Here are the different types of treatments commonly used in the jewelry industry today:
Cavity Filling – The surface-reaching cavities, pits, or other depressions in the surface of a gemstone can be filled with glass, plastic, or other substances. The shallow surface-reaching cavities in corundum, usually ruby, are usually filled with glass-like substances.
Coating – In order to add color or special effects to a gemstone, a thin layer of lacquer, enamel, ink, foil or film is coated on to the gem’s surface. The gems most often coated are turquoise, quartz, topaz or opal and now diamonds.
Diffusion - Chemical agents are used in the presence of heat to penetrate a shallow layer of the surface, become part of the crystal structure, and change the color or cause asterism. Sapphires and rubies can be diffusion-treated. Unlike coatings, the diffused substance is actually incorporated into the stone’s structure.
Dyeing – A gemstone’s color can be changed or improved by using chemicals. Pearls, jade and turquoise are commonly dyed.
Fracture Filling – Surface-reaching fractures, cleavages, laser drill holes and other voids can be filled with glass, plastic, or other substances to improve the gemstone’s clarity. The internal fractures of a diamond are filled with a transparent material that has the same refractive index as the diamond, thereby improving its clarity grade.
Heat Treatment – Gemstones are subjected to high temperatures in order to lighten, darken, deepen, or even completely change their color. In certain gemstones heat treatment is also used to improve clarity. For example, heat treatment may be used to develop or improve colors such as blue or yellow in sapphires; to remove colors, like yellow, from aquamarines, or blue from rubies; to improve transparency by dissolving silk in sapphires or removing gas bubbles in amber; or to induce asterism, as in corundum. Heating is generally permanent, and heated stones do not require special care.
Irradiation – This is used in gemstones like diamonds to affect only their color. Subatomic particles are used to bombard the electrons of the gem, causing them to be ‘knocked’ loose, and captured by other atoms. The light-absorbing pattern of the gems is thereby changed and as a result, so is their color. See Enhancement Process for details. This treatment is used to permanently create or intensify the gem’s color. Diamonds, topazes and aquamarines are often irradiated to enhance their color.
Laser Drilling – A laser is used to drill a hole in a diamond to reach a dark inclusion inside the stone. Chemicals are then inserted in order to bleach these black inclusions, thereby improving the appearance of the stone. The effects of the treatment are permanent and require no special care.
Oiling & Impregnation – This involves the filling of surface-reaching fractures with oil (in oiling) or a plastic polymer substance (in impregnation) to make them appear less noticeable. Emeralds are routinely oiled and jadeite is commonly polymer-impregnated.