When the restoration is complete, a completely gilded Diana never seen in Philadelphia will glow amid new lighting.
Gone will be the dulled and corroded copper surface, gone the shadows settled throughout the stair hall.
"We are going to return this masterpiece to its original glory," museum director and chief executive Timothy Rub said Thursday.
Diana, said Andrew Lins, chair of the museum's conservation department, "was once absolutely brilliant."
When originally unveiled in New York, noted Rub, Diana was "covered in gold leaf and gleaming in the sun."
Kathleen Foster, the museum's senior curator of American art, said "she glowed in the daytime" from atop the Stanford White-designed Garden, a "pleasure palace" at 26th Street and Madison Avenue.
And when the sun went down, New York's first bank of floodlights on the Garden's rooftop switched on, illuminating Diana.
"At night she was a beacon for the whole city," Foster said. "You could see her from New Jersey and Connecticut."
Looking out across New York from a height of 347 feet, Diana was the highest point in the city.
But the Garden, a massive entertainment complex with an amphitheater that could seat 12,000 people, three theaters, a bevy of bars and restaurants, and a lavish roof garden, gradually sank into bankruptcy.
The building was demolished in 1925 and Diana was placed in storage, awaiting completion of a new tower promised by New York University. But NYU could not raise the money to build.
In 1932, the Art Museum's dynamic young director, Fiske Kimball, persuaded the New York Life Insurance Co., Diana's owner, to give the sculpture to the museum in Philadelphia.
She was installed in 1932 at the top of the stairwell, the original gilding all but gone after 30 years in the Manhattan sky.
Diana "has not moved since," Rub said.
Kimball did not give a thought to regilding the statue as the Great Depression deepened. Cost put the matter outside consideration.
Nor did New York seek to retrieve its lost masterpiece for more than three decades, said Foster. John V. Lindsay, New York's mayor in the 1960s, tried to persuade Philadelphia city officials to return the sculpture.
He was rebuffed. New York officials have not tried to make their case since.
When the actual regilding process commences, probably in August, the 13-foot sculpture will be enclosed and a webcam will be installed so that viewers can follow the restoration work.
In the stair hall, lighting will be redesigned to augment the sculpture's brilliance. It will transform the monumental space along with the sculpture, said museum officials.
Lins, the conservator, said the fragile sculpture will first be extensively examined using a variety of techniques.
Diana's surface is formed by sheets of beaten copper. The statue is hollow and light - capable of turning in the wind like any weathervane.
The sculpture is braced from within by an armature.
At some point during or after its removal from atop the doomed Garden (where it looked out over the roof garden the night White famously was shot to death by Harry K. Thaw in 1906), Diana was damaged, said Lins.
The damage was ostensibly repaired, but Lins wants "to check and double check" the interior workings of the piece.
There are still some flecks of the original gold leaf here and there about the body, he added. Those will be analyzed and gilding will be created to match the original.
The entire project, which officials said would run about $200,000, is being funded by Bank of America as part of an international conservation initiative. Thomas C. Woodward, the bank's Pennsylvania president, said 24 conservation projects in 16 countries would receive bank funding in 2013.
Contact Stephan Salisbury at 215-854-5594, firstname.lastname@example.org, or @SPSalisbury on Twitter.