Gemstone Treatments

The treatment of gemstones to increase their beauty and value is an integral part of the modern gemstone industry, and in fact, has been practiced for hundreds of years. For example, as far back as the 11th-century, emeralds have been treated with oils to help mask some natural fissures that may have reached the surface of the stones. That practice is still being done today, although with more modern oils and with pressure to penetrate deeper into any surface reaching fissures in the stones. Furthermore, recent advances in gemstone treatments have significantly increased the availability of many formerly “rare” gemstones, and made it possible for the average consumer to possess gemstone jewelry that was once reserved only for the very wealthy. However, while these treatments are commonplace and well known within the industry, the general public’s awareness has been much lower.

To help our customers better understand gemstone treatment in general, we would like to provide the following information on specific treatments to many popular gemstones:

Amethyst - this stone may be heated to lighten very dark purple crystals prior to cutting. The treatment is permanent, although only occasionally used.

Aquamarine - this stone may be heated to remove yellow components and produce a purer blue color. Typically, aquamarines are a pale greenish blue when mined, and most stones are heated to provide the more popular light blue color. Interestingly enough, in the past the natural greenish blue stones were more popular, but the pure blue has become more in vogue in recent years. The treatment is permanent and is a common practice in the industry.

Citrine - this stone is also heated to improve the color. Actually, many citrines are really just amethysts that have been heated to higher temperatures, where the purple fades completely and the yellow color dominates. In Brazil, these stones are known as “ametista queimada” or “burnt amethyst”. The color change is permanent (although the purple color could be restored through irradiation).

Diamond - too many treatments are available to adequately describe here. However, diamonds have been treated with clear resins or glasses to mask surface reaching fissures, they have been “drilled with lasers” to burn out carbon inclusions, they have been treated with radiation to provide unique colors, and they have been treated with high temperatures and pressures to “whiten” off-white stones. Most of these treatments are permanent, except for the resin treatment.

Emeralds - as indicated above, the vast majority of emeralds is typically treated with oils or epoxy polymers to help mask surface reaching fissures. Furthermore, emeralds should never be subjected to ultrasonic cleaning since that process may remove the oils or polymers.

Opal - in the past, some of these stones have been treated with sugars and sulfuric acid to darken the background color and make the stones livelier. There are also opal doublets (slice of opal on a dark background such as onyx) and opal triplets (essentially an opal doublet with a quartz cap on top). The opal doublets and triplets are stable, but should not be allowed to get wet since water could enter between the layers. The quartz cap on the opal triplet significantly improves the durability of the stone.

Pearls - can be bleached, dyed, or chemically enhanced to improve color and appearance. These treatments are usually permanent, although some dyed pearls may fade in direct sunlight.

Ruby - these stones are usually heated to very high temperatures to help improve the clarity, color, and appearance. The treatment is permanent.

Sapphires - these stones are also usually heated to help improve the clarity, color, and appearance. They can also be treated by diffusion, where certain metal ions are diffused into the surface under very high heat. Depending on the metal ions used, the diffusion process can improve the blue color, as well as form a pinkish orange color that is very rare in nature. This process is permanent, but may only color the outer layer of the stone (depending on diffusion temperature and time), hence any deep scratch may remove the color.

Tanzanite - this stone is very rare in nature, but has become more “plentiful” through treatment of Zoisite (actually, tanzanite is just a special name for blue zoisite). However, almost all zoisite is found as unappealing greenish brown crystals, but heating these stones to relatively high temperatures (around 600 degrees Celsius) transforms the zoisite into the popular, vibrant violet-blue Tanzanite. In essence, if you didn’t heat treat zoisite, you would never have tanzanite.

Topaz - blue topaz is commonly produced by irradiating and then heating “white” topaz. The treatment is permanent. Virtually all blue topaz on the market today owes its color to this irradiation and heat treatment process. Recently, several companies have also launched “surface coated” topaz in a wide variety of iridescent colors (reds, greenish blues, greens, oranges, etc.), but since these treatments are only on the surface of the stone, they may be subject to scratching.

Tourmaline - some very dark green and dark blue green tourmalines are heated to lighten their colors. The treatment is permanent and only occasionally performed. Many gem dealers believe that this process just “finishes up what Mother Nature intended” and it is virtually impossible to distinguish heated from unheated tourmalines.