Christie’s auction house reported its highest-ever sales total for the first-half, topping of $4 billion during the first six months of this year and highlighting the continued strength of the global art market. Total sales were up 35 percent in the first six months of 2018, according to Christie’s, which is privately held. More than three quarters of the gain came from the sale of the David and Peggy Rockefeller art collection, which totaled $835 million and set a new record for a single collection.