ROCK TALK: These are busy days for Graff, which last Wednesday snapped up a rare, fancy, deep-blue diamond set in a Bulgari ring for a cool $9.5 million at Bonhams in London, and whose latest ad campaign launches in early May. The campaign, shot for the first time by the British fashion photographer David Slijper, features more than 5,000 diamonds — and a sprinkling of emeralds — set in 33 pieces of jewelry. The campaign will break in the June issues of British and French Vogue; British Harper’s Bazaar, Tatler and L’Officiel, and Town & Country.