Precious Gemstones: A Collector's Guide to Sapphires, Rubies and Emeralds

The Big Three: Nature's Most Extraordinary Colours

While diamonds may dominate the engagement ring market, the world's most passionate gem collectors have always been drawn to colour. Sapphires, rubies and emeralds — known in the trade as the "Big Three" — have been treasured by royalty, worn by the powerful and coveted by connoisseurs for thousands of years.

At Sterling Diamond in Burlington Arcade, Mayfair, we source exceptional coloured gemstones from the world's most prestigious origins. This guide shares our expertise on what makes these stones so special, how they are graded, and what to look for when building a collection.

Stunning array of coloured precious gemstones

Sapphires: The Stone of Royalty

What Makes a Great Sapphire?

Sapphires are a variety of the mineral corundum (aluminium oxide), with trace amounts of iron and titanium creating their characteristic blue colour. But sapphires actually come in every colour except red (red corundum is classified as ruby).

The four factors of sapphire quality:

1. Colour — the most important factor. The ideal blue sapphire exhibits a vivid, saturated "cornflower blue" — neither too dark nor too light, with no grey or green undertones.
2. Clarity — sapphires typically contain some inclusions. "Eye-clean" stones (no inclusions visible to the naked eye) are considered excellent.
3. Cut — a well-cut sapphire maximises colour saturation and brilliance. Unlike diamonds, there is no standardised cut grading for sapphires.
4. Carat weight — fine sapphires over 5 carats are rare and command significant premiums.

Origin Matters

Unlike diamonds, where origin has little impact on value, a sapphire's geographic origin can dramatically affect its price:

Fancy Colour Sapphires

Beyond blue, sapphires occur in remarkable colours:

• Padparadscha — a rare pink-orange variety from Sri Lanka, among the most valuable gemstones per carat
• Pink sapphire — increasingly popular for engagement rings
• Yellow sapphire — bright and cheerful, excellent value
• Colour-change sapphire — shifts from blue in daylight to purple under incandescent light

Rubies: The King of Gemstones

What Makes a Great Ruby?

Rubies are also corundum, coloured red by trace amounts of chromium. The finest rubies are among the most valuable gemstones on earth — carat for carat, a top-quality ruby can exceed the price of a diamond.

The ideal ruby colour is described as "pigeon blood red" — a vivid, saturated red with a slight blue undertone and strong fluorescence that makes the stone appear to glow from within.

Origin and Value

Ruby Rarity

Fine rubies are rarer than diamonds of equivalent quality. A clean, unheated Burmese ruby over 3 carats is one of the rarest gemstones in existence. At auction, such stones regularly exceed £100,000 per carat.

Emeralds: The Green Fire

What Makes a Great Emerald?

Emeralds are a variety of the mineral beryl, coloured green by trace amounts of chromium and sometimes vanadium. Unlike sapphires and rubies, emeralds almost always contain visible inclusions — known in the trade as the "jardin" (French for "garden") because they resemble foliage.

The ideal emerald exhibits a vivid, saturated green with a slight blue undertone, good transparency despite inclusions, and a lively brilliance.

Origin and Value

Emerald Inclusions: A Feature, Not a Flaw

An "eye-clean" emerald is exceptionally rare and commands enormous premiums. Most emeralds are valued for their colour first and clarity second. A richly coloured emerald with visible inclusions is worth more than a pale, clean stone.

Precious gemstone set in an elegant ring

Treatments and Enhancements

Heat Treatment

Sapphires and rubies are routinely heat-treated to improve colour and clarity. This is an accepted, permanent treatment that does not significantly affect value — provided it is disclosed. Unheated stones of fine quality command premiums of 20–100%+ over heated equivalents.

Oil and Resin Treatment

Emeralds are almost universally treated with oil or resin to fill surface-reaching fractures and improve clarity. The industry classifies treatment levels as:

• None — untreated (extremely rare and valuable)
• Minor — slight enhancement (commands a premium)
• Moderate — standard treatment (the norm for fine emeralds)
• Significant — heavy treatment (lower value)

Beryllium Diffusion

Some sapphires are treated with beryllium diffusion — a process that alters colour throughout the stone. This is a more controversial treatment and should always be disclosed. Beryllium-diffused sapphires are worth significantly less than naturally coloured or simply heated stones.

Our Policy

At Sterling Diamond, every coloured gemstone is sold with full disclosure of any treatments. We provide independent laboratory reports from Gübelin, SSEF or GIA for significant stones, detailing origin, treatment status and quality assessment.

Investment Potential

Why Coloured Gemstones Are Appreciating

• Finite supply — unlike diamonds, there are no large-scale mining operations for fine coloured gems
• Growing demand — Asian and Middle Eastern markets are driving prices higher
• Rarity — top-quality stones are genuinely scarce, particularly from historic origins
• Portability — extraordinary value in a tiny, portable form

Recent Auction Records

• The Sunrise Ruby (25.59ct Burmese ruby) — $30.42 million (Sotheby's, 2015)
• The Blue Belle of Asia (392.52ct Ceylon sapphire) — $17.56 million (Christie's, 2014)
• The Rockefeller Emerald (18.04ct Colombian emerald) — $5.51 million (Christie's, 2017)

Best Investment Approach

1. Buy the best quality you can afford — top-tier stones appreciate fastest
2. Prioritise origin — Kashmir sapphires, Burmese rubies and Colombian emeralds hold value best
3. Insist on laboratory certification — provenance documentation is essential for resale
4. Choose unheated/untreated where possible — these command the highest premiums
5. Think long-term — coloured gemstones are a generational investment

Caring for Coloured Gemstones

Explore Our Gemstone Collection

Sterling Diamond sources exceptional sapphires, rubies and emeralds from the world's finest origins. Visit our Burlington Arcade showroom in Mayfair to view our current collection and discuss your requirements with our gemstone specialists.

Whether you are seeking a centre stone for a bespoke ring, adding to a collection, or exploring coloured gemstones for the first time, we are here to guide you.

Sterling Diamond — Burlington Arcade, Mayfair, London W1J 0QJ