Sandro Botticelli's Portrait of a Young Man Holding a Roundel (around 1480) is set to break a record for the Old Master painter PHOTO: JULIAN CASSADY PHOTOGRAPHY; COURTESY OF SOTHEBY’S Sotheby’s sale this month of an arresting Botticelli portrait, owned by the late real estate billionaire Sheldon Solow, has been heavily publicised. Yet, while Portrait of a Young Man Holding a Roundel (around 1480) is accompanied by the obligatory paraphernalia of X-ray and infra-red images, its many mysteries continue to confound trade and scholars alike. And the estimate, in excess of $80m, has no precedent: works fully attributed to Botticelli rarely come up and the auction record for a painting by the artist is just $10.4m, set in 2013 by the “Rockefeller Madonna” (or