RAPAPORT... Christie's will auction a 28.86-carat diamond ring at its next Jewels Online sale, the largest D-color diamond ever offered online, the auction house said Wednesday.The emerald-cut, VVS1-clarity, type IIa stone is also the highest-priced lot ever offered for sale online at Christie's. The piece, which has a presale estimate of $1 million to $2 million, is set to go under the hammer on June 30.Due to the increased levels of online participation, Christie's has begun adding higher-value items to its sales, and will also offer an online jewelry sale every month, it said. The auction house has launched a virtual private-sales viewing room, which allows buyers to examine available items remotely in close detail and confer directly with specialists."This year has presented unprecedented circumstances, enabling Christie's new opportunities through our enhanced digital platform," said Rahul Kadakia, international head of jewelry at Christie's. "Year over year, we have seen an increase in online participation and the value threshold for transacting online."After the June sale, Christie's will hold online jewelry sales from July 22 to August 6 and from August 12 to 26. The auction house will announce dates for its Luxury Week in Geneva, New York and London in the coming weeks.Image: The 28.86-carat diamond. (Christie's)