Interior designer Michael S. Smith shapes the decor of a New York City apartment to make the most of the museum-quality art collection on view. A few months ago, when the designer Michael S. Smith was flipping through a book about Maison Jansen, the renowned 20th-century Paris-based decorators, he came upon a familiar painting. In the pale-blue dining room of a magnificent Fifth Avenue residence designed in 1959 for Charles Allen Jr., founder of the investment firm Allen & Co., hung a Monet canvas Smith had recently installed in an apartment several blocks away on Manhattan's East River. "I couldn't believe it," Smith says. "Here were two chapters in the history of this one painting."