The giant marble lions that have stood guard outside of the New York Public Library's main branch in Midtown Manhattan will undergo their once-a-decade-or-so restoration this week. 

Dubbed Patience and Fortitude, the lions have looked out over Fifth Avenue since 1911. But a combination of vehicle exhaust, the elements and visitors eager to climb the iconic duo have taken their toll. So this week, the library will haul the statues off, scrub them clean and restore them.

Iris Weinshall is the library's Chief Operating Officer. She said the lions are made of a porous pink Tennessee marble, which makes them especially vulnerable to fluctuations in the weather. 

“If it's cold and snowy one day, and then it warms up the next, and then it’s cold again, the marble expands and contracts and this causes cracks,” she said. 

WJE Engineers and Architects is in charge of the lions’ clean up. It's the same company that led the restoration of the ceiling in the Rose Reading room a few years ago. 

For the first time, the company will be using lasers to scrub the lions clean. The light waves will scrape off anything on the pair's marble surface.

After that, the workers will fill the cracks and take care of other repairs. The whole process should take about six weeks. 

Susan Larkin wrote the book "Top Cats: The Life and Times of the New York Public Library Lions". She said the level of doting care given to the pair now might have surprised their sculptor, Edward Clark Potter. During his lifetime the lions were actually quite unpopular. 

"The public and the press, apparently, was very put off by the many construction delays and cost overruns," Larkin said. "I guess in a sense, the lions first roles as symbols of the library began with them being scapegoats."

But eventually, the lions were adopted as symbols of the city. To Larkin, that reversal is very understandable. 

"The lions are kind of lovable." she laughed.