A new exhibition at the Carlton Hobbs gallery, On Tops: Table Tops from the 2nd Century to the 19th Century, offers a wonderful assortment of tables with some of the most precious and artistic tops ever assembled. Emphasizing extraordinary techniques and materials—from pietra dura (inlay of fine or hardstone) to micromosaic to scagliola (plasterwork in imitation of ornamental stone)—the inventiveness …