The Verneuil Process: How the First Lab Made Rubies Changed Gemstones

The Verneuil process, also called flame fusion, is the method that first made synthetic gemstones on an industrial scale: very pure aluminum oxide powder is dropped through a hydrogen and oxygen flame, melts, and crystallizes drop by drop into a single crystal of ruby or sapphire. French chemist Auguste Verneuil announced it publicly in 1902, and it is still in use today. If you are shopping for colored gems in Beverly Hills, or anywhere, this is the reason a lab report matters as much as a beautiful color.

What is a ruby, chemically?

Ruby and sapphire are the same mineral: corundum, crystalline aluminum oxide (Al2O3). Pure corundum is colorless. A trace of chromium turns it red, and we call it ruby. Iron and titanium together turn it blue, and we call it sapphire. I explored the chemistry of these colors in Ruby, Sapphire and Emerald: The Science of Colored Gemstones.

That simple recipe is exactly what made rubies a target for chemists in the nineteenth century. If you could melt aluminum oxide with a little chromium and let it crystallize slowly enough, you would have a real ruby, identical in chemistry to one from the earth.

Who was Auguste Verneuil?

According to Wikipedia's history of the method, Verneuil was a Parisian chemist who in 1876 became assistant to Edmond Frémy, who was growing small rubies from molten alumina. Verneuil then developed flame fusion on his own. Wikipedia reports that he worked on it from the 1880s, documented it in sealed papers during the 1890s, announced it publicly in 1902 and published the full details in 1904. Britannica dates the process to 1902. Wikipedia also notes that so called Geneva rubies sold in 1885 were probably earlier flame fusion stones made by others.

How does the Verneuil process work?

The setup is surprisingly elegant. Both Wikipedia and Britannica describe the same basic steps:

• The powder. Finely ground, highly purified alumina sits in a container with a fine sieve at its base. A small hammer or vibration taps the container so powder sifts down at a steady rate.
• The flame. Oxygen carries the powder down a tube into a stream of hydrogen, and the two burn as an inverted torch. Wikipedia gives the core of the flame as at least 2,000 °C. Britannica gives the melting point of colorless sapphire as 2,030 °C.
• The drop. The powder melts into tiny droplets that fall onto a support. A seed crystal forms at the tip, and the molten top of the growing crystal keeps catching new droplets.
• The boule. The support is lowered slowly, so the crystal grows downward into a pear shaped single crystal called a boule. Wikipedia gives a typical commercial boule as about 13 mm wide and 25 to 50 mm long, around 125 carats. Britannica says boules normally reach 150 to 200 carats.

Add chromium oxide to the powder and you grow ruby. Britannica notes that iron and titanium give blue sapphire, and that spinel can also be grown in many colors this way.

How do gemologists tell a flame fusion ruby from a natural one?

Because the chemistry is the same, the clues are in how the crystal grew. Wikipedia describes two classic signs:

• Curved growth lines. Flame fusion crystals grow in a steep temperature gradient, leaving curved striae. Natural corundum shows straight, angular growth lines that follow its crystal structure.
• Round gas bubbles. Tiny bubbles are common in flame fusion stones. Natural stones usually hold solid crystals or fluid inclusions instead.

Wikipedia adds that strong magnification is usually required to see these features, which is why a gemological lab report is the reliable way to know what you have. The same principle applies to diamonds today, as I explained in How Gemologists Tell Natural From Lab Grown Diamonds.

Why did this invention matter so much?

Wikipedia calls the Verneuil method the first commercially successful way to manufacture synthetic gemstones and the founding step of modern industrial crystal growth. The numbers it reports show the scale: about 1,000 kg of synthetic corundum produced in 1907, and around 250,000 kg a year by 2000. Synthetic ruby later found uses far from jewelry, including the first laser, a story I told in The First Laser Was a Ruby.

It also changed how we think about value. Once a ruby could be grown in hours, rarity alone stopped being the whole story. Origin, documentation and craftsmanship became part of what you are really buying.

Natural, lab grown and honest labels

A lab grown gem is not a fake. It is the same material, made by people instead of by the earth. What matters is that it is described honestly. At Margaret Krinetz Fine Jewelry, handmade in Tel Aviv and shipped to Beverly Hills, I work with natural stones, and each product page states exactly what is set in it. The Diamond Studs, for example, hold 1.5 ct total of GIA certified natural diamonds in yellow gold, so the origin is documented, not assumed.

Emerald is a different mineral altogether, a beryl rather than a corundum, but the same questions apply. My Baby Allure Oval Emerald Studs are a small, everyday way to wear green.

Frequently asked questions

Is a Verneuil ruby a real ruby?
Chemically, yes. It is corundum colored by chromium, like a natural ruby. It is a synthetic ruby, and it should always be sold as one.

Is the Verneuil process still used?
Yes. Wikipedia describes it as still a leading method for synthetic corundum and spinel.

How long does delivery to Beverly Hills take?
Every piece is handmade to order in 4 to 6 weeks, then DHL Express delivers to Beverly Hills in 3 to 5 business days, with free shipping over $1,500.

Do you love the story behind a gem as much as the gem itself? Tell me which stone you are curious about through the contact page, and I will tell you what science says about it.