Iron is not enough for sapphires, it must be combined with titanium. I do not know how this is done, but while the doping with chromium for rubies is simple, c

Iron is not enough for sapphires, it must be combined with titanium. I do not know how this is done, but while the doping with chromium for rubies is simple, chromium will just substitute aluminum in the crystal lattice and it will provide a color determined by its concentration, for sapphires there may be necessary a more complex thermal treatment, so that the iron and titanium will form the right type of coupled defects in the crystal, in order to have the desired color.