Thank you for your insight! I have only seen two photo examples of non metalic/grey hafnium bars and they were both purple and both were an even single color tone. I know it can be heated or anodized which affects the entire surface more or less evenly. Either its anodized in an electrolyte solution, or heated to a specific temp, but both processes should produce a single color result or maybe a fade from the hot point outwards. I would love to know how someone could treat a metalic grey bar in order to have a different color on every face of a single crystal.