Saturation and transparency typically influence the beauty of a gemstone more than tone.Įven though there are several industry colour grading systems (e.g. Saturation is described as the intensity (strength or purity) of a colour.Tone is the degree of lightness or darkness of a colour.It is described as the shade, tint or sensation of colour. Hue is the position of a colour on a colour wheel.As always, be guided by common sense and your preferences, paying heed to the inherent characteristics of each type.
Scrutinising a gemstone under a variety of different light sources before purchasing is definitely a good idea. While some gemstones look better in natural daylight and others in artificial (incandescent) light, a gemstone's colours should ideally remain beautiful in any light source. In extreme examples, this results in the colour change effect. Even a small variation in the light source can produce a big difference in how we see a gem's colour. It is changes in a light source's component colours that cause gems to look different in dissimilar lighting conditions. If all spectral colours pass through a gem it appears colourless, but if these are all absorbed it will appear black.Ī red gemstone appears red because all the other colours of the spectrum except red are absorbed by the gem. This absorption of certain colours is called the 'selective absorption of light' and is always the same for an individual gemstone. The spectral colours of white light least absorbed combine to produce the colour of the gem. When white light passes through a gem, some of these spectral colours are absorbed. But for most gems, and even most objects, our perception of colour involves an amazing transformation.Īs revealed by rainbows, white light is comprised of the individual colours of the spectrum: blue, green, orange, red, violet and yellow. Some gems, such as Opal, get their colours physically as light is refracted in flashes of colours that change with the angle of observation ('play of colour'). Most things get their colour due to how they react with light. Without colouring elements (and/or colour centres), all Sapphires would be colourless.
In their pure state, 'other coloured' minerals are colourless, for example Sapphire. For example, Peridot will always be shades of green from its high iron content, which comprises 12-15 percent of its total mass.Ģ.Other Coloured (Allochromatic): Colour is caused by small amounts of colouring elements that are not part of the mineral's normal crystal structure and/or crystal imperfections (colour centres). In general, intense colours are more favoured than those that are dark or light, but there are exceptions, for example, that Victorian favourite, Rose de France Amethyst.īut how does colour actually work? Simplistically, gemstone colour occurs in two ways:ġ.Self Coloured (Idiochromatic): A colouring element is incorporated into the mineral's crystal structure, always giving it a characteristic colour. Inversely, if a gem's colour is popular and it's rare, such as Paraíba Tourmaline or Padparadscha Sapphire, then you've got a gemstone superstar. Fashion is easy to understand, it's all about colour popularity if no one finds a gem's colour attractive, then its rarity really doesn't matter. The most valuable colours depend on two factors, fashion and rarity. It will come as no surprise that the more attractive a gem's colour, the higher the value.
This is not to say that there are no colour paradigms in gemstones, there certainly are, but these should never be at the expense of personal preferences. But like everything to do with beauty, it is highly subjective and at the end of the day, in the eye of the beholder. Yellow Sapphire is an 'other coloured' gemstoneĬolour is the single most important factor when assessing coloured gemstones.
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