Last week, I asked whether anyone knew the status of Anish Kapoor’s silverblob of a sculpture at 56 Leonard. Handily, someone forwarded a recent communication from the fabricator, Performance Structures, Inc., to the developer:

In response to your request for information to gain a better understanding of the progress on the sculpture project, here is a brief description of some of the challenges and achievements.

The 56 Leonard Street sculpture, designed by Anish Kapoor, is soon to be one of the great landmark pieces of public art in New York City, and internationally. It is a continuation and evolution of the artist’s monumental public artwork, most notably Cloud Gate in Chicago, completed in 2005. Like Cloud Gate, the Leonard Street sculpture is a large mirror finished smooth form that will reflect the surrounding cityscape.

Building Cloud Gate presented us with many challenges. We needed to precision-form stainless steel plates, attach them to precisely made supporting frame works, very accurately machine these components, and then polish them to a mirror finish. Each plate needed to be the exact shape required, so that when all were assembled the results would create a perfect sculptural form.

The Leonard Street sculpture requires equivalent accuracy and precision, but with an added component. Cloud Gate was assembled in Chicago from the finished plate sections and support framework, built at our facility, and then all the joining seams were welded together on site. After the seams were welded, they all needed to be ground down, and the seam zones sanded and polished to match the rest of the plate surfaces. This on-site seam welding was very laborious and extremely costly. In addition, the welding process, by its very nature due to weld shrinkage, distorts the adjacent metal that is being welded. This distortion in turn necessitates a very time consuming and tedious smoothing process, prior to the polishing, in order to make the final shape at the seams perfectly blend into the whole surface.

The welding and fairing process described above added a huge amount of time to the installation process, and more than doubled the cost of the sculpture. In order to make the Leonard Street sculpture installation more expeditious, and to save costs, it was decided to build the precision components such that they could be tightly fit together, with the seams thereby becoming nearly invisible hair line cracks. This concept was successfully tested in a sample piece produced by us, and presented to the Artist for his approval prior to beginning the project.

We have fabricated plate sections to create vertical segments of the sculpture, or “slices.” Pairs of these slices are then joined by bolts and ground smooth and polished as a unit, across the joining seam. Once a pair of slices have been finished in this way, they are separated and each slice is joined with another slice that fits on the other side, and then that new joining seam is ground and polished. In this way all of the slice sections will have been ground and polished across all of the seams, so that when they are all joined together they will form a single smooth sculptural form.

Our challenges in the production of the component parts of this project, different than Cloud Gate, have been twofold. First, to machine the plate components to such accuracy that when two are welded together to form a slice, the joining edges are perfectly straight so that mating slices will fit tightly together without any gaps. Second, to work out the exact joining mechanism between the very large slices such that during the finishing process, and subsequent reassembly, the seam remains no more than a hairline crack. The development and refinement of this complicated process has caused delays in the building of this sculpture, but the slices are now being produced and joined with the results the project requires.

Another significant difference between the Leonard Street sculpture and Cloud Gate is the suspension system. In the case of Cloud Gate, the sculpture is supported by a large base frame bolted to the plaza, which also is comprised of two large ring structures. The shell of the sculpture is suspended by means of a series of spring connectors joining the shell framing to the support rings. The Leonard Street sculpture has a different support mechanism. Instead of a single large support frame, each slice has its individual support frame. The support frames for the bottom slices are each bolted to the plaza, and the slices themselves are suspended by means of cables. When completed, the entire sculpture will be suspended with a system of cables and spring members so that it will be able to move slightly with changes of temperature and wind and snow loads. All of the cables will need to be properly tensioned during the installation process.

Currently we are in the process of producing the last section of slices. We have begun assembly of the completed slices at our facility. Once all the slices and the “crown” components have been fabricated and polished we will be able to totally assemble the sculpture for review by the Artist at our facility, prior to shipping the components to New York for final installation.

I believe that the sophisticated curvilinear shape of this sculpture will create a truly unique and momentous entry to 56 Leonard Street and it will become an icon of Tribeca.