So, can you tell the difference between natural sapphires and lab-grown sapphires? [Reading time: 4 min]
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.
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.
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.
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.
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.
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.