Lowengard was a Parisian firm of art dealers headed by Jules Lowengard, which had many American clients. Jules' wife Esther was Joseph Duveen's sister. Their son Armand Lowengard joined and eventually became co-owner of the Duveen firm. Peter A.B. Widener purchased a sixteenth-century enameled copper plaque (now in the NGA) from Charles Lowengard in 1908, the same year that Jules Lowengard died.