Treatments, Synthetics, Simulants:
What to Know Before Buying a Diamond
There is no gemstone in the world quite like a diamond. Formed by nature, the average diamond is 3.3 billion years old. Rare and valuable, a diamond is a testament of endurance and strength, with unsurpassed brilliance and fire—a natural symbol of everlasting love.

It’s not surprising then, that techniques and lookalikes have been developed to enhance and replicate a diamond’s beauty. In recent years, treatments to improve a diamond’s clarity and color, synthetic diamonds and simulated diamonds have become more common, more advanced and harder to detect.

The Gemological Institute of America (GIA)—the world’s foremost authority on diamonds and the creator of the Four Cs and the International Diamond Grading System—is a nonprofit organization that feels consumers have a right to know if a diamond is natural, laboratory-created, a simulant, or has been treated to enhance its appearance, especially since it affects the stone’s value.

GIA researchers have thus made numerous breakthrough contributions to our understanding of these techniques. Here the organization provides the following information about treated, synthetic and simulated diamonds as well as its reporting procedures for these stones, to give consumers the ultimate assurance in the diamond they’re purchasing.


Clarity Enhancements
Natural diamonds are the result of carbon that’s been exposed to tremendous heat and pressure deep in the earth. This process can result in a diamond having a variety of internal characteristics called “inclusions” and external characteristics called “blemishes” that adversely affect its clarity.

One technique for improving a diamond’s clarity is called laser drilling, which is commonly used to remove small dark inclusions in a diamond. A laser bores a small hole into the diamond’s interior and burns away the inclusion, thus vaporizing the material with the laser’s extreme heat, or creates a channel through which a bleaching agent can be introduced to improve the inclusion’s appearance. The GIA, which can identify any known diamond treatment, will issue grading reports for diamonds that have been drilled, disclosing the treatment on its report.

Fracture filling, meanwhile, hides white fractures in a diamond called “feathers.” A glass-like substance is injected into the fracture to make it less visible and to improve the stone’s clarity by one or two grades, however, because it’s not permanent—the filling might be damaged or removed during routine jewelry cleaning and repair— therefore the GIA will not issue grading reports for diamonds that have been fracture-filled.

Color Enhancements
The color of most gem-quality diamonds is evaluated based on the absence of color, with a chemically pure and structurally perfect diamond having no hue and thus a higher value. Truly colorless diamonds are very rare; most diamonds used in jewelry are nearly colorless with tints of yellow or brown.

One technique for improving a diamond’s color is called HPHT (High-Pressure, High-Temperature), which is an effective laboratory process for permanently changing the color of Type IIa diamonds to make them colorless, or to give other diamonds a variety of attractive colors such as pink, blue, green, yellowish green or yellow. Type IIa diamonds have no trace amounts of nitrogen and thus are extremely transparent. They are much rarer than the vast majority of diamonds mined, known as Type I diamonds, which have trace amounts of nitrogen in their atomic structure that causes the yellowish color. The GIA will issue grading reports for diamonds that have been HPHT-processed, disclosing the treatment on its report. As an added precaution, the GIA also laser-inscribes the girdles of diamonds it identifies to be HPHT-processed.

Coating, meanwhile, enhances a diamond’s color by masking an undesirable body color with an ultra-thin layer of chemicals or plastics. Another form of coating involves applying a thin film of synthetic diamond to the surface of a diamond simulant, giving it certain characteristics of a real diamond. Since this treatment, like fracture filling, is considered nonpermanent or unstable, the GIA will not issue grading reports for diamonds that have been coated.

Synthetic diamonds, also known as laboratory-created diamonds, laboratory-grown diamonds and (manufacturer name)-created diamonds, are produced by a man-made technological process, as opposed to natural diamonds, which are created by a geological process. In the last 30 years, gem-quality synthetic diamonds have been grown in Japan, Russia, South Africa, the Ukraine and the United States.

Synthetic diamonds have essentially the same chemical composition, crystal structure and optical and physical properties of diamonds found in nature, and most are categorized as either HPHT (High-Pressure, High-Temperature) diamonds or CVD (Chemical Vapor Deposition) diamonds, depending on their method of production.

The HPHT process for producing synthetic diamonds uses equipment that replicates the intense heat and pressure that create natural diamonds deep inside the earth. HPHT synthetic diamonds have been produced in a variety of colors, including yellow, blue, green, pink, red and purple, as well as colorless. Physically, optically and chemically they are nearly identical to natural diamonds, but a trained gemologist using standard gem-testing equipment, such as a gemological microscope, a polariscope, a spectrometer and a refractometer, can identify them.

Synthetic diamonds produced using the CVD method are grown at low pressures and relatively low temperatures. This growth technique can produce thin, brown to near-colorless, synthetic diamond crystals that are suitable for faceting for jewelry purposes. Synthetic diamonds grown by this method are considered “purer” than those grown by the traditional HPHT technique and are therefore more difficult to detect.

While synthetic diamonds represent a small segment of the market, they are becoming more widespread and increasingly difficult to detect, the GIA says. The organization tests every diamond to determine if it is natural. If a diamond is found to be laboratory-grown, the GIA issues a Synthetic Diamond Grading Report. As an added precaution, the GIA also laser-inscribes the diamond’s girdle with a report number and a statement that the diamond has been laboratory-grown.

Diamond simulants have a similar appearance to natural diamonds, but unlike synthetic diamonds, they differ from diamond physically and chemically.

A colorless cubic zirconia totaling 1.77 carats. Image © GIA.

The two most common examples are glass and cubic zirconia, also referred to as CZ. Cubic zirconia is a synthetic, cubic crystalline form of the metallic element zirconium dioxide. It’s almost as brilliant as diamond, has great fire and is relatively hard, giving it good durability and wear. But both cubic zirconia and glass are completely unrelated to diamond at the atomic level and have optical and physical characteristics that can be identified by a trained gemologist.

Synthetic moissanite is fairly easy to identify with a microscope or a loupe. When you look through the crown, doubling of the back facets readily reveals the doubly refractive nature of this diamond simulant. Magnified 20×. Image © GIA.

Another diamond lookalike being sold today is called moissanite (named after Dr. Henri Moissan, the French scientist who discovered it), which is chemically known as silicon carbide, a compound mineral composed of silicon and carbide that occurs so rarely in nature and in such extremely small amounts that it’s not available for jewelry use. Therefore, silicon carbide is now being manufactured in gem-quality sizes in laboratories and then faceted by gem cutters to bring out its natural brilliance. According to the GIA, synthetic moissanite is also a diamond simulant, with distinctive characteristics much different from those of a diamond. A trained gemologist can distinguish between the two.
The GIA tests every stone to verify that it is, in fact, diamond, and does not issue grading reports for diamond simulants.
Picchiotti Italy
Palmiero Italy
Carlo Barberis
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