Antique, Art Deco, 18ct Rose Gold, French, Natural Colour-Change Sapphire and Diamond Cluster Ring

Colour-change sapphire and diamond ring, 20th century. This unheated Sri Lankan sapphire appears a subtle cornflower blue in daylight, and a soft violet in incandescent light. The reason for this unusual phenomenon is the presence of Chromium in the stone, which gives the stone its violet hue, and interacts with different colours of light to change the shade of the stone. The presence of Chromium also means that, unusually for a blue sapphire, it also fluoresces red. Under  The design is a classic cluster with touches of Edwardian inspiration, particularly in the millegrained settings of the diamonds, making it a beautiful and timeless choice for an engagement ring.