New York City's public school system has a one-of-a-kind art collection, but not all of the artwork is in good shape. NY1's Education reporter Lindsey Christ filed her fourth report in the series "The Classroom Collection" on the the effort to identify and restore damaged pieces.

Hidden in a closet in the back of a classroom in Flatbush, Brooklyn, there is a priceless piece of art. Made by Tiffany Studios in 1919, it may be the most valuable artwork in the school system's entire collection.

It was originally in the Erasmus High School library, but at some point the library was turned into two classrooms. Two cloudy windows provide the only view of the piece, and some of what is still visible is covered in graffiti.

"There are pieces that are missing, there are pieces that are cracked, and the support structure itself is failing in sections. But it's a very important piece," says Public Art for Public Schools Director Tania Duvergne.

For decades, there was nobody in charge of the school system's unique art collection, but in 1989 an agency was created.

"Michelle Cohen was the founding director of the program and remained its director for the past 20 years. Under her stewardship, the very first directive was to inventory the existing collection, which had never been done," says Duvergne.

One of the discoveries was a massive mural in the Bayard Rustin school building that had been completely covered by layers of paint.

"There was a photograph indicating that there was originally an artwork in that space," says Duvergne.

The 1930s-era piece by Paul Lawler spans the entire library, telling the history of the textile industry. For the past five years, a team run by renowned conservator Luca Bonetti has been working to uncover it. It may be another 10 years before they finish.

"This was totally unknown territory," says Bonetti.

"It's a very lengthy and tedious process. We've had to fit that into our existing budget," says Duvergne.

Besides the paint, there are dozens of fixtures that need to be removed, as well as layers of dirt and grime. Eventually, the room needs lighting that does not block the mural. Each issue requires creative fixes.

"First see what the problem is, see what we want to do and find ways to do so," says Bonetti.

With older pieces, there are countless problems: from stained-glass carelessly cut to fit an air conditioner, to holes for telephone wires, to just general wear and tear.

"The school environment is a very tough environment for artwork to exist in," says Duvergne.

With new commissions, durability is key. As for older pieces, they are slowly chipping away at restoration, hoping students notice the priceless art in the closet.