– exposure of a gem to an artificial source of radiation to change its color. This is sometimes followed by a heat treatment to further modify the color. This second step also known as a “combination treatment.
1. The most commonly encountered irradiated gems include:
Diamond – Neutron and electron radiation are the most common forms of artificial irradiation, and it is possible to induce black, green, blue green, deep yellow, orange, pink and red diamonds (often combined with a secondary step of heating, to achieve certain colors).
Colorless and other diamonds (left) can be artificially irradiated causing a variety of colors. Some of the irradiated colors are then heated as a second step, resulting in additional colors (group right).
Corundum – Some bright orange colors are induced in sapphires with a pale yellow natural color. The color in these is not stable and fades upon exposure to light.
Topaz – colorless topaz has little commercial value in the gem market today, but it can be subjected to artificial radiation to dramatically change its color. Used in conjunction with heat treatment, a variety of strong blue colors can be achieved for topaz. Pearl – Some pearls are irradiated resulting in dark gray colors.
Quartz – Varieties of quartz may be irradiated to produce amethyst, and some combination treatments that include heating after irradiation resulted in green quartz.
Other gems – Some varieties of beryl and spodumene can be irradiated to deepen an inherent color, or change the color altogether.
2. Durability factors – some irradiated gems’ color fades upon exposure to strong light. Blue topaz, diamond and quartz tend to have very stable colors as long as they are not exposed to high temperatures (this is especially true for irradiated colored diamonds, whose colors may be damaged if the diamond is exposed to the heat of a jeweler’s torch during jewelry repair procedures).
3. Detectability – Because strong blue colors do not occur naturally in topaz, such stones are considered to have undergone irradiation treatment. Strong colors in green, pink, and red diamonds should also be considered suspect. Determination whether a colored diamond is natural color or treated color requires examination by an experienced gem-testing laboratory.
4. Encountered in the trade – Extremely frequent for topaz, and frequent in fancy color diamonds.
5. Special care requirements – In the beryl and spodumene gemstones, the irradiated color tends to be short lived and fades upon exposure to bright light. Otherwise, there are no special care requirements for most irradiated gem materials.
Source: Robert Weldon, www.gia.edu
To learn more about gem treatments see also: