Diamond and jewelry stores started moving to 47th Street just after World War II. All those newly married future parents of "baby boomers" had to shop somewhere!
23 October 1952, New York Times, Classifieds, pg. 56, col. 4:
47TH, 54 W (Diamond District)
13 March 1955, New York Times, pg. R1:
IS SPREADING OUT
47th Street Block Between
5th and 6th Avenues Is
Drawing New Tenants
The jewelry district is expanding on West Forty-seventh Street.
The Fifth Avenue Jewelers Exchange, sponsored by Julius Furst, was opened on Dec. 16, 1948. It replaced two old brownstone houses on the south side of the street.