Standing thirty-three feet high and sixty-six feet long, Cloud Gates has become one of Chicago’s most iconic structures. Known by many as “the bean” (because of it’s resemblance to the tiny legume), the sculpture was designed by British artist Anish Kapoor. But it was brought to life thanks to the hard work of more than 100 metal fabricators, engineers, technicians, and yes, even welders.

Kapoor says the sculpture was inspired by liquid mercury, and so it is forged of a seamless series of highly polished stainless steel plates. In order to bring “the bean” and it’s outer shell to life, two companies on opposite sides of the country were hired. Performance Structures Inc. (PSI), in Oakland, California, and MTH, in Villa Park, Illinois.

Having in-depth experience creating shell structures, initially on ships and later on other art projects, PSI’s Ethan Silva was uniquely qualified for the shell structure fabrication task. Anish Kapoor asked the physics and art graduate to provide a small-scale model.Standing thirty-three feet high and sixty-six feet long, Cloud Gates has become one of Chicago’s most iconic structures. Known by many as “the bean” (because of it’s resemblance to the tiny legume), the sculpture was designed by British artist Anish Kapoor. But it was brought to life thanks to the hard work of more than 100 metal fabricators, engineers, technicians, and yes, even welders.

Kapoor says the sculpture was inspired by liquid mercury, and so it is forged of a seamless series of highly polished stainless steel plates. But underneath the plates is where the majority of the work took place. In 2007, the American Welding Society awarded Cloud Gate with the Outstanding Achievement in Welding Award.

In order to bring “the bean” to life, two companies on opposite sides of the country were hired. Performance Structures Inc. (PSI), in Oakland, California, and MTH, in Villa Park, Illinois.

Construction of the shell structure was lead by PSI’s Ethan Silva, who had previous experience in creating similar structures for ships and art projects.

Silva said “we basically worked on that project, making those parts, for about three years. It was a major task. And a lot of that time was spent figuring out how to do it and working out the details; you know, just perfecting it.”

The unique shape of the structure posed various problems for the fabricators during the making of the outer plates. Among them was the daunting task of plasma cutting the 1/4 – 3/8 inch thick 316L steel plates. Some of the largest plates weighed as much as 1,500 pounds.

“The real challenge was to get the mammoth plates to the precise-enough curvature,” said Silva. “And that was done by very accurately forming and fabricating the rib-system framework for each plate. That way we could accurately define the shape of each plate.” The immensity of this project meant a three-dimensional rolled has to be designed and built specifically for the Cloud Gate plates.

Afterwards, welders flux-core stitch-welded the curved plates onto the rib-system. Silva explained his liking of the flux-core process, saying “Flux-core is really a wonderful way to create structural welds…it gives you a great-quality weld and it’s very production-oriented and it has a good appearance.” The support system waiting for the polished plates to be installed.

The work on the outer plates wasn’t done yet. For their picture-perfect appearance, the sheets were hand-ground and machine-milled to the thousandths-of-an-inch so they would all fit together perfectly. Fabricators used laser scanning equipment to check their dimensions, and then polished the plates and applied a protective film.

Once completed, the superstructure and plates were loaded onto semi-trucks and sent across the country to Chicago. A group of PSI workers were also sent to work with MTH staff in Chicago, who were now in charge of installing the sculpture and joining the pieces.

According to Lou Cerny, vice president of engineering and the project manager for MTH, the 30,000 pound substructure that supported the sculpture was one of the most difficult items they worked on.

“We started installing the truss system with two large fabricated 304 stainless steel O-shaped rings,” Cerny said. The photo above shows the structure’s rings help together by criss-crossing pipes. The frame between them is field-bolted and reinforced with GMAW and stick welding.

A suspension system was then used to assemble the shell over the substructure. Each of the 168 plates had its own hanging support system as it was put into place. It was set up this way to avoid over-stressing any joints on the system. Remarkably, the plates fit together on the structure perfectly.

“PSI did a tremendous job of fabricating the plates,” Cerny said. “I give them all of the credit for that, because in the end, it actually fit. The fit-up was excellent, which to me was amazing. We’re talking about, literally, thousandths of an inch. The plates came together with a closed edge.”

Silva said many people thought the work was done when the plates were put in. But the most important work of all had not been done – the welding of the plate seams. Plasma welding was done to provide the strength needed for the structure, and to avoid as much risk to the plates.

“The welds had to be full-penetration welds, but we had to weld from one side only—all from the exterior,” Cerny said. In order to achieve full weld penetration, workers used a custom-built chamber on the back-side of the plate. As the welder made his welds, the channel was flooded with inert gas and fed directly into the joint from the inside.

“We’re not talking about new technology—we’re talking about using the technology in a field condition under strange circumstances and modifying it to work,” Cerny said. “The heads were modified, cut at certain angles, and everything else was changed slightly. We did a lot of experimentation to get it to work, because it was all-position welding within the same run—meaning it’s right in front of you, vertically up, vertically down, and overhead. So you’re constantly adjusting your gas feed, your wire feed speed, how fast you’re traveling It’s something that the guys had to develop as they were working with it. There is no book that tells you that, unfortunately.” A tent surrounds Cloud Gate during construction.

With the welds completed, workers got started on the final phase of the project – polishing of the structure. The seam welds left many visible marks, which needed to be ground down using 60-grit zirconium paper on semiautomatic belt sanders. The next step called for the use of a special 400-grit ceramic sandpaper.

“It’s something you don’t really see in our industry,” said Cerny. “It’s usually for surgical instruments. But it works very well on stainless.”

With the support in place, the plates welded together, and the seams sanded down – the last step was applying a highly reflective polish. The substance used was a waxy substance called rouge

To achieve the gleaming, highly polished, reflective mirror finish, the finishers used a kind of jewelers’ polish, a waxy substance called a rouge. Three types of rouges contain three grades of abrasives.

“Everyone will tell you that if you skip a step, you have to go back,” said Cerny. “We had 24 or 25 people working at once just on the outside—we had to make sure all the steps were taken. We didn’t polish a 3-foot square all the way to mirror and then move over. We would do a certain step on large areas of the surface and then do the next step.”

After 5-plus years in the making, Cloud Gate was finally completed on August 28, 2005, and officially unveiled on May 15, 2006. The sculpture is seen by millions of people every year, all marveling at the odd shape and the mirror-like finish. It truly is a welding wonder brought to life for all to enjoy.

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