A light-reflecting prism

The 42 stories making up the main tower volume are entirely clad in a 51,600 sqm (555,400 sq ft) curtain wall made up of floating vision panels and concave stainless steel spandrels. The glass vision panel is glued to an aluminum frame so as to partly overlap the recessed spandrel panel in a façade design especially developed for the 7 WTC. The resultant modular system is made up of transparent glass panels and slightly undulating light-refracting opaque panels.

The panels of extra-clear glass are placed over the spandrel panels flush with the edge of the floor plates. The effect is to make these front panels seem to float in the air, giving the façade a luminous depth. The stainless steel spandrel panels are slightly concave in shape - with a curvature of approximately 9 m (29.5 ft). This, together with their pressed specular texture, makes the light reflect and refract off the surface in infinite ways, an effect enhanced by two surface treatments: embossing with a light pattern to stimulate abrasive blasting and then corrugation to obtain a horizontal corrugated pattern. The sill in front of the spandrel is clad in a blue plate that reflects the sun’s rays onto the curved spandrel surface so that the whole building façade mirrors the color of the sky.

Standing 25 m (82 ft) high, the podium is made up of two layers of stainless steel slabs separated by an 18 cm (7”) cavity allowing the airflow needed to ventilate the transformers. The panels comprise a series of different-shaped cold-formed triangular-section prismatic profiles placed vertically side by side and oriented at a special angle to create different patterns. The profiles are welded onto a 1.52 x 4.27 m x 25.4 cm (5 x 14 x 0.8 ft) subframe. The front screen prismatic wires all have 12 mm (1/2”) cross section faces and are highly polished, while the back screen prismatic wires have 6.35 mm (1/4”) cross section faces and are glass bead blasted to diffuse and scatter light. The two wire sizes produce complementary light-reflecting properties and reduce the moiré (bifurcating) effect generally created by two layers of parallel lines. The millimeter-precision placing of the triangular profiles set at a series of different angles produces a kaleidoscopic interplay of light and colors, giving the observer a luminous sense of depth. By day, the outer layer of the steel prisms reflects the light depending on their particular orientation while any light penetrating the outer layer is bounced off the surface behind. At night, this porosity is highlighted by LEDs backlighting the outer surface. In addition, an infrared light circuit trips in with the movement of passers-by on the street.