International Gemstone Market in Chanthaburi, Thailand: Shopping for Colored Stones by GemSelect. Gemstone & Mineral Glossary - Gemstone Information - GemSelect. Precious and Semi-Precious Gemstone Glossary Gemstone Hardness - How durable is your gemstone?. Gemstone Care - Gemstone Information - GemSelect. Zircon - to produce red, blue, or colorless stones.īirthstones by Month, Zodiac and Anniversary Stones. This is usually done with the green and blue varieties.
Tourmaline - to lighten darker shades of tourmaline. Topaz - when used with irradiation, heat treatment will produce shades of blue. Tanzanite - to produce a more desirable blue shade. Sapphire - to lighten or intensify color and to improve the uniformity of the color. Ruby - heat treatment improves color, removes iron stains, dissolves inclusions and fills tiny cracks. Morganite - heat treatment changes the color from orange to pinkish. Also deepens the color.Ĭitrine - often produced by heating varieties of quartz. Īmethyst - lightens the color and will change the color of pale amethyst to "yellow" that will be sold as citrine.Īquamarine - removes the greenish undertones that are common in this stone to produce a more blue stone.
YELLOW AMETHYST VS HEAT TREATED AMETHYST FULL
Here is a full list of the more commonly heated stones and how heat treatment enhances them. This allows us all to have the chance to own a colored gemstone that we can be proud to show.Īmethyst, citrine, ametrine, aquamarine, tourmaline, topaz, light green tourmaline, sapphire, ruby, tanzanite, and blue zircon are gemstones that are typically color-enhanced by heat treatment. The old, crude methods are gone, but the result is still the same drab gemstone are turned into something beautiful. Today, the technology is much more sophisticated, with professionals using large computer controlled electric furnaces. They would use pieces of bamboo to blow air into glowing charcoal where a few stones were placed, in an attempt to coax some new colors into their stones. An absence of such evidence could suggest an untreated stone.Ĭenturies ago, men sitting in front of charcoal fires were the first practitioners of the art of heat treatment. A gemologist can easily see this using a microscope. For example, if the stone has been treated, tiny inclusions such as small crystals will melt during the heat treatment process. For example, gemologists can examine the inner workings of the stone and study the inclusions for signs of heat treatment. However, there are some clues that can help. Unadulterated stones can be harder to verify. It is usually more difficult to find out if a stone has not been treated than if it has. These are caused by borax-based substances that are used in the heat treatment process. On rubies, inclusions may be found that are glassy in appearance.
For gems that contain rutile needles, the needle margins may become diffuse. The destruction of gas or fluid inclusions or the dissolving of mineral inclusions are clues to heat treatment.
These milky white sapphires turn blue, and account for many of the quality sapphires on today's market.ĭetection of heat and diffusion treatment is possible because these treatments modify natural inclusions. The same can apply to a type of sapphire known as gouda sapphire. This allows the chromium in the stone to combine with different atoms, allowing for a better red hue. Ruby is heated almost to its melting point, allowing the aluminum oxide in the stone to reform, creating a new crystal structure. Only the most valuable and expensive rubies possessing the richest colors are not heat-treated. This is a stone that is commonly heat treated. This heat treatment is permanent and irreversible.Īnother example is ruby.
An example of this is the dissolving of rutile silk inclusions in blue sapphires, which improves both clarity and color. This color change may result in the stone being darker, lighter, more intense or of a different color. During treatment, the stone is heated to very high temperatures (approximately 1600 Celsius) causing inclusions, chemical elements, and other impurities to reform themselves and change the color of the stone. Heat treatment is considered to be a natural type of enhancement as it is a continuation of the processes that occur in the earth when the stone was originally formed.
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