Which is the best to buy: natural, enhanced, imitation, artificial or synthetic gems? The answer depends on how you plan to use it.
Natural gemstones have not had anything done to them that changes their color, stability or durability. They may only be polished or cut to show off their beauty. Natural stones often have imperfections in them, and can be quite expensive.
Many gemstones are enhanced, which may improve or change the color, provide stability or increase durability. Stability means that the stone won’t change color under normal conditions. Durable stones won’t scratch or break when worn. The four main methods of enhancement are heat treatment, irradiation, chemical treatment and assembly. While some enhancements are done with an intent to deceive, many gemstones would not be usable in jewelry if they weren’t treated in some way.
The results of heat treatment and irradiation often mimic what Mother Nature would have achieved had the stones been left in the ground a few more centuries. Chemical enhancements are generally used to change the surface characteristics of gemstones and assembly is often used to protect fragile stones.
Heat treatment is commonly used to improve color. Color changes resulting from heating are permanent in most gemstones. Amethyst, ruby, sapphire, topaz, tourmaline and zircon all are routinely heat-treated. Most aquamarine now sold has been heated to change it from its natural green to the blue that is currently popular.
Irradiation is also used to change or deepen gemstone colors. Clear topaz is irradiated to produce blue topaz, and colorless tourmaline may be changed to any one of several colors. Some diamonds are irradiated to improve their color. Irradiation is not always permanent; some irradiated stones revert to their natural colors when exposed to extreme heat or light.
Heat treatment and irradiation are generally undetectable.
Chemical treatment of gemstones includes bleaching, dyeing and staining. It also includes the uses of oils, waxes, resins or plastics to stabilize or change the appearance of a gemstone. Chemical treatments are often called impregnation, because the chemicals usually penetrate the surface of the stone. Porous stones,
like turquoise, are frequently sealed with wax or resin to keep the color from fading. Oils, waxes and plastics are used on many stones to hide small scratches and surface flaws. Coral, ivory and pearls may be bleached. Nearly all gemstones can be dyed or stained. Some chemical treatments are permanent. Others will dissolve in solvents like acetone or in ultrasound cleaners. Waxes melt when exposed to heat or strong light. Bleaching can be impossible to detect. Dyeing can usually be detected with a microscope.
Assembled stones may be composites like doublets and triplets, or they may be foilbacks. A composite stone is two or three pieces of material fused or joined by colorless cement. Although any stone may be made into a composite, opals are the best-known. An opal triplet consists of a piece of good opal sandwiched between a top layer of clear quartz and a bottom layer of low-quality opal. A doublet is usually good opal underneath a quartz layer. The quartz helps protect the delicate opal. Composites also allow the use of gemstones too small to be used otherwise.
False composites contain no gemstone material. False opal doublets are made from crystal cemented over abalone shell.
Foilbacks have been made for nearly 4,000 years, using a variety of techniques. One kind of foilback involves placing a backing of foil or a metallic coating on a stone to give it a more brilliant color. Cat’s-eyes and star effects are created with etched backings. Rhinestones are one example of a popular foilback.
Imitation, or simulated, gemstones may be natural (substitutes) or manmade (artificial). Substitutes are cheaper look-alike stones. Red spinel or garnets may be substituted for ruby, and green tourmaline is used to replace emerald. Cubic zirconia, a manmade stone from a natural substance, is a well-known substitute for diamond.
Glass is a time-honored way of making gems. Glass imitations have been found in Egyptian tombs that are at least 5,000 years old. Non-transparent glass was first used to make artificial turquoise, lapis lazuli and onyx. Artificial gemstones of all varieties were later made from paste, which is a very hard kind of transparent glass. Glass is often used now to make artificial jade and opal. Plastic is also frequently used for artifical gems, particularly the organic ones like amber, ivory and coral.
A synthetic gemstone is laboratory-grown, or manufactured. All the chemical, physical and optical characteristics of synthetic gemstones are identical to their natural counterparts. Good synthetics have been made since the early 1900’s. Because they mimic natural stones so well, most synthetics are difficult to detect, even by experts. Often, the only clue is the physical perfection of the stone–synthetics are usually flawless, while natural stones contain imperfections. Alexandrite, amethyst, coral, diamonds, emeralds, jade, lapis lazuli and opals are a few of the synthetic gemstones available. Reconstituted gems fit into a separate category. Although they do contain genuine material, experts regard them as imitation. Reconstituting, or reconstructing, means that small fragments of gem material have been combined to form a large piece. Amber and turquoise are two common examples.
Reconstituted amber, typically called ambroid or pressed amber, is made from scraps and shavings generated by amber carvers. The tiny pieces are collected and heated, then pressed into large blocks. Manufacturers of ambroid can easily insert insects to make it look even more like natural amber.
Reconstituted turquoise is made from inferior grades of turquoise that have been powdered. The powder is mixed with an adhesive and dye mixture to form a solid mass, which is then cut into shapes.
Although there is a special pleasure in working with natural gemstones, they aren’t always the best choice. Purchase your gems from a reputable dealer, then select what will best fit your needs.