How to judge a blue sapphire's quality

Let’s dive into how gemologists and gem dealers judge a blue sapphire by its colour, so you’ll have some guide-lines in case you’d like to invest in a blue sapphire for yourself, a loved one!

Why colour matters

Firstly, why do I hammer so much on colour here?

Because colour is the most important asset a colour stone possesses!

In other words, a coloured gemstone’s value is first and foremost determined by its colour.

The better its colour, the higher its value in the market. 

Even if the stone doesn’t have a perfect cut or clarity…

Those features are of secondary importance. Even in the top segment: we always look at colour, colour...

And colour.

You get the idea.

By the way, this is contrary to diamonds whose most important characteristic is its brilliant sparkle. And not its colour (for the vast majority of diamond purchases out there). 

Most diamonds are colourless and so they need to get their fame from something else than colour - which also happens to be the reason why probably most women want one: their out-of-this-world flashing sparkling brilliance. 

And that sparkle mainly comes as a result of good, highly precise and symmetrical cutting. 

So with diamonds, judging the symmetry of their cut is more important. Far more than judging their colour.

Back to the blue sapphire and how to colour grade it.

Colour grading blue sapphires 101

To colour grade a blue sapphire - and any other coloured gemstone for that matter, we look at these 3 features: 

  • Its hue,
  • Its saturation and
  • Its tone

Blue hues

To start with the hue.

You need to determine what is the stone’s primary and secondary colour, if it has one.

This may seem easy but it’s more tricky than you think.

(Ideally, you have to see hundreds or - like gem dealers - thousands of stones a year to train your eye...).

Blue sapphire - like ruby - is a primary colour gemstone. And so, the purer the primary hue, the better. 

So, the best blue sapphire is blue! 

Louis Vuitton Blue Sapphire Earrings
Some top colour blue sapphires in Louis Vuitton's high jewellery line…


That sounds obvious, but isn’t always the case in practice. 

As it’s almost impossible to find pure hues in nature. 

Most coloured stones have some mix of colours. And that's why experts always try to determine a stone's primary and secondary colour.

In practice the best quality blue sapphire has:

Blue as its primary colour for about 85-90%.

And has a secondary purplish hue of no more than 10-15%.

Sizzling saturation

Then, the saturation.

This refers to the intensity of the hue.

The brighter the colour is, the better. 

There shouldn’t be any grey and brown hints masking over the colour.

If there are, they decrease the colour’s intensity. 

For blue sapphire, it’s grey which  is called the normal “saturation modifier”.

And already a slight grey mask will give a cold or slightly “steely” quality to the normally warm hue of a blue sapphire. 

You may be surprised to hear that I use the word “warm” when it comes to the colour blue! 

We tend to call that a cold colour, right? 

However, in fact all pure chromatic hues are vivid and bright and not “cold” at all, not even blue. 

The best and purest blue is not cold but rather velvety and warm. 

The fact that you (or me too before I went to Bangkok’s gem hub) think that blue tends to be cold, just means you have probably never seen a fine quality blue sapphire in your life (yet!)…

This makes total sense as most blue sapphires you come across in the West tend to be either very dark (going towards black) or are greyish, and yeah, those stones are cold and not very attractive. 

I also notice that when I mention the stone 'blue sapphire' some people tell me they feel these stones are a bit dusty, conservative and old-fashioned (the same thing for rubies). 

However, the fine quality stones I refer to here are of an intense vivid blue. 

And besides being velvety warm, they are also incredibly fashion-forward and by no means conservative, wouldn't you agree?! 

Chaumet Blue Sapphire Ring

Still think blue sapphire is old-fashioned? An exquisite ring by Chaumet. 

Simply because the best colours are outspoken. And there's nothing conservative about that.

So to sum up, if the key colour of a blue sapphire actually does appear as cold and dull, it’s an indication that the stone has a grey mask.

And you may keep on walking.

Toning up or down?

Lastly, the tone. 

This refers to the appearance of blackness in a stone.

A quality sapphire should be quite dark-toned: for about 70-80%. 

Now let’s complicate matters a bit more!

In addition to the above three features that you should always look at, some connoisseurs have other preferences...

Colour wheel: How to Judge Blue Sapphire's Quality


For example, some prefer a distinct purplish secondary hue because they feel it adds a “velvety richness” to the blue. 

And when you have a look at the colour wheel image above, you can see how purple indeed adds even more soft richness to the colour. 

Others prefer a purer, more “open” blue with a slightly lighter tone (75%). 

Whatever the case may be, any green hue should be avoided in the blue! 

If it does contain a bit of green, the price and the stone’s value come crashing down into the commercial range. 

Good luck with your hunt for the perfect blue sapphire!

And if you’d like some guidance with sourcing the right blue sapphire for you and turning it into a bespoke piece, contact me here.

I’d love to see how I can help.


I hope the above helps you on your gemstone piece journey and if you need any help in sourcing a special coloured gemstone (like a fine blue sapphire) or with creating your own bespoke gemstone jewellery piece, feel free to contact me here at

For more gem stories and insider tips on how to buy your own investment-worthy gemstones, follow me on Instagram @evagemsandjewels. 


Until next time,
Eva xxx