'Cloud Gate' Sculpture and Crown Fountain
Monuments Required Planning, Plenty of Work Before Construction
The two pieces of art on Millennium Park's western edge are
monumental, and so is the work that it took to get them there.
The two works are "Cloud Gate," a sculpture by
British artist Anish Kapoor, and the Crown Fountain, a creation
of Spanish artist Jaume Plensa. As impressive as these works
are in completed form, the story of their design and construction
is equally compelling.
A Surpassing Cloud
"Cloud Gate," a 66-ft.-long, 33-ft.-high bean-shaped
sculpture, began with the effort to produce a composite model
of the work, said Ethan Silva, president of Oakland, Calif.-based
Performance Structures, which produced the finished piece.
The company toiled through several attempts to reproduce in
miniature a design acceptable to the England-based Kapoor.
The models were molded of high-density polyurethane foam
weighing 16 to 20 lbs. per cu. ft.
Once a model received Kapoor's blessing, it was used to design
Those included the outside shell, as well as the stainless
steel "stiffeners" and internal structural components.
"We needed to find a way to support the shell without
overloading any given point," because to do otherwise
would have risked the eventual formation of indentations,
Silva said. "We also had to allow for expansion and contraction.
You have over 120 degrees of temperature variation, and different
parts of the sculpture at any time could be different temperatures."
The secret to dealing with temperature changes was to allow
each part to move relative to other parts without excessive
constraint on any one component. Two large rings inside the
sculpture move somewhat independently of one another, in turn
supporting the shell. That means the shell had to be permitted
some movement independent of the rings, Silva said.
Three-dimensional modeling software was used to create the
168 stainless steel exterior plates, each with stiffeners
welded on, that make up the shell.
"We used a computer-controlled cutting method to cut
all the parts, so they would fit in the shape we needed,"
To bring those exterior plates together requires full-penetration
welds at the seams. After that welding, seams are to be ground
perfectly flush and polished to a mirror finish.
Some of that work was completed before Millennium Park's
opening, but the bulk of the sculpture has yet to be welded
and polished, which is why visitors can still see seams in
Keeping Sculpture Up
The shell of the sculpture alone weighs 80 tons, the entire
structure 115 tons. That heft has spurred the question of
what keeps such a heavy object from crashing through the roof
of the Park Grill, the restaurant below.
The answer is in the retaining wall separating the Metra
train tracks from the North Grant Park garage. The wall travels
along the back side of the restaurant and supports the sculpture.
The Kapoor is further buttressed by lateral members underneath
the plaza anchored to the sculpture's interior structure by
All the interior structure and about one-third of the shell
components were assembled in Oakland to test their fit. Then
these parts were disassembled and shipped to Millennium Park
in containers aboard trucks.
Workers began assembling the interior structure at the park
in February. Assembly work began on the shell in April and
was complete by the end of June.
"The sculpture is completely unique in terms of what
it is, what it looks like, its setting and what it means to
the people of Chicago," Silva said.
"But all that being said, we'd like to do another one."
Fountain Overlooks Pool
The Crown Fountain features two glass towers rising from
a reflecting pool.
Each tower is 50 ft. tall, with footprints measuring 16 by
23 ft. They soar out of a 0.25-in.-deep pool that is 42 ft.
wide and 222 ft. long and are centered on a plaza created
from the same granite as the pool and measuring 84 ft. wide
by 276 ft. long.
Upon the towers' facades are moving images of faces of typical
Chicagoans. The images are made possible through the same
light-emitting-diode technology that lights scoreboards in
Water rises through the middle of each tower, spills over
all four sides and cascades down the glass bricks sheathing
the LED screen.
Piping also carries water up the tower and spouts it from
a gargoyle-like nozzle in the middle of each tower.
"When we filmed all the subjects' faces, we converted
the video to an electronic file, and electronically manipulated
the image so the mouth would come at or near this nozzle,"
said Roark Frankel, vice president and project manager of
Chicago's U.S. Equities, a real estate company that also handles
project management and development management for third parties.
"So when they purse their lips, it appears water is coming
from their mouths."
U.S. Equities custom engineered a solution that allowed the
piping to pass through the LED screen without interfering
with the display. "It was eight months worth of trial
and error, testing and going through wrong turns," Frankel
The towers were constructed of a thin stainless steel, created
in the form of a grid. The glass bricks were inserted into
each opening in the grid. The front joints of the glass were
then sealed with silicone to waterproof the structure. Silicone
was chosen for its clarity.
"You don't really see the stainless steel grid, and
you don't see the mortar," Frankel said.
Barcelona-based artist Plensa insisted that the fountain
represent a cross section of the Chicago population. So U.S.
Equities studied city demographics and assembled a cast that
would closely reflect the city's gender, ethnic and age makeup.
All the filming was handled by School of the Art Institute
faculty advisers and students. To obtain the required 1,000
images, many more than 1,000 faces were filmed, Frankel said.
The fountain's design goal was to capture and reuse as much
as 97 percent of the water. At the base of the towers and
in the reflecting pool are large reservoirs that collect and
Approximately 11,000 gallons of water are recirculated per
minute, and the pool is self-leveling, with automatic adjustments
taking place about every five minutes.