Could you tell the difference between natural sapphires and lab grown sapphires?
Sapphires have been highly prized for ages. Their beauty and hardness make them ideal choices for jewelry. The demand for sapphires, however, has long exceeded the natural supply. (Gem quality corundum, which includes sapphires and rubies, is more rare than diamonds). Not surprisingly, sapphires and rubies were some of the first gemstones to be synthesized. The first lab grown sapphires were made over 100 years ago. Some of the technological methods used then are still used to synthesize sapphires today.
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. Chemical and physical processes can be controlled and accelerated in a lab, and combinations of minerals that occur rarely in nature or are difficult to mine can also be created to order.
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, aluminum oxide powder (the principal mineral in corundum) is melted with flame. The drops form into a long teardrop shape called a “boule.” Other minerals can also be added to the aluminum oxide to create colored varieties of sapphire. (Adding chromium 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. This is an expensive way to synthesize sapphires but it can create up to 4” of crystal per hour.
Hydrothermal synthesis is a solution process that closely mimics natural formation. The minerals are subject 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, lab grown sapphires are made from the same materials as natural sapphires and have the same atomic structure and crystal habit. Both lab grown and natural stones would be identified 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 a sapphire is offered for sale as synthetic, you can make an informed choice to buy or not. If a sapphire is offered for sale as natural … you must be aware of the possibility of misrepresentation.
For a very thorough and informative discussion of important caveats when gemstone buying, see “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 may create sapphires that exhibit curved growth lines and 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.
If you have a sapphire, or any gemstone, you’d like to have evaluated professionally and securely, the International Gem Society offers a gemstone identification and appraisal service.