Treatment of Topaz Gems

Topaz occurs naturally in a wide range of colors including shades of yellow, orange, brown, pink to Violet, and blue. With the exception of the pink to Violet shade which has color caused by the presence of chromium, all of the other colors are caused by imperfections in the topaz crystal called color centers.  Sherry yellow to brown tones that are commonly found in topaz crystals from both Utah and Mexico, are unstable and on continued exposure to sunlight will completely disappear, turning the stone colorless.

In the last 30 years or so, blue topaz, in a light shade similar to that of aquamarine, has become a very popular gem. In fact, it’s hard to imagine the jewelry industry without this gemstone staple, but few people know that virtually all these beautiful blue gemstones have been treated by irradiation. Some years ago, it was discovered that inexpensive, colorless topaz crystals could be treated by nuclear radiation and the ionizing energy of the radiation would change the color of the topaz. The radioactive energy slightly alters the crystal and creates a color center that gives color to the formerly colorless crystal. Upon irradiation, the topaz first turns a brown to brown green color.  The brown tone is temporary and hides the more desirable light blue coloration underneath. The brown tone can be removed with a gentle heating or even upon exposure to strong sun light for several days. Once the brown has been removed, an attractive and permanent blue coloration remains.  The types of radiation used to accomplish this change include gamma, beta (high energy electrons) and neutron radiation.

Not all of the colorless topaz takes on this blue coloration easily. Stones from Nigeria are reputed to have the highest percentage that take on coloration easily, with stones from Brazil also being used, but not as many will take on the blue color easily. The naturally brown stones from Mexico and Utah will not take on the blue coloration. For some stones gamma radiation is sufficient, for others a beta radiation is required, but nearly all colorless stones will turn medium to dark blue upon exposure to neutron radiation. The shade produced by neutron irradiation is deeper than the shades typically produced by Gamma or beta irradiation. This darker neutron induced shade is sometimes called “London” blue. The problem with neutron radiation is that it is more expensive than the other types of treatment and it also has the potential to make the stone radioactive as neutrons become absorbed by the impurities in the topaz.  Some stones even become radioactive enough that they present a potential safety hazard to the wearer.  These stones should not be worn. Radioactive topaz needs to be stored in a safe environment and sometimes it takes years for the radioactivity to decay enough so that the stone can be safely worn.

For More information on Topaz the gem, see my webpage at:
Topaz Gemstone Info page