Up-close look of the ceiling at the Painted Hall in London Visitors can now see London's largest ceiling up close.

 LONDON -- London’s largest painted ceiling is undergoing a major transformation.

The Painted Hall at the Old Royal Naval College, part of Maritime Greenwich, a UNESCO World Heritage Site, is being conserved for the first time since the 1950s. This means that visitors can get closer to the ceiling of the Painted Hall than ever before -- and that even conservators who know the paintings very well are discovering the details of the artwork.

“It’s a pretty amazing and weird experience,” Will Palin, director of conservation at the Old Royal Naval College, told ABC News. “When the scaffolding first went up it was very disorientating because, of course, they were never meant to be seen this close. ... So you get these moments where you look up and you see these very powerful, brilliant moments of baroque painting and you also get to see the detailed brushwork of the artist....”

One of the details in the painted ceiling that Palin had never seen before is a signature on Queen Mary’s chest – placed there by one of the conservators who worked on the ceiling back in the 1700s.

“You would expect those responsible for restoring the surface over the ages to respect the painting and not leave a bit of graffiti -- and if they are leaving a bit of graffiti, not to leave it on the queen’s bosom. That’s the most disrespectful,” said Palin.

Back in the 1700s, the Old Royal Naval College was a place of refuge for retired and injured sailors who had served in the Navy. English painter James Thornhill created the Painted Hall in the baroque Italian tradition. Some compare the room to Rome’s Sistine Chapel.

“It was designed originally as a dining hall for the sailors who lived here,” Kay Potter, a volunteer guide, said as she gave ABC News a tour of the Painted Hall. “But in fact, it was decorated shortly after it opened. While it was being painted they were moved downstairs. And when it finished, they didn’t really want to move back because it was too grand for them and they were more comfortable staying downstairs.”

Instead, the Painted Hall turned into a tourist attraction and the retired sailors were the tour guides.

The conservation project is due to last two years -- once the work is done, the colors of the paintings will be much brighter. Dirt will be cleaned away while damage, such as whitening and loss of paint, will be fixed.