Gemstones Treatments

Heat can improve gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in “ametrine” – a stone partly amethyst and partly citrine. Aquamarine is often heated to remove yellow tones, or to change green colors into the more desirable blue, or enhance its existing blue color to a purer blue.

Nearly all tanzanite is heated at low temperatures to remove brown undertones and give a more desirable blue / purple color. A considerable portion of all sapphire and ruby is treated with a variety of heat treatments to improve both color and clarity.

When jewelry containing diamonds is heated (for repairs) the diamond should be protected with boric acid; otherwise the diamond (which is pure carbon) could be burned on the surface or even burned completely up. When jewelry containing sapphires or rubies is heated, those stones should not be coated with boracic acid (which can etch the surface) or any other substance. They do not have to be protected from burning, like a diamond (although the stones do need to be protected from heat stress fracture by immersing the part of the jewelry with stones in water when metal parts are heated).

Here, we provide an overview of the most common gemstone treatments:

Heat Treatment

Heat treatment is one of the oldest and most widely used methods for enhancing the color and clarity of gemstones. Gemstones are heated to high temperatures under controlled conditions to alter their internal structure and enhance their color. This process can lighten, darken, or change the hue of a gemstone, as well as remove or reduce visible inclusions to improve clarity. Heat treatment is commonly applied to a variety of gemstones, including sapphires, rubies, and topaz.

Dyeing refers to one of the oldest treatments recorded. The treatment involves the introduction of a coloring agent into a gemstone to give it a new color, intensify an existing color or improve color uniformity.

Irradiation involves exposing gemstones to various forms of radiation, such as gamma rays or electron beams, to alter their color. This treatment can produce vibrant colors in gemstones that are naturally pale or undesirable in hue. Irradiated gemstones may also undergo subsequent heat treatment to stabilize their color. Commonly irradiated gemstones include diamonds, topaz, and certain varieties of quartz.

Virtually all blue topaz, both the lighter and the darker blue shades such as "London" blue, has been irradiated to change the color from white to blue. Most greened quartz (Oro Verde) is also irradiated to achieve the yellow-green color. Diamonds are irradiated to produce fancy-color diamonds (which occur naturally, though rarely in gem quality).

Oil treatment is commonly used to improve the clarity and appearance of certain gemstones, particularly emeralds. Gemstones with visible fractures or surface-reaching inclusions may be treated with colorless oils or resins to fill these voids and improve their overall appearance. While oil treatment can enhance the beauty of gemstones, it may also be temporary and require periodic reapplication. Emeralds containing natural fissures are sometimes filled with wax or oil to disguise them. This wax or oil is also colored to make the emerald appear of better color as well as clarity. Turquoise is also commonly treated in a similar manner.

Fracture filling has been in use with different gemstones such as diamonds, emeralds and sapphires. In 2006 "glass filled rubies" received publicity. Rubies over 10 carats (2 g) with large fractures were filled with lead glass, thus dramatically improving the appearance (of larger rubies in particular). Such treatments are fairly easy to detect.

Coating

Surface coating, also known as "enhancement" or "coating," involves applying a thin layer of colored or reflective material to the surface of a gemstone to improve its appearance. This treatment is often used to enhance the color or luster of gemstones, such as pearls and certain types of topaz. However, surface coatings can be fragile and may wear off over time or when exposed to certain chemicals or conditions.

Diffusion

Diffusion involves introducing chemical elements, such as beryllium or titanium, into the surface layers of a gemstone to alter its color. This process can create vibrant and unusual colors in gemstones that would otherwise be less desirable or valuable. Diffusion-treated gemstones may require careful examination to detect the presence of treated areas, as the treatment can sometimes be difficult to detect.

Bleaching

Bleaching is a treatment method used to lighten or remove unwanted coloration from certain gemstones. Bleaching agents are applied to the surface of the gemstone to break down pigments and remove or reduce the appearance of undesirable colors. This treatment is commonly applied to pearls and some types of coral to improve their marketability.

Disclosure of Treatments

It's important to note that disclosure of gemstone treatments is a critical ethical consideration in the gemstone industry. Gemstone dealers and retailers are typically expected to provide accurate information about any treatments that have been applied to gemstones to ensure transparency and consumer confidence. Additionally, gemstone buyers should educate themselves about common treatments and ask questions about the treatment history of gemstones before making a purchase. This allows consumers to make informed decisions and select gemstones that align with their preferences and values.

Detection of Treatments

Detecting treatments can be challenging and often requires specialized equipment. However, some general signs might indicate a treatment, such as unusual color uniformity, presence of fractures filled with a different substance, or an overly glassy luster.