The engagement ring market is constantly evolving, as discerning consumers look for something different to set themselves apart from the crowd. For several years, the focus was on the vintage-style glamour of Edwardian and Victorian era rings – typically a statement diamond surrounded by a halo of small gems. Over the last few years though, we’ve seen a surge in demand for coloured gemstones. Part of this can undoubtedly be traced back to 2010, when Prince William presented Kate Middleton with the twelve carat blue sapphire ring that had previously belonged to his mother, Princess Diana. But even before this, blue sapphire had already been growing in popularity, as it…