One of the most important criteria in judging a gemstone’s value is the perceived beauty of its colour. However, sometimes it’s difficult to put into words why one gem looks nicer than the next and often this is due to slight differences in the saturation of colour.
Colour itself is broken into three distinct components: hue, saturation and tone. As colour plays such an important role in evaluating gems, all of these are covered under separate headings in the book. But as a quick summary; hue is what most people would traditionally call colour: red, blue, purple, orange etc are all hues. Tone is also simple to understand and refers to the lightness or darkness of a colour. White has zero tone and black has 100% tone. For example Sky Blue Topaz has a tone of approximately 25%, whereas London Blue has a tone of around 85%. The more complex component of colour and most possibly the most important one for gem aficionados to fully comprehend is saturation.
Let us compare the dull saturation of yellow butter, with the vividly saturated yellow of a cycling Day-Glo vest. The hue is the same, but it is the vividness of the saturation that is very different. Saturation can be described as the vividness, the liveliness, the brightness or the loudness of a colour.
But what does all of this have to do with the heading of this piece - the Gamut Point? Well, the tone of a colour is partly responsible for the saturation of colour. Each different hue has a different level of tone that unlocks the most vivid saturation possible. This point is known as the optimum Gamut Point, or as I prefer to call it, the “Grand Prix”.
Technically speaking, at a tone of around 75% to 85%, a blue hue will exude the most saturation. At 85% tone in a blue hue, you hit what is known as the Gamut Point and once you go past 85%, a blue hue will dramatically fall of a cliff in terms of its saturation.
But aren’t lightly toned Ceylon Sapphires regarded by many as some of the best in the world and isn’t the famed dark toned Kashmir Sapphire incredibly sought after? The answer to both, of course, is yes. This is part of the magic of buying gemstones: you need to arrive at a balance of many things, including saturation of colour, clarity, the brilliance of the gem and of course the pedigree of the origin.
Remember, although there is general consensus in the gem industry about what constitutes the best colour or the best origin, it’s really a matter of choice and what I recommend is that you purchase gems based on what you like best. Put simply, the best colour a Blue Sapphire can be is the one that excites you the most. The one that floats your boat! You may prefer more pastel tones and love the extra brilliance that is seen in lighter gems, whilst others might prefer the dark, mesmerising midnight blues with their dark, rich colour. However, technically speaking, the most vividness of colour, the liveliest of colour tends to be those with a medium tone.
Let’s stay with blue for a second. The Grand Prix of tones is scientifically proven to be at around 80%. Therefore if we think about Tanzanite and the A, AA, AAA and AAAA system for grading tone, you will often find that an AAA grade will be livelier and more vivid than an AAAA. So if the tone in AAAA often passes the Gamut Point, then why is it so highly prized? Well, a good friend of mine, an ex-employee of Tanzanite One who are a large mining company in Tanzania, told me that early on they were struggling to sell the darker pieces: the medium tones (as you would expect with their vividness of colour) were more popular. So they invented the scale to try and help sell the darker pieces! Whether this is true or not, I am not sure. AAAA is without doubt a fabulous tone in terms of Tanzanite and often will wonderfully unlock flashes of secondary colours of violet and pink, but many of them certainly do pass the Gamut Point and lose their vividness of colour. For me the Grand Prix of Tanzanite is a tone that is at the higher end of AAA or one that just crosses the border into an AAAA.
Staying with blue gemstones, out of the three different tones of Blue Topaz, Sky, Swiss and London, the Grand Prix tone for me sits between the darker end of Swiss Blue to the lighter end of London Blue.
Purple hues behave very similarly in that the Gamut Point, the “Grand Prix” of its colour, is a tone of also around 80%. When Amethyst comes out of the ground with a tone over 85% it is often heat treated in order to reduce the tone and increase the saturation.
For yellow hues, the Grand Prix, the most vivid colour is a tone of approximately 15%. Any lighter than this and you will get a beautiful gem that exudes brilliance, but you won’t see the optimal vividness of saturation. If the tone is much darker than this, then the colour will still be very appealing (in fact many might prefer it) but the optimum saturation point, the Gamut Point, the Grand Prix of the gem will have been passed.
For a green Emerald, a gem sitting on the pole position on the grid, one with the best opportunity to win the Grand Prix is one with a tone in the range of 40%. Whilst some will prefer the openness of the colour of pastel greens and others being fond of the darker tones of forest greens, all other things being equal in terms of quality of cut, carat weight and clarity, a gem expert will normally value more highly one with a vivid, lively colour.
