Published: June 2012
Irradiation is a modern gemstone treatment, but it is also perhaps the oldest, naturally-occurring gem treatment. This is because there are natural sources of radiation in the earth. Many of these sources emit extremely low levels of radiation, but when a stone is exposed to these sources of radiation for millions of years, the cumulative effect can be great.
Irradiation is the bombardment of a material with various subatomic particles. This treatment can occur naturally, or it can be done artificially in a lab, a nuclear reactor or treatment facility. The effect is the similar, and, in many cases, there is no way of knowing if the original source of radiation was the earth or the laboratory. The artificial irradiation of gems is done to create or alter colors. Colors are created by adding or subtracting electrons within the crystal lattice, causing it to interact differently with the light, which we see as a change in perceived color. This can be a subtle to strong increase in color, or an entire change of hue. For radiation to have an effect on color, the atomic conditions must be right. Not all materials can be affected by radiation and most are not.
Today, most irradiated gems are treated in licensed facilities that also treat medical equipment for sterilization purposes and food to prolong shelf life. This type of facility will use a gamma-type radiation, usually cobalt-60, which leaves no residual radioactivity in the product. The final product is safe to handle immediately following treatment. The cobalt-60 is shielded and the materials are brought in on conveyor belts so employees are not exposed to any radiation. Stones commonly treated in this manner include most blue topaz, green quartz (prasiolite), golden beryl, pink tourmaline, kunzite and smoky quartz. Most of these materials may also be found naturally irradiated. Exact exposure times and number of exposures can vary by material and treater. Certain colors of blue topaz, such as London Blue, are treated by more than one type of irradiation in order to create that distinctive, deep blue hue.
After treatment, some gems are ready to sell, such as tourmaline and smoky quartz. Others, like blue topaz and diamonds, need an annealing process (usually heat) to stabilize the color. Some materials will not be stable, even with annealing. These materials are typically Maxixe beryl, certain types of topaz (rhyolitic) and kunzite. Some materials, after radiation, will revert at various rates to its original color or even become colorless if over-heated. Most irradiated gems sold are stable. Kunzite is one stone that is known to fade whether irradiated or not.
Some materials react better to different types of radiation. Diamonds and London Blue topaz are treated in cyclotrons or linear accelerators. These require annealing, as well as a cool-down period of weeks to months, until they stabilize and no longer emit radioactive particles.
While the actual process is based on complicated atomic science, years of research and study have proven which methods are safe, stable and reliable. The Nuclear Regulatory Commission (NRC) carefully regulates all irradiated products, and it requires a special license to import these materials. This is to ensure the gems have been properly treated in a reliable, trusted facility and to ensure the safety of those buying them.