Gemstones have been treated to change their appearance. While purchasing a gem it might come to your mind whether the gemstone is treated or not. These treatments are not always detected by the unpracticed eyes and sometimes also difficult to distinguish even by experts. There is a short description of some treatment processes: –
Bleaching is the process done to reduce or change the color of a porous gem. Only some gems can be bleached to remove the unwanted color from the gemstone. Bleaching is done by using acids, hydrogen peroxide, or similar oxidizing agents. The most commonly seen bleached gems are jadeite, pearls, and corals.
There is a breakdown in the structure of gemstones due to acid bleaching. So, most bleaching is going after impregnation to enhance durability and strengthen the color. It is almost impossible to detect one-step bleaching but after impregnation, it becomes easier to detect by magnification and analytical techniques used by a qualified gemological laboratory. Bleached gemstones are more brittle and more porous thus becoming more absorbent towards oils and liquids.
It is a technique used to alter a gemstone’s appearance by applying a coloring agent like to paint to the back surfaces of gemstones, which is called backing. The modern coating methods use metal oxide thin films. Diamonds, pearls, tanzanite, topaz, coral, and quartz are the most commonly encountered gems.
This treatment is easy to detect by a skilled gemologist besides the coating substance is colorless. These thin films are softer and do not adhere well to the underlying gem, so they are easy to scratch especially at the edges and junctions. It is necessary to avoid your coated gem from striking any hard objects and should be stored in a dry and soft container.
Dyeing is one of the oldest gemstone treatments. The first requirement for the coloration is that the gem should be porous or fractured. These fractures(also called pores) are sometimes purposely induced by heating the gem to impart the desired color. These pores are extremely minute but can easily be detected by a qualified gemologist.
The durability of dyed porous material may be long-lasting but eventually depends on the stability of the dye. Many dyes can fade with exposure to the ultraviolet rays of sunlight and some dyes can be removed when comes in contact with a solvent such as alcohol or acetone.
Dye is used for enhancing the appearance of lower-quality natural pearls and this treatment has been used since ancient times for gems such as coral, ruby, quartz, emerald, nephrite jade, turquoise.
To alter the color and to increase clarity, the gem is heated at high temperatures. Heating is either used to lighten, darken, or alter the color of a gemstone. The temperature required to alter color varies from 400 degrees Fahrenheit to 1300 degrees Fahrenheit.
A computer-controlled burnout furnace is the best tool for heating the treatment of gems. It allows steady changes in temperature due to which the thermal shocks are reduced that are responsible for destroying many gems. Intense heat may extend gems slightly more brittle than usual so care must be taken while heating.
Amber, amethyst, aquamarine, citrine, ruby, sapphire, tanzanite, topaz, tourmaline, zircon are the gemstones that undergo a heat treatment process to alter their color. All these treated gemstones are considered durable and permanent under normal handling conditions.
In this treatment, the gem is exposed to an artificial source of radiation to change its color. Sometimes this treatment is followed by heat treatment which is also called combination treatment. The most commonly encountered irradiated gems are diamond, corundum, topaz, pearl, quartz, etc.
Some irradiated gems fade when exposed to strong light. For example, blue topaz, diamond, and quartz have very stable colors but are damaged when exposed to high temperatures.
It is the process that uses heat and chemicals to diffuse an element into the atomic lattice of a gemstone to artificially change its color. ruby, sapphire, and feldspar are some gems that are diffused to change or accentuate their color. This treatment is considered to be permanent and it is extremely difficult to detect.
These are some gemstone treatment processes that are being used for the alteration of color. Cavity filling, impregnation, laser drilling, lattice diffusion, and high-pressure, high-temperature treatment are some other methods that are used for the alteration as well as increase the clarity of the gemstones.