NYTIMES – A granite-faced townhouse in the Back Bay neighbourhood of Boston was designed more than 100 years ago by artist Louis Comfort Tiffany and is seen today as the most comprehensive surviving example of his residential vision.

Its pale facade, with mosaic panels set in limestone and a stained-glass window over copper-clad double doors, is one of only two exteriors known to have been designed by Tiffany and the only one that remains intact.

The interior, featuring an oval staircase and an entrance with white marble wainscoting and mosaic stair risers, is equally striking.

For decades, the building, known as the Ayer Mansion, has been owned by non-profit organisations connected to Roman Catholic group Opus Dei and has functioned as part of a cultural centre and a residence for women attending nearby colleges. During that time, its doors have periodically been opened to the public for tours, lectures and concerts.

All that could soon change.

The mansion was recently listed for sale – along with an adjoining building – with a US$22.5 million (S$30 million) asking price. That worries some people who have worked for years to restore what they regard as a crucial monument to Tiffany’s genius.

Ms Marie Oates, a spokesman for the Trimount Foundation, which owns the mansion and the adjoining building that make up the residence and cultural centre, said the listing was for both properties and was prompted by the coronavirus pandemic-induced fall in student fees that help fund the buildings’ operation.

“We would like to give priority to a buyer or an offer where there’s going to be an interest in preserving what is a national treasure,” she said. “If we can find a buyer who is going to allow public access, that would be awesome; we would be thrilled.”

Ms Alice Cooney Frelinghuysen, an expert on Tiffany, said the Ayer house was remarkable largely because nearly all of its original elements have been preserved.

These included the modernist entrance hall, dramatic stairway, gold mosaic ceilings, Favrile glass vases and a trompe l’oeil temple on a stair landing that combine to form a unified ensemble.

The mansion is an “extraordinarily important surviving interior by Louis Tiffany”, she said. “It was all conceived as an entire work of art.” The mansion was built between 1899 and 1902 for businessman and art collector Frederick Ayer, according to the Campaign for the Ayer Mansion.

Since 1964, it has been owned at different periods by two separate non-profit organisations associated with Opus Dei, an influential group historically connected to right-wing causes that was founded on the premise that ordinary life and daily work are paths to sanctity and service to society.

The building has been used during that entire time by a third non-profit organisation, the Bayridge Residence and Cultural Centre. It began a restoration effort in 1997, first hiring an architecture firm to study the mansion and prepare a preservation plan. Since 1998, the restoration has been organised by the Campaign for the Ayer Mansion and a similarly named predecessor group, which obtained grants from the City of Boston, the Massachusetts Historical Commission and the federal Save America’s Treasures programme, as well as from private foundations and donors.

With the cooperation of Trimount and Bayridge, the Ayer Mansion campaign has undertaken close to US$3 million worth of interior and exterior works, including restoration of mosaic panels on the facade and repair of stained-glass screens in the mansion’s library.

It also restored a 6m-long Tiffany laylight above a set of marble stairs, using existing glass and replacing missing pieces with rare surviving glass from the Neustadt Collection of Tiffany Glass.