Breathtaking stained glass windows of Gilded Age mausoleums are seen for first time in a CENTURY, thanks to conservation project which revealed undiscovered Tiffany masterpieces

Hidden in the mausoleums of one of New York's cemeteries sits a king's ransom of breathtaking stained glass - commissioned by the city's rich and powerful more than a century ago.

Officials at Woodlawn Cemetery first stumbled on the glasswork late last year, in a Gilded Age temple erected for a New York merchant and son of a Spanish general.

During an audit of the colorful windows, experts discovered a variety none had ever seen before - despite being seasoned officials on the subject.

They are now in the midst of an unprecedented survey that will see them peruse about 1,200 windows in the cemetery's 1,300 private, free-standing mausoleums, and reenter Gilded Age-era temples meant for the very wealthy.

Some have been sealed as far back as 1878, creating unique conditions experts in an interview compared to a 'microclimate. '

To gain entry, a local company adapted antique keys built by mausoleum makers in the late 19th century,

Gilded Age tycoon John H Harbeck's mausoleum in Woodlawn Cemetery, NYC, is constructed from austere gray stone - but it contains a very colorful secret 

Visitors to the final resting place of the warehouse and railroad tycoon, who died in 1910, are greeted with a stunning stained glass window - one of hundreds at the cemetery, many of which have lain undiscovered for more than a century

The window in all its glory, complete with an image of Jesus surrounded by followers 

This window is believed to be an unsigned work by iconic stained glass artist Louis C. Tiffany. It was installed in the mausoleum of JG Payntar in 1899 and only recently uncovered during a survey of the cemetery's glasswork 

A mausoleum at Woodlawn whose owner and construction date has not been shared is filled with glorious amber and blue light as the sun pours through its richly-colored glass 

A gorgeous cross and orb sits in the mausoleum of Jose Maria Munoz, a merchant born in Panama who made his fortune in New York. Munoz was the son of a Spanish general, with stained glass artists who recently discovered this window marveling at the 3D effect of the spherical orb, which was previously-unheard of for the time period 

An all-star cast of stained-glass experts is carrying out the reentries, which will include a condition assessment, photographic documentation and archival research on every stained-glass window in Woodlawn's collection.

So far, it has yielded some surprising results - like the previously undiscovered window found behind a stone sarcophagus over the summer.

Already half completed, it has also resulted in the identification of several unsigned works from American artist Louis Comfort Tiffany, whose glasswork revolutionized the field through his use milky, brilliant opalescent glass.

Also made famous by Tiffany contemporary John La Farge, the material boasts 'an internal glow and a milky translucency that captures light and amplifies color', said Lindsy R. Parrott, on of the experts carrying out the study.

Part of the impressive roster of stained-glass aficionados conducting the study, she's the executive director and curator of a major collection of stained glass by master artist Tiffany at The Neustadt Gallery at the Queens Museum.

A delightful spring scene featuring daffodils and bluebells in front of a calm body of water  

While many windows focused on the natural world, others depicted scenes of Christianity, including this heavenly image of Jesus flanked by two angels 

She is joined by Brianne Van Vorst, a conservator with a New Jersey art restoration service that specialized in stained glass, and is also an authority on the subject.

She sat down with DailyMail.com this week to speak about the team-of-five's quest to traverse the long-sealed burial vaults to see what's inside.

Van Vorst explained that so far, they've documented around 600 of the stained glass windows and that the artistic provenance of 100 of them is known.  

'It feels totally like Indiana Jones,' Alice Cooney Frelinghuysen, a curator of American decorative arts at the Met, told the New York Times.

Recalling the countless clammy chambers she, Van Vorst, Parrott, and fellow conservators Edward Sperry and Drew Anderson have entered since last year, she added: 'Sometimes we walk in and there's that feel of damp, mold and leaves.

'And [then] you see an incredible window you've never seen before.'

Anderson, meanwhile, is a stained-glass conservator at the Metropolitan Museum of Art, but has still left in awe by some of discoveries - including a three-dimensional design element from the flat plane of the window found over the summer.

'I've never seen anything like this before, anywhere,' he said of the jeweled blue-glass orb protruding from 1890s-era window, whose creator remains unknown.

Another of the heavenly stained glass windows that has recently been documented at Woodlawn Cemetery 

Stained glass conservation expert Brianne Van Vorst (pictured left in red gloves) shows visitors one of the many beautiful stained glass windows on display at Woodlawn

Glass experts Lindsy Parrott (left) and Alice Cooney Frelinghuysen (right) have also helped identify the undiscovered gems, with Cooney Frelinghuysen saying their work has felt as exciting as an Indiana Jones movie 

Van Vorst, Parrott and Cooney Frelinghuysen are pictured with fellow glass expert Drew Anderson outside a Woodlawn Cemetery mausoleum  

A striking stained glass window depicting an angel is among those hidden away in Woodlawn

A bucolic scene is depicted in this stained glass window, with the tycoon who commissioned it possibly seeking to create a vision of heaven 

Another newly-discovered Tiffany window at Woodlawn. The window's creator was identified by experts Alice Cooney Frelinghuysen and Lindsy Parrot 

A gorgeous 1897 stained glass version of painter Paul Thumann's The Three Fates was also uncovered in Woodlawn 

A blazing Tiffany sunset created for a mausoleum that was built in 1912

Another Tiffany window dating back to 1900. While the faded colors have their own beauty, conservationists can bring some damaged windows back to life by inserting a panel of glass behind the original complete with the details that have been lost. It offers a truer picture of what the stained glass looked like originally, without altering it

Stained glass expert Brianne Van Vorst had a close encounter with a bee hive while documenting this beautiful window in a Woodlawn Mausoleum 

Other windows focused on the beauty of nature, with this glass work depicting flowers in bloom against a pale pink background