Natural LUSTER

Take a trip to the Natural History Museum of Los Angeles County and you’re bound to encounter some impressive bone structures. Popular tenants include the Tyrannosaurus rex and a complete cast of the long-necked Mamenchisaurus. But the biggest dinosaur is perhaps the building itself -- a hulking, fossilized fortress from a bygone era.

A three-year, $84-million renovation of the famed skeletons’ 1913 home in Exposition Park aims to change that, but the project is proving to be particularly challenging. The museum says that the original architects left behind only basic blueprints of the building, and in some cases, entire designs have been lost.

As a result, the museum is approaching the project as if it were one of its own archaeological expeditions, ready to uncover all sorts of surprises -- good and bad -- along the way.

“It’s the biggest undertaking in our history,” says Jane Pisano, president and director of the museum. “Going in, we knew it would be difficult and that we would probably encounter things we didn’t know about.”

That intuition proved abundantly true during the renovation’s just-completed first phase, which centered on one of the building’s treasures: the fragile stained-glass skylight that crowns the museum’s 57-foot-high rotunda. Designed by the Judson Studios in Los Angeles, the skylight is one of the city’s few remaining large-scale works that date from the American Art Glass movement of the early 20th century. In recent years, the skylight’s bright colors and eclectic shapes have been dulled and clouded over, the victims of time and neglect.

“The last time anyone had touched the glass was more than 15 years ago, so anything was possible,” says David Judson, president of the Judson Studios -- and great-grandson of the skylight’s designer -- who was hired last fall to oversee the skylight’s restoration.

A thick layer of dirt coated the exterior of the glass when he climbed up for his initial visit. He also noticed generous amounts of pigeon droppings -- an unhappy find for more than aesthetic reasons. The ammonia in bird feces can weaken the linseed oil-based cement that helps keep the approximately 3,200 pounds of glass in place.

Perhaps more worrisome, crews soon discovered that the 16 curved panels that make up the 24-foot-wide circular skylight were sagging significantly. The crews cleaned each panel, stabilized cracks with a silicon compound and replaced some of the damaged pieces of opalescent glass, repainting and refiring one chunk of streaking amber at the Judson Studios in Highland Park. The panels were rehung from their steel beam supports with double the original number of cables.

A recent tour of the skylight revealed a startling brilliance when compared with photos of the unrestored glass. Colors pop out with fauvist intensity while intricate patterns have come into sharper focus.

“When you walk in, your eyes are taken up and there’s kind of an exclamation point,” says Judson. “The glass acts as a crescendo of what the space is.”

Ongoing restoration digs deep

The stained-glass repairs are just the beginning of the multiyear overhaul. The museum has hired Cordell Corp., a project management company based in Nevada City, Calif., to completely refurbish the building’s infrastructure, work that began last year and is expected to end in 2010, when the space is to reopen.

The three-volume design document guiding the renovation is nearly 6 inches thick -- mammoth by comparison with the original 1913 design by the architecture firm Hudson & Munsell, which was only 24 pages.

“Back then, the architects laid out their general vision and let the builders figure out a lot of the details,” says Don Webb, the lead construction manager. “That would never happen today.”

Some of Cordell’s discoveries have greatly compounded the workload. Inspections revealed cracks in the rotunda’s outer dome as a result of shifting in the underlying concrete. That ultimately meant that the museum would have to remove the putty in between the individual ceramic tiles that sit on top of the concrete -- some 1,866,000 of them on the main dome -- and then inject an epoxy sealant between each of the 1-inch-by-1-inch pieces.

Crews also learned that all of the steel connections in the building are riveted together, not welded as is customary today. (Welding only came into vogue in the 1930s.) The building doesn’t contain any washers, which are commonly used by crews to fill in gaps and compensate for inaccuracies. The museum decided it would maintain the integrity of the design and stick use no washers in the restoration.

Other discoveries have proven less burdensome. The staircases leading up to the second floors of the north and south galleries, which had been covered by a gray carpet, were found to be made of battleship linoleum, an expensive material often found in old sea vessels, cars and floors. Workers will polish the linoleum to restore its original brilliance. Elsewhere, the museum is finding mosaics and marble walls that had been previously concealed.

“We’re in a constant process of discovery,” says Karen Wise, executive project manager at the museum. “It’s tremendously exciting. When you work on a building like this, you have to look at every square inch of it, and you’re always finding new things.”

Actuality and intention

Among the more decorative aspects of the restoration is a 6-foot statue of an eagle that originally stood above the east entrance but was destroyed in an earthquake about five years after the museum opened.

Researchers have only been able to find one black-and-white photograph of the eagle, and it differs significantly from the architects’ blueprints: The wings and feet are in different positions, and the sphere on which the eagle stands has a sash in the drawing but not in the photograph.

For the construction team, the debate is whether to sculpt the eagle in the way that was originally intended by the architects or to base it on what was built. (When this story went to press, the museum was leaning toward reconstructing what was built as closely as possible. The eagle is expected to be completed sometime this fall.)

Much of the other work, which involves seismic retrofitting, will be invisible to visitors when the building reopens in a little more than two years. Crews have drilled 6-inch-wide vertical holes through the walls, starting at the roof and going down through the foundation, then placed a steel rod in each hole and filled the cavity with an epoxy-like polymer.

It’s an unconventional way to stabilize a building this old, according to the museum, but the typical method of erecting a steel skeleton would have altered the architecture of the building and decreased the amount of exhibition space.

In the rotunda, crews are filling 155 light sockets with LED (light emitting diode) bulbs, which give off less heat than either incandescent or fluorescent lights. Keeping the rotunda cool is important since heat can cause the lead in the skylight to soften. There’s another advantage to the LED switch: The museum will have to replace the lights only about once every 10 years.

A new lighting system above the skylight will illuminate the rotunda in the evenings, showcasing the stained glass, which has not been lighted at night for decades (though workers discovered an abandoned system of incandescent bulbs and glass diffusers). It will also show off the building in a way never before seen, Webb says. Some of the beneficiaries of the improved illumination will be a new fossil hall opening in 2010. (Designs for new exhibits are to be revealed later this year.)

“We don’t want the building to compete with the exhibits,” Webb says, “but we’ve found some elements that we think are worth being part of the story.”

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david.ng@latimes.com