Gemstone value of the stone. Some treatments are used widely because the resulting gem is stable, while others are not accepted most commonly because the gem color is unstable and may revert to the original tone. Heat can improve gemstone color or clarity. The heating process has been well known to gem miners and cutters for centuries, and in many stone types heating is a common practice. Most citrine is made by heating amethyst, and partial heating with a strong gradient results in “ametrine” – a stone partly amethyst and partly citrine. Aquamarine is often heated to remove yellow tones, or
Gemstone irradiation coloring of the diamond's surface. Only high-energy radiation such as gamma ray or neutron can produce fully saturated body colors, and the sources of these types of radiation are rare in nature, which necessitates the artificial treatment in jewelry industry. Irradiation, particularly when done in a nuclear reactor, can make gemstones slightly radioactive, so they are typically set aside for a couple of months to allow any residual radioactivity to decay. The first documented artificially irradiated gemstone was created by English chemist Sir William Crookes in 1905, by burying a diamond in powdered radium bromide. After having been kept there