Natural rubies are found in several countries including Thailand and Mozambique, but it's in Myanmar that you'll find the finest and brightest of them all. Its fiery red hue, sometimes referred to as "pigeon's blood", is irresistible to connoisseurs and its value far exceeds those from other regions.

Thermal treated natural rubies are common, while natural rubies spared of thermal treatment—which still possess beautiful colour and clarity—are extremely rare. Even specialists can't identify all rubies by observation, which is why testing with a trusted gemological lab is often recommended.

Diamond

In its purest form, a diamond should appear colourless and its quality is determined based on the four Cs—colour, clarity, cut and carat weight. Colourless diamond grading starts from D (colourless) to Z (light yellow), and each colour grade represents a very subtle difference in hue.

One or two colour grade deviations can't be recognized by the untrained eye, particularly when mounted. Therefore, diamond jewellery such as necklaces are often composed of diamonds of three to five varying grades. To match diamonds of exact quality is no easy feat, and always incurs a premium in the price.

When it comes to coloured diamonds, the more obvious and pure the colour, the rarer the stone.

Yellow is one of the most common colours to appear in natural diamonds, and depending on saturation and tone, the rating for yellow diamonds ranges from "Fancy Light" to "Fancy Vivid Yellow".

Green is one of the rarest hues observed in natural fancy coloured diamonds, as it requires steady and intense natural radioactivity penetrating through the entire diamond rough over a significant period of time. A natural, pure intense green diamond of over 5 carats with good clarity is definitely a one-in-a-million specimen. 

The value of a coloured diamond is calculated by price per carat, and there is at least a 50% price difference between each colour grade. 

Emerald

Aside from green diamonds, Emeralds are one of the most sought-after green gemstones. And as far as provenance goes, emeralds sourced in Colombia are considered to be of the highest quality thanks to their rich, saturated blue-green colour. Clarity treatment to improve the visual beauty and stability of emeralds is very common and has been an established practice for centuries.  

This astonishing 19.90-carat emerald on offer at Phillips, completely spared of oil treatment and endowed with excellent clarity, is an extremely rare find in the market and a true gift from Mother Nature.

Jade

Jadeite jade has strong ties to Chinese culture and can appear in several colours including red, yellow, purple and black, although green jadeite is the most precious. When buying jadeite, the intensity and purity of the colour, plus translucency and texture, determine its value.

Traditionally, jadeite cabochons, beads and bangles are highly sought after as they often require large, high-quality roughs. Nowadays, jadeite jewellery has become more versatile for daily life.

Sapphire

Sapphire is a royal stone, and gem-quality sapphires hail from various countries including Myanmar, Sri Lanka and Madagascar. However, Burmese sapphire is set apart for its crisp transparency and robust brilliance, and is highly sought after for its "Royal Blue" variations. Modern mines in Burma yield very few sapphires, and fine examples over 10 carats like those on offer at "Jewels and Jadeite" are of utmost rarity.

There is no better way to learn how to spot top-quality stones than to see the actual works of art in person and speak with a specialist. Visit Phillips' "Jewels and Jadeite" public viewing at the Mandarin Oriental from November 23 to 26, where a stunning collection of rare and fine jewels will be on display.

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Phillips "Jewels and Jadeite"
Public Viewing: 23-26 November, 10am–6pm
Auction: 27 November 2017, 2:30pm
Venue: Mandarin Oriental, 5 Connaught Road, Central