Gas Bubbles in Synthetic Ruby

Don’t Be Caught Out by a Synthetic Ruby

At E.D.R – European Diamond & Gemstone Reports, we recently examined a striking 5 ct antique ruby ring submitted by a customer eager to determine the authenticity and value of their purchase. What looked like a remarkable bargain turned out to be a synthetic ruby – and the clue was a cluster of tiny gas bubbles.

What We Found Under the Microscope

Initial expectations shifted upon close inspection under our microscope, where we observed distinct round gas bubble inclusions within the gemstone. Natural rubies, by contrast, typically display inclusions such as fine rutile needles (“silk”), angular mineral crystals, fingerprints and straight or angular colour zoning that follows the crystal’s growth.

The presence of gas bubble inclusions is significant; these tiny spherical voids indicate that the stone was created in a controlled environment, distinguishing it from a natural ruby. In this case the bubbles were accompanied by faint curved growth lines, a second hallmark of flame-fusion material.

A Brief History of the Synthetic Ruby

These inclusions are characteristic of synthetic rubies, first introduced to the market in the late 19th century, specifically with the advent of the Verneuil flame-fusion process, commercialised in 1902. Auguste Verneuil’s method drips powdered aluminium oxide and chromium through an oxy-hydrogen flame, building up a carrot-shaped crystal called a boule in a matter of hours.

This method allowed for the creation of rubies that closely mimic the colour and clarity of natural stones, yet their internal characteristics often reveal their true origin. Later techniques, including flux growth (from the 1950s) and hydrothermal growth, produce more convincing material with different tell-tale inclusions, such as wispy flux “fingerprints” and platinum platelets from the crucible.

How to Tell a Synthetic Ruby from a Natural One

• Gas bubbles: perfectly round, sometimes elongated or in strings, and often concentrated in one area – rare in natural corundum.
• Curved striae: curved growth lines or colour banding, visible under magnification with diffused lighting, that follow the shape of the boule. Natural stones show straight, angular zoning.
• Absence of natural inclusions: a large, bright red stone that is completely clean at 10x should always raise suspicion.
• Strong fluorescence: many flame-fusion stones glow very strongly red under UV light because they contain no iron to dampen the reaction.
• Antique settings are no guarantee: Verneuil material has been set into jewellery for well over a century, so a genuinely old ring can hold a synthetic stone.

Separating these from treated natural stones is just as important. Our articles on lead glass filling and heat treatment in corundum explain the other features we look for, and the Gemological Institute of America (GIA) publishes detailed reference images of each type of inclusion.

What It Means for Value

While the visual appeal of the antique ring remains undeniable, the identification of these bubble inclusions means the gemstone is synthetic, which has considerable implications for its market value. Given that synthetic rubies are generally far more accessible in terms of price than their natural counterparts – often a few pounds per carat rather than thousands – this discovery led our client to reassess the true worth of their antique ring.

It is worth remembering that a synthetic ruby is a real ruby in terms of chemistry and hardness; it simply lacks rarity. The problem arises only when it is sold, knowingly or not, as a natural stone. Our findings emphasise the importance of thorough verification in the gemstone market, ensuring buyers are fully informed about the origins and characteristics of their purchases, especially when it comes to antique pieces that may have a fascinating history.

Get Your Rubies Tested

If you have any questions, or would like to get your rubies tested or valued by our expert gemstone valuation team, then feel free to get in touch! Every stone we examine receives a Loose Gemstones Report or Jewellery Card Report stating clearly whether it is natural or synthetic. You can also read more about the July birthstone and what makes a fine natural ruby so valuable.