As discussed elsewhere in this book, colours are made up of three elements: hue, saturation and tone. ‘Saturation’, also referred to as colour purity, describes the pureness of the hue: its vividness and intensity. If a gemstone was pure grey or pure brown, it would be described as having zero colour saturation. When greys or browns are seen in a coloured gemstone, they tend to dilute the beauty of the colour. At the other end of the scale, if the colour has very little grey or brown in it, it is described as a vivid colour (it is worth noting that no colour produced by Mother Nature has 100% saturation). The GIA describes six levels of saturation; Greyish Brown, slightly Greyish Brown, very slightly Greyish Brown, moderately strong colour, strong colour and vivid colour.
As a general rule of thumb, the higher the saturation in a gemstone, the more valuable it becomes. Sometimes the saturation is even more important than the hue itself. For example a violetish Blue Sapphire with a vivid saturation, would most likely cost more than a pure Blue Sapphire which had a greyish brown saturation.
