadra insulated the glass with a 44.2 laminated glass for Permasteelisa, the curtain waller.

In support of Zadra and Permasteelisa, I met Foster’s project architect, Grant Booker, on site in May 2003. The round building shape and the uninhabited office space allowed us to view a whole series of windows at angles varying from nearly 0 to 90°. The viewer-to-glass distance was important, reaching up to 20 m.  The magnificent view across the Thames or to an adjacent building with extruded aluminum cladding profile provided perfect vertical linear references to the observer’s eye.

Under these stringent viewing conditions, we noticed the linear vertical draw lines. That distortion became unnoticeable in normal viewing conditions: angles from 45 to 90°, 3 to 5 m distances from the glass.

Float glass draw lines are parallel to the flow of glass in the tin bath.  The stretching action of the melted glass flow and the top rollers cause it. These lines are more apparent in thinner glass (1 to 5 mm). 

Why is the draw line distortion more apparent in Plot 1?

In a standard European jumbo, 6000 mm X 3210 mm, it is not possible to cut the larger size glass (3800 mm) across the glass ribbon.  Thus, the draw lines are vertical.