640 Fifth Ave.

To prepare for a project, glass artist Christopher Cosma goes to the installation site to learn its history and to create a foundation for his piece.

“From an artist’s point of view, you have to collect information of the past, present and future,” says Cosma, co-owner of the studio Amses Cosma Inc. of Brooklyn. “You learn the experience of that building.”

Cosma went through this same process with the crystal bas relief sculpture he created for the lobby of 640 Fifth Ave. in New York. He created a lobby installation for the 1930s-era building that was undergoing a major renovation designed by Kohn Pederson Fox of New York City.

Situated on the north side of Rockefeller Center, the busy office lobby is alive with constant activity from the businessmen and women who flow in and out every weekday.

“The building was open when I started work on this project,” Cosma says. “So, I spent time watching people come in and out. … I watched the constant movement. The first thing you see when you come in, the anchor thought of the building, is all the flow of tenants.”

Cosma expressed this movement in the 50-foot-by-10-foot sculpture that lines the lobby wall opposite the building’s six elevators. He created “arcs of motion” in the 63 panels of crystal glass, using ovals, waves and semicircles that seem to rise out of the glass and flow from panel to panel.

Cosma initially created maquettes and detailed drawings of the sculpture. The first full-scale sculpture was done in clay over Styrofoam mounted on medium density outer board plywood.

A computer controlled hot wire greatly simplified this stage in the process, as Cosma can quickly work in coordinates to make perfect arcs and ovals in the foam that previously could have taken days. He formed the finalized design in clay atop the foam, meticulously working out textures and other details of the piece.

More textures created a whiter appearance, while smooth and polished areas allow more light through. Cosma chose to use various textures throughout the piece to provide lightness and to avoid fingerprint smudges. From that stage, he created the permanent archival mold in fiberglass reinforced plaster.

In the next step, Cosma filled the mold with rubber. After the rubber duplicate was cured and removed, he created a refractory mold that was used with the actual crystal pieces for the final work. This mold was broken and destroyed when the finished crystal sculpture was extracted.640 Fifth Ave.

Cosma used F7 optical crystal from Schott North America in Duryea, Pa., because of its high index of refractivity.
The raw crystal arrived in extruded strips about 21⁄2 inches by 10 inches by 30 inches. Cosma carefully broke the glass into a variety of sizes to cast in the clay mold.

The size of the broken crystal pieces in the mold affected the clarity of the sculpture in the untextured, polished portions. The pieces created web-like patterns and bubbles that Cosma manipulated to create movement in the interior of the glass.
“It’s very important to have a good understanding of how the glass melts and how it will affect the inner composition,” Cosma says. “Something with webs or bubbles can create layering in the glass, showing depth.”

Cosma used a bell kiln to melt and anneal the glass in the molds. To melt the glass, the kiln temperature slowly rose to 1,575 degrees Fahrenheit and held for at least six hours at the melting temperature. The temperature gradually lowered for about a week, falling to 860 degrees when the glass was annealed.

The pieces come out of the kiln in a rough form. Cosma and his team sometimes spent a week polishing the crystal to its finished look.

“Polishing the glass is done with a variety of electric and pneumatic tools with silicon carbide grits, diamond pads, felt pads with pumice and cerium oxide,” Cosma says. “It is highly skilled work and very time consuming. Each form must be polished on all the edges to let the light pass through from the lighting above, and to match the panel next to it, with all the forms flowing in terms of polish and texture.”

For the glass pieces in the 640 building to not break because of the vast differential in thickness, they must be at least 11⁄2 inches thick. The thickness of the glass on the building ranges from about 11⁄2 inches to 8 inches.

Each of the 63 panels weighs between 200 and 300 pounds, and the total sculpture more than 9 tons, Cosma says.
To support the weight of the structure, Cosma built a steel grid of 6-by-6 inch steel tubing that ties into the building. He attached two pieces of plywood with sheet steel sandwiched between the plywood, and then attached the 3-inch stainless steel frames, custom fabricated at Cosma’s studio. The individual pieces of the sculpture fit into the frames.

A three-person team installed each panel, lifting and guiding the panels one by one with a manual lifter, Cosma says.
“We are extremely careful at this stage,” Cosma says. “You really can’t have things break, because we’ve put so much time in at this point.”

Lighting of glass sculptures also is critical, Cosma says. In the 640 building, the installation needed to light up the windowless and dark granite lobby area. The sculpture is lit from the front, and behind the glass, Cosma installed 1⁄4-inch mirror to brighten it further.

The project took about a year, with six months dedicated to casting, about four months used for sculpting and the rest for installation. Vornado Realty Trust in New York City commissioned the installation.