This spacious duplex for an antiques collector and his family in an Upper East Side landmark building both modernizes and highlights the interior’s period features. To brighten the rooms, existing dark wood paneling was restored and painted a warm, pale shade. Large travertine tiles replaced the parquet floors, while custom millwork was installed throughout and designed around original fixtures, including kitchen sinks and bathroom vanities. Downstairs, the adjoining living and dining spaces were opened up to showcase the collector’s impressive collection of Asian artifacts for business clients.