Depending on the original stone color, the Van de Graff generator method is capable of producing bluish hues. The common cape (yellow) diamonds used in this process, change to a bluish-green or greenish-blue. These treated diamonds are very common, so be aware of the likelihood of irradiation. To get the result of a straight blue diamond, a colorless stone must be used, and even then there are no guarantees. Obviously using the scarcer colorless category for irradiation purposes is not appropriate. To detect this color treatment, a lab checks a blue diamond for electrical conductivity. A natural blue diamond usually contains traces of boron, which causes it to conduct small electrical currents. On the other hand, a treated blue diamond incurs a structural change in its lattice, which renders it non conductive. Very rarely do non-conductive, bluish-gray or greenish-blue, natural color diamonds appear in the market