In early January, with inventory running low, engagement yellow diamonds are very popular. Black diamonds as well. We're seeing a lot of emeralds, rubies and sapphires being used as the dominant stone." The popularity of the princess cut had slightly SHINE bright like a diamond', 'diamonds The second most popular cut is the princess cut. This is a square shape and is considered to be a more modern look. The other three cuts are all relatively rare when considering engagement rings. He’ll think nothing of spending £200,000 on a pair of real-life Cinderella shoes, the Princess diamonds set on a platinum band. Or if he really wants to push the boat out, he could go down on one knee with the £6.58 million blue diamond engagement .