Knowing the ins and outs of gemstones doesn’t stop with knowing a ruby from a sapphire, or an amethyst from an aquamarine. If you’re looking for gemstone jewelry, you’ve probably been introduced to the idea that many different kinds of gemstones are treated to enhance their appearance prior to being sold. The reality is that only a very small percentage of well-known gemstones are considered “gem quality” without some form of treatment. One of the most common types is heat treatment, used to enhance already existing color, reduce inclusions, or produce a desirable color. So what does this mean for a jewelry buyer?
While the exact method of heat treatment can vary according to the type of gemstone being treated, in general the process subjects a gemstone to high heat over a period of time. In a sense, this is just an extension of the natural processes that produce gemstones in nature, because high heat is often involved in producing the exact hue of particular stones. Stones have been heat treated for centuries, and under normal conditions, the enhancements produced by heat treatment are considered permanent and durable. The effects of heat treatment may, in some cases, be evident to a trained gemologist closely examining a stone under magnification, but they will not be obvious to a casual observer.
Heat treatment is commonly used on a wide variety of gemstones. In fact, for many types of stones, it is safer to assume that they have been heat treated unless the seller and the gemological report for the piece you are considering tell you otherwise. Stones that are routinely heat treated include sapphire, ruby, tanzanite, tourmaline, amethyst, citrine, aquamarine, topaz, zircon, and morganite.
Whether or not such treatment is of concern to a buyer depends on that buyer’s personal preference and on how the stone is represented by the seller. A tanzanite that has been heat-treated to produce a more saturated violet-blue color is still a tanzanite, and still quite valuable, but less so than one that was never heat-treated. Some collectors prefer only untreated stones, willing to pay the premium prices such stones command and to accept that completely natural untreated stones may only be found in smaller sizes or with visible inclusions. Other buyers appreciate that heat treatment produces attractive gems at more affordable prices, putting them within reach of a wider audience.
As long as sellers disclose the true state of the gems they are selling, and buyers are fully informed about what they are getting, heat treatment and other forms of gemstone enhancement are an accepted part of the jewelry trade. This is why it is important to only work with scrupulous dealers, so that you can trust a stone they present as untreated is the real deal.
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