The reduction of the brown color component after LPHT annealing shows that high temperature heating, even performed without stabilizing pressure, is a way to improve color of brown CVD diamond. Brown
color of CVD diamonds has a different origin than that of natural brown diamonds, which is vacancy clusters. The brown color causing defects in CVD diamonds have lesser temperature stability and they
can be largely destroyed at relatively low temperatures, e.g. at 1600 “C [3]. In natural diamonds, the brown color component is much more stable and LPHT annealing alone, even when performed at a temperature of 2000 “C, is not effective in its removal (detailed account on LPHT treatment of natural brown diamonds will be published elsewhere).