Yellow diamonds are much rarer than the classic clear diamonds, but they are more often seen than the other fancy diamond colours. Yellow diamonds are sometimes called canary diamonds after the bird's brilliant yellow plumage.

Yellow diamonds were scarce until the large diamond mines of South Africa were opened up in the 1860s. Although yellow coloured diamonds are less commonly found than colourless or white diamonds, they are the most frequently seen of the fancy coloured diamonds. Diamond experts suggest that yellow diamonds account for around 60% of all coloured diamonds. The number of yellow diamonds, in comparison to all diamonds, is tiny at about 1 in 5000 making them, in real terms, very rare.

Unlike all other diamond colours, the yellow diamond is related to the classic clear diamond. Most clear diamonds have a very faint hint of yellow colouration. Yellow diamonds can be thought of as being heavily coloured clear diamonds. The lightest yellow gems are part of the colouration scale for clear diamonds.

What Is A Canary Yellow Diamond?

All but the very clearest of clear diamonds have a slight trace of nitrogen bonded into the crystalline lattice of carbon that is diamond. The nitrogen causes the gem to absorb blue light leading to the diamonds looking yellow in colour. The more nitrogen is present in the crystal's structure, the more yellow the diamond will appear.

Yellow diamonds are found wherever clear diamonds are found among the most significant sources are Australia, Central Africa and Borneo.

The most valuable (and beautiful) yellow diamonds are generally those with the purest, deepest, colouration. Secondary colours from other trace impurities or physical changes to the diamond give a vast range of possible colours and intensities. Some secondary colours can increase the value of the diamond even higher than a pure colour. For example, green or orange secondary hues can increase the value while brown will decrease the value.

Natural And Treated Yellow Diamonds

Because yellow diamonds are both rare and expensive, technology has been used to supply the market with lower-cost alternatives. Some of these alternatives are very high quality and difficult to tell apart from natural yellow diamonds.

1. High pressure and high-temperature techniques HPHT that mimic natural processes deep beneath the Earth's crust can be used to turn relatively inexpensive brown diamonds into more desirable yellow ones. HPHT treated diamonds have a permanent colour.
2. Bombarding diamonds with radiation, in a process called irradiation, can produce entirely safe yellow, and other colour diamonds.
3. Annealing, another high-temperature process can be used to add colour to diamonds that are already somewhat yellow.Both irradiation and annealing produce diamonds that will change colour under the extreme heat used in repairing jewellery settings and so the process is not regarded as being permanent. If you have such diamonds, it is essential to inform the jeweller before any repairs are carried out.

4. The final category of treatment is diamond coating. A thin layer is added to the diamond to give the desired colour. This process is not permanent as heat and chemicals, or even scratching can damage the coating. Before any repairs or polishing are carried out, the jeweller needs to be informed so that precautions can be taken.

There is no particular problem with having treated yellow diamonds in your jewellery as long as you know about it. Treated diamonds enable people to buy beautiful yellow diamonds at a significantly lower cost than for natural gemstones.Jewellers should always tell you if a diamond has been treated, but sometimes that does not happen. A reputable diamond grading report will protect you by informing you of the diamond you are thinking of buying is not natural.

How Are Yellow Diamonds Graded?

Diamonds are graded according to the industry standard 4Cs devised by the Gemological Institute of America (GIA). The GIA is the leading diamond grading organisation in the world. The 4Cs are Cut, Clarity, Colour, Carat Weight. Clear diamond assessments emphasise clarity, those for coloured diamond emphasise the colour. Many buyers are willing to compromise the clarity grade in order to have the best possible colour.

Yellow Diamond Colour Grades

A yellow diamond that has no secondary colours is regarded as being pure. Where secondary colours are present, they are likely to be brown, green, or orange. The GIA colour grading scheme has a fixed naming convention for all coloured diamonds. If the secondary colour is less intense then the primary colour the name will appear in the following form: greenish-yellow. If the colour is pure, it is recorded as yellow. Where the yellow colour is less strong than the other colour the stone is no longer a yellow diamond and the colour is shown as yellowish-green.

Yellow Diamond Colour Intensity

Buyers of yellow coloured diamonds are interested in more than just the colour of the stone. The intensity of the colour is just as important, given that darker coloured diamonds are generally preferred over lighter ones. The GIA uses a consistent scale for this aspect of the diamond's appearance as well. Coloured diamonds are graded on a nine-point scale ranging from Faint to Fancy Vivid. Yellow diamonds use only 6 of these grades because the lightest three grades of yellow diamond appear on the clear diamond colour scale. The scale for yellow diamonds is as follows: Fancy Light, Fancy, Fancy Intense, Fancy Dark, Fancy Deep and Fancy Vivid. Most yellow diamonds used for jewellery are from these grades: Fancy Light, Fancy, Fancy Intense and Fancy Vivid.

Figure 1. Courtesy: https://4cs.gia.edu/en-us/blog/how-to-choose-yellow-diamond-engagement-ring/#yellow-diamond-engagement-ring

Figure 2. This chart shows the subtle transitions in GIA’s colour grading of yellow diamonds. Note, too, that the fancy grades represent a range of colour sensations, not a “single” colour sensation. Photo: Elizabeth Schrader and C. D. Mengason/GIA

Making the grading of yellow diamonds a little harder is the fact that diamonds can be cut to enhance the colour. A recut diamond can even be regraded to reflect the new appearance. This means that two diamonds with the same colour grade, but a different cut shape can look somewhat different in terms of their colour.

Cut, Clarity, And Carat Gradings

A full coloured diamond grading report from the GIA will tell the prospective buyer about the colour and even if the diamond's colour is natural or the result of a laboratory treatment.

The other 3Cs are the same as for clear diamonds. When buying a yellow diamond rather than concentrating upon the clarity, buyers will accept diamonds with more flaws than would be preferred in a clear stone. The cut is important as good cutting can make a diamond look more yellow than its grade might suggest and so can be worth paying for. Larger coloured diamonds are relatively rare, so carat prices are usually higher per carat than for clear stones. Larger yellow diamonds will tend always to look darker because light has further to travel through the gemstone.

Grading Reports Are Vital!

Determining the differences between yellow coloured diamonds is a skilled process. When you buy a yellow diamond, you need to know that you are getting what you wanted. A GIA, or similar, report gives that assurance. Not all yellow diamonds are naturally coloured. There are techniques to change or improve the colour you see. GIA colour reports tell the buyer whether a diamond is naturally or artificially coloured.