Are Coloured Stones Graded?

Are Coloured Stones Graded?

We have a fantastic collection of coloured stones; sapphires, rubies, emeralds, aquamarines and tanzanites and they are often popular choices for engagement rings or anniversary jewellery. But it has become clear that many of our customers are uncertain as to how coloured stones are certified. It is often assumed that they are graded in the same way as diamonds, but this is a common misconception as they are not. They can indeed be certified, but the criteria is somewhat different. Read on to explore how! For certification of a coloured stone, a laboratory such as the GIA will provide the following information:
  • Dimensions
  • Carat weight
  • Cut
  • Shape
  • Description of colour
  • Geographical origin
  • The presence of any treatments


Note: there is no clarity grade. Unlike diamonds in which the ‘4 C’s’ are the key characteristics under scrutiny, with coloured gemstones there are two main reasons why you may want a certificate: to confirm the geographical origin of the stone and whether or not there is evidence of any treatments. If the gemstone is not from a particularly sought after location, and has received treatment, it will most likely not be certified - these are the vast majority of stones, and there just is little point to it. Rather than specifying which coloured stones are treated, it’s usually the other way around - you can safely assume that it has been treated unless specified otherwise.


Geographical Origin

There are certain geographical locations where stones are particularly sought after as they are deemed to be of a higher quality and more desirable colour. For example, Burmese rubies, Colombian emeralds and Kashmir or Ceylon sapphires, most of which probably sound familiar to you. A certificate will commonly state the geographical origin of the stone, as they assess the chemical structure of the gem and identify specific geological characteristics which they are able to attribute to it having come from a specific place. These locations command a premium, so it is worth having it on paper.

Presence of treatments

The second key reason you may want a coloured stone to be certified is to confirm that it has not received any treatments. The vast majority of sapphires, emeralds and rubies that you will see on the market will have been treated in some way, and these are deemed acceptable and do not reduce a gemstone’s value. For rubies and sapphires, it is predominantly a heat treatment used to even out colour or enhance clarity. For emeralds, it is common to receive an oil treatment to enhance clarity. However, if your chosen stone is naturally a very high quality and has not needed any of these very common treatments, they are relatively rare and unique and therefore will be much more expensive. Certification will identify the presence, and extent of, treatments and you will definitely want confirmation from a laboratory certificate to justify the higher price of an untreated stone.

What about the AAA system?

You may have heard of coloured gemstones being classed as AAA, AA, or A grade. This is a system used by some dealers and wholesalers in an attempt to create a standardised system to classify coloured stones into clearer, more distinct categories, in a similar way to diamond grading. This is predominantly to increase the commerciality of the gemstones as it is then easier to sell a stone that fits into a nice, neat category. However, it is not a wholly accepted system. It takes into consideration beauty and intensity of colour, transparency of the stone, quality of the cut, but the requirements are vague and not as clear as the diamond grading system. Consequently, you won’t see an A grade on a GIA certificate (or most certificates, for that matter).


How do you know that a coloured stone is a good colour and quality?

When you are choosing a sapphire, ruby, emerald or other coloured stone, there are some colours that are deemed to be more desirable, but please do bear in mind that this is highly subjective and largely down to individual taste. You may just prefer a lighter blue sapphire, or perhaps a very dark ruby - and that’s ok! The colours deemed to be ‘most desirable’ are based on the court of public opinion and are generally what most consider to be ‘most aesthetically appealing’ when considering a gemstone. At the end of the day, it is down to your own personal taste (and probably your own budget restrictions to some extent, too!). However, here are some key points to look out for when choosing a coloured stone:


  1. Intensity of colour: this is the saturation. Ideally, you would like a nice rich red, blue, green etc.
  2. Consistency of colour throughout the stone rather than patches or areas of lighter/darker colour.

  3. The lightness or darkness of the stone. If it is too dark or too light, the colour will be difficult to distinguish.

  4. Transparency: the stone should be transparent enough to enjoy a play of light throughout but not so transparent that it is insipid and weak. Generally, the more opaque a stone the duller the appearance.

  5. Lower clarity is generally more acceptable in coloured stones than in diamonds. The presence of inclusions in emeralds is widely accepted as part of the package, and it is increasingly unusual to find high quality, large rubies and sapphires that are completely clean. These stones will most likely have received some minor treatment to address these clarity issues, greatly reducing their visibility.


Hopefully, you have found this to be a helpful introduction to coloured stone certification and can now go forth in your jewellery search armed with the facts. But, if you have any further questions, please do not hesitate to get in touch. We are always more than happy to discuss the ins and outs of jewellery with you!

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