Authenticity

Ruby is a variety of corundum, and sapphire is its family member, sharing the same chemical composition of aluminium oxide, crystallising in the trigonal system. It has an RI of 1.76 to 1.77 and a specific gravity of around 4.00. Pure corundum is colorless (white sapphire), while the red color in ruby is due to small amounts of chromic oxide.

Burmese rubies, colored by chromium, have a distinctive blood red hue, often called pigeon blood, and can exhibit strong fluorescence under artificial light, making them appear almost illuminated. Always view rubies in daylight, as their color can drastically change; a deep red stone might look like a washed-out pink outdoors.

Rubies from Sri Lanka tend to be more pink than true blood red, yet they are still attractive; their fluorescence is similar to Burmese stones, giving them a remarkable transformation at night.

Perhaps the most common source of rubies for jewelry today is Thailand. These stones can appear deceptive in daylight; Thai rubies have a brownish tinge due to iron and can resemble the blood red of Burmese stones. Iron inhibits fluorescence, causing Thai rubies to lack the ‘fire’ seen in Burmese or high-quality Sri Lankan rubies. While the difference is subtle, the value disparity is vast: a 5-carat gem-quality Burmese ruby can be worth ten to twenty times that of a similar quality Thai ruby.

Identifying Burmese stones among rubies requires knowledge of inclusions and flaws. Burmese rubies often feature calcite crystals that, alongside other traits, can indicate the stone’s origin from calcite schist.

evaluation

Among coloured gemstones, ruby is the most valuable, surpassed only by the rarest pink, blue, and green diamonds, and is prized mainly from one small region.

The town of Mogok in Upper Burma is remote and has been for hundreds of years; recently, the government restricted visas to foreigners to allow only the shortest stays.

For centuries, the finest rubies have come from this small area, but it wasn’t until the British annexed the region in the late nineteenth century that effective mining began under jeweler Edwin Streeter. However, the number of gem-quality stones over 5 carats found during British ownership was relatively small, and mining has virtually ceased since their departure before the Second World War.

Yet not all rubies from Burma are valuable. Ruby is not a rare gemstone; some Burmese stones might be worth as little as $20 per carat, while others can reach $200,000 per carat.

The value balances the richness and beauty of the color, purity, and flaws. A cynic might say that rarity matters too. However, given the choice between a fine ruby from Burma and one from Thailand, most would choose the former for its beauty. Yet, the amateur seldom has a stone for comparison.

Other ruby sources include East Africa (Kenya and Tanzania) and Pakistan, which are relatively new but effective.

Alternative Gemstones Mistaken for Rubies

Natural red spinel is an attractive and effective gemstone and can be easily differentiated from ruby using a refractometer (spinel has an RI of 1.72).

Where the use of this instrument is impossible due to a protruding setting, the cubic crystalline structure of the stone, being singly refractive, will validate its use; unlike ruby, it will show no dichroism through a dichroscope and remains unchanged under a polariscope. The color of red spinel is generally more strawberry than the characteristic raspberry of ruby, often described as ‘sweet’ or ‘sugary’. Like many Burmese and Sri Lankan rubies, spinels are highly fluorescent. The ‘silk’ phenomenon, common to these rubies, appears as a whitish sheen within the stone due to minute filaments of rutile. Characteristic inclusions in red spinel are crystals resembling bubbles, which may lead amateurs to mistake it for red paste.

Red tourmaline, often confused with ruby, is known as ‘rubellite’ but rarely matches ruby’s true red. It can be differentiated by its refractive index (1.62-1.64) and double refraction of .018. Unlike ruby, it is never fluorescent. Confusion may arise in low-quality stones with minimal price differences, but familiarity with tourmaline’s pinkish-red hue makes this unlikely. Characteristic whitish inclusions and typical coloration resemble raspberry-flavored sweets.

Garnets are often confused with ruby, and their RI overlaps with ruby, making refractometer use risky. Luckily, they are singly refractive and show no dichroism through the dichroscope; however, this instrument is awkward to use and is mainly useful for unmounted stones. Perhaps more useful is the fact they remain unchanged under the polariscope. Rare pyrope garnets can match the blood red of fine rubies but have a lower RI of 1.74 to 1.75. Almandine garnets are colored by iron, unlike pyropes which are colored by chromium, and are non-fluorescent. They may be confused with Thai rubies, but a pocket spectroscope can help clear this up. The three broad absorption bands of almandine are visible even to amateurs (see also section on garnets). Red pastes can be identified with a pocket lens; watch for gas bubbles (n.b. red spinel) and color swirls.

Other Practices

Synthetic ruby, like all synthetic materials, has the same crystal structure and chemical composition as its natural counterpart, making traditional testing tools like the refractometer ineffective. Synthetic rubies and sapphires have existed since the early 1900s, when French scientist Verneuil developed a furnace to crystallize pure alumina and metallic coloring agents through an oxy-hydrogen flame into ‘boules.’ This rapid process results in noticeable curved bands and trapped gas bubbles within the stones, making detection easier. When synthetic rubies became available, jewellers quickly adopted them. In a notable case, Sotheby’s sold a historical revival necklace by Giacinto Mellilo, with its small rubies later identified as synthetic, raising the question of whether Mellilo recognized the difference before World War I.

Fortunately, even small rubies often have flaws; over 1 carat, it’s rare to find such stones without imperfections, while large synthetic rubies are common due to their low production costs, often raising suspicion with their ‘too good to be true’ color. Any ruby over 1 carat that is virtually flawless should be tested, as synthetic rubies, colored by chromium, exhibit spectacular fluorescence under artificial and ultraviolet light. Careful examination with a pocket lens or microscope will reveal curved color bands and small gas bubbles for a conclusive diagnosis. Awareness of synthetic rubies may deter amateurs from being misled by large stones.

Where smaller stones less than a third of a carat are used in jewelry, the problem is greater. Using synthetic rubies and sapphires in designs like brooches and bracelets from 1920-1950 is common. Although natural stones of this size are relatively inexpensive, the real cost is often in cutting, and a jewel with synthetics can be hard to resell due to buyer reluctance. In small synthetic stones, flaws may be hard to detect, while natural rubies rarely match in hue, making selection impractical. With synthetics, this issue rarely occurs. If all stones under a lens share the same colour and appear flawless, buyers should be cautious. Ultimately, the jewel’s quality—examining the colour and purity of diamonds and other stones, setting, and craftsmanship—will indicate its true value.

The march of science has introduced new methods for producing synthetic stones, like the ‘Kashan’ rubies, which pose challenges for gemmologists.