AND ON THIS BLISSFULLY balmy January day, a glimpse into the warm and bright mid-nineteenth century Madrid apartment belonging to interior designer, Luis Puerta, whose focus was on balance and harmony and naturalness and restraint, taking care to let nothing interrupt the flows of natural light. The existing columns and chimneys were retained, and the rich pine herringone flooring restored. With a mix of antiques, silk velvet and Belgian linens, it is a true study in refined elegance . . .