Summary
People have highly prized sapphires for ages. Their beauty and hardness make them ideal choices for jewelry. The demand for sapphires, however, has long exceeded the natural supply. In fact, gem-quality corundum, which includes sapphires and rubies, is rarer than diamond. Not surprisingly, sapphires and rubies were some of the first gemstones to be synthesized over 100 years ago. Manufacturers still use some of the technological methods used then to synthesize sapphires today.

So, can you tell the difference between natural sapphires and lab-grown sapphires?

Reading time: 4 min
790-ct synthetic sapphire - lab-grown sapphires

This 790-ct sapphire was cut from colorless corundum grown via the Czochralski (melt) process. In the 1970s, immense lab-grown sapphires were used for a variety of applications. Manufacturers cut this melt material into large, thick rectangular slices to make windows for helicopter gunships. The physical properties of sapphire could blunt the tips of incoming rounds, preventing penetration into the aircraft. Photo © Joel E. Arem, PhD, FGA. Used with permission.

How are Lab-Grown Sapphires Made?

Whether under the Earth or in a laboratory, crystal gemstones develop or “grow” when the right combinations of minerals interact under specific chemical and physical conditions. Of course, the chief advantages of synthesizing gems in a laboratory (from the manufacturer’s perspective) are time and financial savings. In a lab, manufacturers can control and even accelerate chemical and physical processes as well as combine minerals that occur rarely in nature. In effect, labs can create to order gems difficult or expensive to mine.

Synthetic star rubies and sapphires

All gem varieties of corundum can be synthesized through various methods, including the coveted “star stone” sapphires and rubies, such as these “Heller Hope” star gems. Photo © Joel E. Arem, PhD, FGA. Used with permission.

There are two types of methods for artificially creating sapphires: melt processes, which involve melting aluminum oxide into a sapphire droplet, and solution processes, which grow sapphire crystals in a solution.

Melt Processes

The most inexpensive and oldest melt process is known as flame fusion. In this method, a flame melts aluminum oxide powder (the principal mineral in corundum). The drops form into a long teardrop shape called a “boule.” The addition of other minerals to the aluminum oxide can create colored varieties of sapphire. Also, adding chromium to the aluminum oxide will create synthetic ruby.

The Verneuil process is a flame fusion process that can create sapphires much larger than those commonly found in nature.

lab-grown sapphires and rubies

Flame fusion creates long, tear-shaped pieces of synthetic corundum. This sample, consisting of a mix of aluminum oxide and chromium, would have yielded a synthetic ruby. This piece, on display at the Natural History Museum in London, UK, was removed from the flame fusion process before completion. Photo by Aramgutang. Public Domain.

Another melt process, the Czochralski process, uses radio waves to melt the aluminum oxide. A rod tipped with a seed crystal is inserted into the mixture and slowly rotated and pulled out, creating a column of sapphire. Although an expensive way to synthesize sapphires, it can create up to 4” of crystal per hour.

Solution Processes

Hydrothermal synthesis is a solution process that closely mimics natural formation, subjecting the minerals to intense heat and pressure in a sort of “pressure cooker.” Sapphires form around a seed crystal as the mineral solution rises to the top of the cooker.

Chatham lab-grown sapphires

Chatham sapphires, like these, are created via a flux solution method. Hexagonal crystal approximately 3 inches across. Photo © Joel E. Arem, PhD, FGA. Used with permission.

Are Lab-Grown Sapphires Really Sapphires?

Chemically and physically speaking, the same materials constitute natural and lab-grown sapphires, and they have the same atomic structure and crystal habit. Gemology labs would identify both lab-grown and natural sapphires as forms of corundum.

As a consumer, however, you may want to make a distinction between lab grown and natural. Both can be beautiful, but it is best to know exactly what you are paying for. If you encounter a sapphire offered for sale as synthetic, you can make an informed choice to buy or not. On the other hand, if offered for sale as a natural, you  must realize the possibility exists for misrepresentation or error in its identification.

For a very thorough and informative discussion of important caveats when gemstone buying, read our series on understanding gem synthetics, treatments, and imitations.

How Can Gemologists Distinguish Lab-Grown Sapphires From Natural Sapphires?

Distinguishing lab-grown sapphires from natural sapphires is challenging, but each artificial creation method leaves telltale signs that an expert gemologist can identify.

Melt processes like flame fusion may create sapphires that exhibit curved growth lines and curved color bands not found in nature. The Czochralski process also may produce gems with inclusions like gas bubbles and smoky veils. Hydrothermal synthesis may leave distinctive “nail head” inclusions.

artificial sapphire - lab-grown sapphires

Artificial sapphire, photo by maicos. Licensed under CC By 2.0.