Abstract: A method the electron-beam irradiation of gemstones for uniform color enhancement requiring an electron-beam source having a capacity of 500 kW generating energy of between 3 MeV to 50 MeV. The method requires the gemstones to be moved in and out of the electron-beam path with the electron-beam source also being oscillated but in a direction ninety degrees opposed to the gemstones. Cooling means for the gemstones are also required to prevent heat stress cracking. Gemstones such as beryl, diamonds, quartz, sapphires, tourmaline, dark pearls and other minerals are suitable. More particularly the method relates to the treatment of topaz.