<P> The terminal building primarily uses granite, so the building emits radiation . People who work full - time in the station receive an average dose of 525 mrem / year, more than permitted in nuclear power facilities . </P> <P> Midtown TDR Ventures has owned the station since 2006, when Argent Ventures transferred ownership of the station . The Metropolitan Transportation Authority, the state agency that is the parent of Metro - North, holds a lease until 2274 . </P> <P> The Main Concourse is the center of Grand Central . At 275 ft (84 m) long by 120 ft (37 m) wide by 125 ft (38 m) high, the cavernous Main Concourse is usually filled with bustling crowds. and is often used as a meeting place . The ticket booths are here, although many now stand unused or have been repurposed since the introduction of ticket vending machines . The large American flag was hung in Grand Central Terminal a few days after the September 11 attacks on the World Trade Center . The main information booth is in the center of the concourse . The four - faced brass clock on top of the information booth, perhaps the most recognizable icon of Grand Central, was designed by Henry Edward Bedford and cast in Waterbury, Connecticut . Each of the four clock faces is made from opalescent glass (now often called opal glass or milk glass), though urban legend has it that the faces are made of opal and that Sotheby's and Christie's have estimated their value to be between $10 million and $20 million . A 1954 New York Times article on the restoration of the clock notes that "Each of the glass faces was twenty - four inches in diameter ..." Within the marble and brass pagoda lies a "secret" door that conceals a spiral staircase leading to the lower - level information booth . </P> <P> Outside the station, the 13 - foot (4.0 m) clock in front of the Grand Central façade facing 42nd Street contains the world's largest example of Tiffany glass . It is surrounded by the Glory of Commerce sculptural group, which includes representations of Minerva, Hercules, and Mercury . The sculptures were designed by French sculptor Jules - Felix Coutan and carved by the John Donnelly Company . At its unveiling in 1914, the 48 - foot - high (15 m) trio was considered the largest sculptural group in the world . </P>

Who made the clock in grand central station