People born in September have a beautiful birthstone, the sapphire. Sapphires belong to the corundum family of gemstones, along with rubies. The difference between sapphires and rubies is determined by colour as they are both composed of aluminium oxide. The addition of chromium to the aluminium oxide results in a ruby while the addition of iron and titanium to the aluminium oxide results in a blue sapphire.
Sapphires come in many colours including yellow, pink, colourless (or white), orange, green and black although the best known colour is blue. When referring to sapphires that are not blue, the correct description is a pink sapphire or a yellow sapphire, but it is understood that when a stone is described as being a sapphire, it is a blue stone.
How blue should a blue sapphire be? For instance, there is no doubt that all of the sapphires in the photographs in this post are blue but if you look at the two sapphire rings at the top of the post, one of the sapphires is a darker blue than the other. Colour is quite difficult to describe as one person’s dark blue can differ from another person’s dark blue. Many gemmologists use a colour order system, the ‘World of Color’, based on a system developed by Professor Munsell at the beginning of the 20th century. This system uses three properties of colour to describe colour. These properties are hue (the basic colour of the stone), chroma (the intensity of the colour) and the value ( whether the colour is light or dark). Using this system, a sapphire’s colour can range from a dark greenish blue, a moderate blue, a dark blue, a deep blue, an intense blue, or a strong blue. All would be considered a true sapphire colour. The system allows different gemmologists and valuers to use the same descriptors when assessing a coloured gemstone.
Sapphires can be very expensive at any time but particularly if they have not undergone any treatments to improve colour and to remove inclusions. Sapphires have been admired for centuries and in great demand so it was not surprising that they were one of the earliest gemstones to be produced using synthetic processes at the beginning of the 20th century.